Patrick Castel

Keywords: guidelines, organization, power, profession, standardization What's Behind a Guideline? Authority_, Competition

Taking the French oncology sector as a case study, this paper shows that guidelines are used strategically by individual physicians and groups of physicians. While some studies have made convincing arguments about the rise of guidelines as a manifestation of a new type of objectivity, this case study provides evidence that the proliferation of medical guidelines is also the result of an attempt by some physicians to improve their positions relative to competing groups. Guidelines could indeed be strategic resources used by professional actors at the expense of other professionals in order to (1) maintain a sufficient amount of activity and (2) increase control over therapeutic decisions. The study also points to other kinds of changes that guidelines may influence, beyond medical practices and coordination: the evolution of the structure of power relationships inside the medical profession. A perspective on the sociology of organizations, which places concrete exchange and bargaining relations at the core of its analysis and treats social control as being continually challenged and (re)produced, helps to identify other reasons why standardization does not prevent local specificities and may even enhance them.

This is consistent with well-known results on the inability of guidelines to reduce variations in organizational practice, and on the necessity of local negotiations and adaptation processes for sustaining everyday care practices and institutionalized patterns (Timmermans & Berg, 1997; Zuiderent-Jerak, 2007). Second, organizational studies conclude that the introduction of standards does not always benefit the actors who are in charge of their administration, such as supervisors and regulators [START_REF] Segrestin | La Normalisation de la Qualité et !'Evolution de la Relation de Production[END_REF][START_REF] Cochoy | Comment !'Ecrit Travaille !'Organisation: le Cas des Normes ISO 9000[END_REF][START_REF] Castel | Quand les Normes de Pratiques Deviennent une Ressource pour les Médecins[END_REF]. This conclusion is also echoed by recent empirical studies that question whether the development of medical standards contributes to the weakening of the profession's power and autonomy [START_REF] Berg | Guidelines, Professionals and the Production of Objectivity: Standardization and the Professionalism oflnsurance Medicine[END_REF][START_REF] Timmermans | Evidence-based Medicine and the Reconfiguration of Medical Knowledge[END_REF][START_REF] George | From Clinical Counting to Evidence-based Medicine[END_REF]. 1 Third, organizational studies [START_REF] Segrestin | L'Entreprise à !'Epreuve des Normes de Marché[END_REF]Brunsson & Jacobsson, 2000) as well as STS studies [START_REF] Berg | Rationalizing Medical Wbrk: Decision Support Techniques and Medical Practices[END_REF][START_REF] Bourret | BRCA Patients and Clinical Collectives[END_REF][START_REF] Cambrosio | Regulatory Objectivity and the Generation and Management of Evidence in Medicine[END_REF] have analysed standards as potentially useful coordinative devices.

In addition to these convergences, the organizational approach and some of its key concepts may offer some complementary, original insights on standardization and the bureaucratization of medicine. Drawing from seminal works byWeber, sociologists of organizations have shown that collective action is problematic, notably because actors pursue their own, often non-convergent interests, and that power has a dynamic role in relations among actors in a context of strategic interdependence [START_REF] Emerson | Power-Dependence Relations[END_REF][START_REF] Crozier | The Bureaucratie Phenomenon[END_REF][START_REF] Pfeffer | and Row)[END_REF][START_REF] Crozier | Actors and Systems: the Politics of Collective Action[END_REF]. This approach leads to an emphasis on the 'strategic interactions among a set of actors placed in a given field of action and mutually dependent for the solution of some common "problem"' (Crozier & Friedberg, 1995: 75). Taking the French oncology sector as a case, I will show that guidelines are used strategically by individual physicians and groups of physicians, and that this helps to explain some characteristics of the standardization process. This framework thus has two potential implications. First, it reveals another force propelling the development of guidelines. [START_REF] Berg | Turning a Practice Into a Science: Reconceptualizing Postwar Medical Practice[END_REF], [START_REF] Daly | Evidence-based M edicine and the Search for a Science of Clinical Gare[END_REF] and others have studied how the proliferation of guidelines resulted from medical researchers' criticism that clinical practices make limited use of available evidence from medical science. These developments have also been treated as manifestations of a new type of objectivity in the medical domain, 'regulatory objectivity' [START_REF] Cambrosio | Regulatory Objectivity and the Generation and Management of Evidence in Medicine[END_REF]. The French oncology sector provides an empirical case compatible with those theses. However, that sector shows evidence that the proliferation of different, and sometimes conflicting, guidelines that were produced at the national, regional and local levels also resulted from attempts by some physicians to improve their positions or 'jurisdiction' [START_REF] Abbott | The System of Professions[END_REF] relative to competing groups. Second, in line with other studies that clearly demonstrated how competition among professionals accompanied the development of evidence-based medicine (see, in particular, Marks, 1997), an organizational approach is helpful in underlining the dynamics and consequences of this competition. In particular, I will stress how guidelines may be used creatively and opportunistically by physicians in order to modify organizational patterns. For instance, the prominence of cancer centres and their physicians in the development and implementation of guidelines re-secured their regional and national leadership.

This point reinforces the argument made by science studies that, paradoxically, standardization does not eliminate the diversity of practices among physicians, even if it may sometimes transform those practices.

Material and Methods

The Characteristics of the French Oncology Sector

There are four main types of healthcare organization involved in cancer care in France: French comprehensive cancer centres (Centres de Lutte Contre le Cancer, CLCCs), public teaching hospitals, general hospitals and clinics.

Created in the 1920s, the 20 French comprehensive cancer centres are autonomous, publicly funded private institutions that concurrently manage research activities and treat patients within their respective regions. Each centre is directed by a physician. The 20 directors of the CLCCs collectively control the board of the National Federation of CLCCs (FNCLCC), which acts as an employers' association as well as a facilitator for collaborative scientific projects. Public teaching hospitals were created in 1958, when the Hospital Reform Act linked regional public hospitals to university medical schools (see [START_REF] Jamous | Professions or Self-perpetuated Systems? Changes in the French University-Hospital System[END_REF]. Public teaching hospitals have become the keystone of the French healthcare system. They are expected to offer the best and most advanced treatments, to train physicians and to conduct medical research for all pathologies. General hospitals and private clinics participate in cancer care by providing diagnostics and/or treatments in surgery, radiotherapy and/or chemotherapy.

The organization of cancer care in France exhibits some of the major characteristics that [START_REF] Pickstone | Contested Cumulations: Configurations of Cancer Treatments through the Twentieth Century[END_REF] described and analysed for cancer treatment in Great Britain, Sweden and the USA. There also are some distinctive features, and this paper will show that the contingent dynamics of standardization in France have been influenced by the particularities of the country's organization of cancer care.

First, competition between specialties and between healthcare organizations is particularly acute in France. There is very little reliable quantitative information describing the organization of hospital care for cancer patients, but public reports and ad hoc research generally conclude that cancer centres and teaching hospitals provide less than 40% of total cancer care, while community hospitals, either private or public, provide more than 60%. Before 2000, no national plan to regulate the organization of cancer care had been launched since the revision of CLCCs' status in 1945. Cancer centres are obliged to provide the full range of treatments for the disease, while other hospitals are free to specialize in a particular activity. Many physicians are able to participate in the treatment of cancer, and to this day, there are no legal restrictions on the administration of drugs and cancer surgery. In constrast to the situation in the USA, for instance, where medical oncologists are the only medical specialists able to prescribe drugs to cancer patients, in France every organ specialist (gastroenterologists, head and neck surgeons, lung specialists, internists) is theoretically allowed to do so.

Another major characteristic of the French cancer sector lies in the historical competition between public teaching hospitals and cancer centres, which was accurately depicted by [START_REF] Pinell | The Birth of a Scourge: The Anti-cancer Wilr in France 1890-1940[END_REF] in his study of anticancer policy in France at the beginning of the 20th century. Pinell showed that cancer centres were conceived as research-and pathology-oriented structures, under strong state sponsorship, that promoted a collaborative and comprehensive approach to cancer management. This contrasted sharply with public hospitals, which were more oriented to particular organ systems and dominated by surgeons, in line with the tradition of the Paris Clinical School. This competition for market share and the contention over the definition of the legitimate medical approach to cancer treatment continued throughout the second half of the 20th century [START_REF] Castel | lnstitutional Change as an Interactive Process: The Modernization of the French Cancer Centers[END_REF].

Data

Fieldwork was carried out in six different settings: at the national level, within the FNCLCC, which was the main producer of cancer guidelines in France during the period under scrutiny (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), and in five French administrative regions.

Fieldwork at the national level (1999)(2000)(2001)(2002) focused on the genesis of the federal guidelines project and main goals assigned to it. Data were obtained from daily informa} exchanges and semi-directed interviews with the main federal actors in charge of the project and with project directors. 1 also had access to working documents and the proceedings of meetings, where the scope of the project was discussed, decided and (re)defined. At the regional level, 1conducted nearly 300 semi-directed interviews with representatives of regulatory bodies, directors of hospitals and physicians (1999)(2000)(2001)(2002). In a specific region, for 4 years 1 was able (2003)(2004)(2005)(2006) to observe collective decision-making processes through which physicians negotiated and validated guidelines, and to interview physicians about their involvement in, and their opinions on, guideline implementation. 1also observed the therapeutic decision-making processes (N=450) of four medical staff members, focusing on the manner in which physicians referred to guidelines when they had to develop therapeutic strategies for actual patients.

A Non-unified Process Led by Professional Organizations

The development of medical guidelines in the French oncology sector was not unified: it followed several professional initiatives set forth primarily by the FNCLCC from the beginning of the 1990s that existed alongside the initiatives of medical societies and public agencies in competition for the legitimacy conferred by the scientific authority in the sector.

A Professional Initiative

Early attempts to institutionalize the production and use of guidelines in the French healthcare system began at the turn of the 1990s [START_REF] Robelet | Les Figures de la Qualité des soins. Rationalisation et normalisation dans une économie de la qualité[END_REF]. In 1987, a national agency was created to develop medical evaluation, but its actual results had been rather modest. The 1991 Health Law underlined once again the importance of evaluation in the healthcare sector (including evaluation of medical practices), but this did not lead to any significant change either. In fact, the first national standards were promulgated in 1993.These norms, however, were aimed at forbidding dangerous and costly practices rather than promoting the best ones [START_REF] Kerleau | L'Hétérogénéité des Pratiques Médicales, Enjeu des Politiques de Maîtrise des Dépenses de Santé[END_REF]. Furthermore, cancer care was not addressed by these public guidelines. The first French recommendation regarding cancer was published in 1993 by a medical society (the French Society of Mammography and Breast Pathology) and dealt with quality criteria in mass-screening for breast cancera diagnostic procedure.

From then on, cancer centres took the lead in developing cancer guidelines in France. In 1993, the board of the FNCLCC mandated some of their peers to launch a project aimed at 'harmonizing clinical practices between cancer centres, concerning diagnostic, classification, treatment and follow-up procedures' (Annual Report of the Fédération Nationale des Centres de Lutte Contre le Cancer, 1994 [author's translation]). The selected methodology to elaborate these guidelines was initially a consensus conference. But a trip to the USA, where the project leaders visited various prestigious US medical institutions, changed their minds: guidelines should rather be based on a critical review of medical literature in order to limit the impact of subjective opinions by the most reputable physicians and consequently to 'objectify' these guidelines. This project was thus explicitly conceived as a part of the emerging evidence-based medicine. From this point onwards, the scope of the project also changed its aim to defining the best practices not only for CLCCs, but also for the entire sector. It was sponsored by individual CLCCs and by the National League Against Cancer, the main patient organization in France. 2 Methodologists were recruited by the Federation. They were public health physicians who were trained to review the literature and to evaluate whether or not the final guidelines were congruent with this literature. They were meant to argue against physicians when the latter were prone to developing guidelines according to their own experience or according to the first results of the latest clinical trials rather than to a systematic review of the literature.

In addition to the methodologists, the project's leaders planned from the start to involve as many cancer centre physicians as possible in the development of guidelines. From their point of view, this strategy presented some assets: first (and quite obviously), these 1000 or so physicians represented a skilled labour force; second, their participation was conceived as a way to train them to learn and practice evidence-based medicine and to facilitate the acceptance and appropriation of guidelines. By the end of 1994, 300 cancer centre physicians had already participated, either in the task groups

Collaboration and Competition

Beginning with the publication of the first SORs, the FNCLCC involved more and more people working outside the CLCCs. At first, in 1995, an advisory board was created in addition to the executive committee, which was exclusively composed of five directors. In 1996, the executive committee welcomed one more CLCC physician, two representatives of medical societies (paediatric oncology and gynaecologic oncology) and four physicians who practiced outside CLCC. The advisory board grew to 74 members. It was decided in 1997 to create a scientific board exclusively composed of people working outside CLCC.

From 1998 to 2006, the FNCLCC published 29 clinical practice guidelines in collaboration with a medical society and more than half of the physicians who participated in the elaboration of guidelines or in the feedback process worked outside CLCC.

Despite this alliance with other actors or institutions, the FNCLCC managed the process and kept the label 'Standards, Options and Recommendations' and the (legal) responsibility for its guidelines during this period. 4 It was responsible for 81 of 148 French clinical practice guidelines (54%) that were published (see Fig. 1). Furthermore, the British Journal of Cancer, one of the most highly regarded cancer journals in Europe, also published the SORs. FNCLCC is the only French organization whose cancer guidelines are disseminated outside France. The SORs were approved by the state, and medical audits conducted by social insurance bodies used them as reference.

21%

Other French producers of guidelines were the medical societies. They published 46 sets of guidelines between 1997 and 2007. Like the FNCLCC, their guidelines concerned the management of specific cancers. Among them, the French Association of Urology (14 published guidelines -9%), the French Society of Hematology (nine guidelines) and the French Federation of Digestive Oncology (six guidelines) were the most productive . Other medical societies published only one guideline during this period.

Guidelines by the National Agency were of a different kind: they corresponded either to recommendations for prevention and screening procedures or the evaluation of new techniques, or they answered precise questions (for example, 'Can initially non-resectable hepatic metastases be made resectable? ').

Diversity of the Implementation Processes at the Regional Level

A recent study funded by the French National Cancer Institute confirmed the results of two previous surveys conducted by the FNCLCC :the SORs were generally considered by physicians as the most reliable guidelines for oncology. However, the physicians who worked in CLCCs or who devoted more than one-half of their activity to cancer patients were more familiar with these guidelines and utilized them more frequently.

Nonetheless, the SORs were considered as tools for everyday practice by a few practitioners who worked inside teaching hospitals or cancer centres. Cancer centres thus created voluntary and cooperative networks for the elaboration and implementation of regional treatment protocols adapted to the characteristics and resources of the local healthcare system. This entailed initiating and monitoring the discussion process at the regional level. Federal review monographs were thus transformed into decision-making algorithms and into specific recommendations of one or another remedy chosen from among several scientifically appropriate treatments. In some regions, the cancer centre created a network without involving the regional teaching hospital. As a result, these teaching hospitals organized opposing networks. Besides these regional networks, some physicians who specialized in the treatment of specific organs -mainly urologists, gastroenterologists, surgeons, lung specialists and haematologists -stated that they used the guidelines of medical societies rather than the SORs.Thus, while French physicians generally considered the SORs to be the standard reference guidelines and appreciated them for their scientific reliability, in practice they referred to differing and even contradictory guidelines [START_REF] Fervers | Evaluation de la place des Recommandations de Pratique Clinique et Référentiels en cancérologie dans la pratique clinique[END_REF].

Development of Guidelines as a Collective Strategy for Intra-professional Legitimacy

The specific dynamics of this movement -its initial impulse and the diversity of involved organizations at the national and regional levels -contributed to the specific organization of cancer care in France. In particular, the rivalry and competition between specialties (pathology-centred specialists vs. organcentred specialists) and between hospitals influenced this development.

The Reinstatement of Cancer Centres as Dominant Actors through the Development of Guidelines

There were several reasons for the launch of the guidelines programme by the FNCLCC. On one hand, the development of the guidelines was in line with a process described in other studies as an intra-professional movement favouring a more 'scientific' basis for medical knowledge [START_REF] Berg | Turning a Practice Into a Science: Reconceptualizing Postwar Medical Practice[END_REF][START_REF] Timmermans | Evidence-based Medicine and the Reconfiguration of Medical Knowledge[END_REF][START_REF] Cambrosio | Regulatory Objectivity and the Generation and Management of Evidence in Medicine[END_REF]. On the other hand, there were instrumental reasons for pursuing such a programme: the CLCCs' directors expected to take advantage of this programme to re-secure their role at the national level and at the apices of regional hierarchies.

The traditional collective identity of French cancer centres and the evolution of their position in the French oncology sector explain why their physicians first became involved in the development and dissemination of guidelines. These guidelines have been considered as tools for reinstating themselves as scientific leaders in the sector and as partners for other physicians. This project was the keystone for an ambitious reform programme conducted by the FNCLCC. This programme also consisted of the development of research activities, an accreditation programme and the negotiation of new professional statutes for employees. lt was a direct response to increasing competition for the CLCCs and to critiques by other stakeholders in the sector (Castel & Friedberg, 2004). In particular, in 1993 a public report (Inspection Générale des Affaires Sociales, 1993) raised the question of maintaining cancer centres, as they were considered to be costly and their added value in the treatment of cancer could not be ascertained. The group of physicians who developed this programme shared a number of distinctive features. First, their medical specializations contrasted with those of the previous directors of the centre that they were heading. Three of these directors were the first medical oncologists to be appointed as heads of their cancer centres, while the fourth was the first radiotherapist. The four followed three surgeons and a pathologist as directors. In sum, the four had some common, disciplinary interests to defend, as surgery was the still dominant treatment technique in cancer care, and so they were more open than others to the rise of chemotherapy and its implications for the position taken by the CLCCs. Second, the members of this group of reformers had been actively and very successfully involved in research activities, a fact that strongly contrasted with other directors of the National Federation's board. In particular, the three medical oncologists spent some time in the USA, where they had been appointed research fellows at some of the most prestigious American institutions at which new treatments had been developed through experimental research and multi-centre clinical trials (the National Cancer Institute, and the Fred Hutchinson Cancer Research in Seattle, WA).

In 1993, the instigator of the guidelines project was a paediatric oncologist, the director of a cancer centre located in a very competitive region. His motives in developing guidelines were fourfold. First, he shared with his American peers the goal of implementing state-of-the-art practices in every hospital (see [START_REF] Berg | Turning a Practice Into a Science: Reconceptualizing Postwar Medical Practice[END_REF][START_REF] Daly | Evidence-based M edicine and the Search for a Science of Clinical Gare[END_REF], and he could have qualified, using Marks' (1997) expression, as a 'therapeutic reformer'. Indeed, he could not abide by the heterogeneity of the treatments that were prescribed by physicians in his centre as this would imply unequal treatment of patients. He was all the more sensitive to this issue given that the international community of paediatric oncologists had been involved in the question of harmonizing their practices for many years (Castel & Dalgalarrondo, 2005). Second, he realized that this heterogeneity was an obstacle to the regional legitimacy of his centre: physicians from other hospitals might question the quality of the advice that CLCC physicians offered them.

There have been two initial reasons to launch this project. The first one is an inner one. We, paediatric oncologists, treated lymphoma with a specific protocol and we saved 75% of the children. In another service, physicians treated adults with lymphoma with another protocol and saved only 25% of patients. Thus, the poor patient was 25% likely to survive if he was over 16, whereas children under 16 were 75% likely to survive. And 1 did not judge it justifiable that patients be treated differently from one service to another ....The second reason is an anecdote. Dr X [a head of service in a big public general hospital] called me once and told me: 'I called your centre to ask if it was possible to prescribe birth contrai pills to a woman with breast cancer and 1had three different answers.'Then, he told me: 'As long as you are not able to agree with each other -or at least to argue why you disagree -we will not consider you as the leading hospital.' (Interview with the director of the cancer centre, 1999; author's translation) Third, this director hoped that the development of guidelines could be used to reshape (and improve) the relationships between his centre and other general hospitals. His centre should appear to other hospitals as a facilita-tor for treating the more frequently occurring cancers, as a scientific reference centre that could help them treat more complex and rare cancers, and a centre that they could use for referring patients to clinical trials or for specific care.

Physicians who work in other hospitals want us to let them develop their business . ... Our answer is the thesaurus [that is, the treatment protocols], outside consultations ... it is an openness which leads us to advise a treatment for patients we do not necessarily see. It is an evolution you know well. (Presentation to the medical board of the cancer centre, 1993; author's translation) Last, in the same presentation he said that guidelines might be mentioned as a reason to convince regulatory bodies to pay for new, expensive treatments. 5 Other directors were soon convinced of the strategic opportunities furnished by this project for CLCCs. At the national level, they were well aware that it might contribute to re-establishing their legitimacy for the public authorities and the French medical community. At a time when concern for quality in the healthcare system was rising [START_REF] Setbon | La Qualité des Soins, Nouveau Paradigme de l'Action Collective?[END_REF][START_REF] Robelet | La Profession Médicale Face au Défi de la Qualité: une Comparaison de Quatre Manuels de Qualité[END_REF][START_REF] Robelet | Les Figures de la Qualité des soins. Rationalisation et normalisation dans une économie de la qualité[END_REF], CLCCs would be the hospitals that set the example.

At the rime [in 1993, at the beginning of the project], the Social Security agency was about to elaborate guidelines. ...Tuen, what was our usefulness if, as oncologists, we were not able to produce cancer guidelines? We thus decided together: 'We will produce guidelines by ourselves and respect them before we are forced to do so by someone else.' ... Furthermore, our oncologists used to say that they were the best. They had to prove it [in producing guidelines]! (Interview with a director, 2002; author's translation)

The SORs were preeminently seen by the directors as a way to set the rules in the oncology sector. Teaching hospitals were particularly threatening to them. From the 1980s onwards, teaching hospitals claimed that cancer centres were not useful anymore, since they had the same missions in the field of cancer care. The teaching hospitals further argued that their physicians, specialized in organ treatments and at the forefront of clinical research, were more qualified to treat (and cure) cancer and to teach other physicians how to do so. In this struggle for legitimacy, the directors conceived of guidelines as a way to reaffirm the usefulness of CLCCs alongside the teaching hospitals. But the guidelines were also a tool to defend the medical approach and the organization of cancer care that CLCCs had developed [START_REF] Pinell | The Birth of a Scourge: The Anti-cancer Wilr in France 1890-1940[END_REF] and were very proud of. CLCC was an organization based on the participation of every medical specialist in the decision-making process related to a patient's treatment strategy -a multidisciplinary approach. It differed from teaching hospitals, which tended to promote another model in which mastery of the initial decision was given to the organ specialist (and mainly to the surgeon). It therefore cornes as no surprise that one of the first guidelines elaborated by the FNCLCC was entitled 'Standards, Options and Recommendations Concerning Good Practices in the Multidisciplinary Organization of Cancer Care' (Chardot et al., 1995). At the regional level, the directors' expectations were congruent with those of the project leaders: they intended to use the SORs to restore the leadership of their centre and to improve its relationships with general (private and public) hospitals. But they also had specific strategic uses of the SORs depending on the local organizational context. For instance, for some directors who had decided to enhance collaboration with the regional teaching hospital, the SORs helped them to initiate a dialogue between their physicians and those who worked in the teaching hospital. In one region, the elaboration of a common language and common therapeutic attitudes subsequently allowed a new division of cancer care between these two hospitals to be established. In other regions, the directors hoped that the diffusion of guidelines would facilitate the treatment of common cancers by general hospitals, allowing CLCC physicians to concentrate on complex tasks. In contrast, in some sectors the SORs were a tool to restrict the entry of newcomers.

When the organization of cancer care was discussed at the regional level [with regulatory bodies and hospital representatives] two years ago, we had a clear idea about which hospitals we wanted to work with and with which we did not. We came to the discussions with the SORs, saying: 'These are the best practices in oncology and we cannot sel! off oncology. Thus, only hospitals which are able to comply with the SORs may care for cancer patients.' If you refer to some rules which you do not have written down and which describe what has to be done, it defuses a bomb. Then, we succeeded in selling the ideas of a multidisciplinary organization of cancer care and a unique regional medical record . ... It is not al! achieved, but .... People have made headway. We may notice that some hospitals have given up the idea of developing oncology, others have grown bigger. (Interview with a vice-director of a CLCC, 2001; author's translation)

Although the SORs were used to achieve various specific results, at their core the guidelines represented for CLCC directors a tool to the reorganization of cancer care in their regions. This was a major motive for adopting the project.

Counter-reactions

As noted earlier, public authorities delegated cancer guidelines to the FNCLCC and approved the SORs, thus reinstating CLCCs as legitimate organizations in the French oncology sector. Medical societies then stepped in and became involved in the development of cancer guidelines. Sorne of them collaborated with the FNCLCC and others produced their own guidelines. These different attitudes were partially linked with the specific relationships that oncologists had developed previously with the different organ specialties.

The medical societies that have been the most prolific producers of guidelines are dominated by organ specialists, who traditionally oversee the care of particular cancers at the expense of oncologists. They consider oncologists to be merely 'sub-contractors'. Indeed, urologists, gastroenterologists and haematologists perceived oncologists as competitors. For instance, urologists usually consider surgery to be the best treatment against localized and locally advanced prostate cancers, even though some studies have concluded that surgery and radiotherapy have equivalent risks as treatments. For them, radiotherapy must be an option when surgery is not possible. The respective place of these two treatments for prostate cancers remains controversial [START_REF] Hakenberg | Treatment of Locally Advanced Prostate Cancer: The Case for Radical Prostatectomy[END_REF]. In the same vein, gastroenterologists consider themselves to be more qualified than oncologists to prescribe drugs for gastrointestinal cancers, since they understand the workings of the corresponding organs better and thus are able to develop treatment protocols accordingly. However, even if they more or less openly criticized the FNCLCC for trying to lead the development of guidelines at the national level, all these societies could not help but to attest to the importance of the SORs.

It is true that there have been conflicts between oncologists and urologists. Things are changing, leading to fewer conflicts. But this remains very much 'physician-dependent' . .... But there is still a problem: the FNCLCC still tends to think that cancer centres embody cancer care.We answer that they are only one actor amongst others. ... The methodology that the French Association of Urology is using to produce guidelines is becoming more and more credible. We are trying to elaborate them according to the level of evidence, like the SORs. (Interview with a member of the board of the French Association of Urology, 2003; author's translation) Unlike the first medical societies, the physicians that agreed to participate in the SOR project happened to be either oncologists, or organ specialists who were used to working with oncologists. Since the 1970s, the French Society of Pediatric Oncology had been composed of physicians from cancer centres and teaching hospitals who had developed common research and treatment protocols [START_REF] Castel | La Dimension Politique de la Rationalisation des Pratiques Médicales[END_REF]. In the French Society of Gynecologic Oncology, gynaecologists and oncologists have collaborated for a long time, since breast cancer was one of the first cancers that was amenable to treatment with a multidisciplinary approach -combining surgery, radiotherapy and medical treatment [START_REF] Pickstone | Contested Cumulations: Configurations of Cancer Treatments through the Twentieth Century[END_REF].

However, even if the organization of cancer care influenced the development and implementation of guidelines, it did not determine them. Specialists who once were competitors learned to work together on the development of guidelines. For instance, the French Society of Dermatology finally agreed to co-sign two guidelines with the FNCLCC, although they had been reluctant to do so for a long time. The French Federation of Digestive Oncology also joined the SOR project 3 years ago, after it had published six guidelines itself. One hypothesis for this development lies in the legitimacy that the SOR project gained in the French oncology sector, so that it was difficult for an (isolated) medical society to continue this activity in parallel. Another hypothesis is that the regulatory capacity of evidence-based medicine entailed an inherent reflexivity among participants and resulted in the production of conventions and concerted programmes of action [START_REF] Cambrosio | Regulatory Objectivity and the Generation and Management of Evidence in Medicine[END_REF].

Individual Authority and Guidelines

In the French oncology sector, physicians tend to hold a positive opinion of guidelines [START_REF] Castel | Quand les Normes de Pratiques Deviennent une Ressource pour les Médecins[END_REF][START_REF] Fervers | Evaluation de la place des Recommandations de Pratique Clinique et Référentiels en cancérologie dans la pratique clinique[END_REF]. They consider that guidelines limit the risk of patients and hospital managers mistrusting the quality of medical practices, and they appreciate the guidelines being developed exclusively by professionals (including those approved by public authorities) and their not being used by public authorities to sanction physicians (Castel & Merle, 2002). One may also hypothesize that this positive opinion is due to the specificity of the pathology and the historical organization of its management, 6 but to pursue this hypothesis would necessitate a systematic comparison with the development of guidelines for other pathologies. I will argue in this section that participation in the development and implementation of guidelines may also be the result of an individual strategy by physicians to increase the visibility of their specialization in cancer care and in the medical community, and thus to have greater control of patients' 'trajectories', which refers 'not only to the physiological unfolding of a patient's disease but to the total organization of work clone over that course' (Strauss et al., 1985: 8). In brief, intra-professional legitimacy is also at stake for the individual practitioner, which partly explains why some become involved in the elaboration and implementation of guidelines while others do not.

The Interests of Cancer Centre Physicians in the SOR Project

The SOR project probably would have failed if the physicians who directed CLCCs had not convinced 'rank-and-file' oncologists to participate. As noted above, nearly two-thirds of the medical community enrolled within a few years. The CLCC physicians we interviewed between 1999 and 2002 did not criticize either the developmental process of the SORs or the quality of the final documents. Instead, they generally expressed pride in their participation. For instance, in 1995, seven of the most significant inter-CLCC scientific groups (specializing in gynaecological tumours, breast cancers, gastrointestinal cancers, genetic oncology, infectious diseases in oncology, statistics and radiology) prominently included participation in the SORs in their annual reports.

There are three reasons for this success. The first is an institutional: CLCC physicians were aware that the oncology sector was becoming more competitive and thus increasingly threatening for them. They believed that the SORs could contribute to re-establishing cancer centres as leaders in the French oncology sector.

The SORs are a wonderful tool and only CLCCs are able to produce itthanks to our multidisciplinary culture. We receive great credibility when we publish a SOR. ... When we write such texts, we become incontestable in the sector. (Interview with a radiotherapist, 2000; author's translation) Moreover, the traditional multidisciplinary organization inside CLCCs facilitated the acceptance and support of this project by the participating physicians. They were also more likely to accept a formalized (collective and multidisciplinary) regulation of their practices.

The guidelines are part of a global evolution, but this does not represent a revolution for us. For other hospitals, it may be a cultural revolution ... : the systematic reference to a document for therapeutic decision-making and the multidisciplinary organization of care are not innate; it requires a specific organization and structure. (Interview with a CLCC surgeon, 2002; author's translation)

The second reason for the success is related to the management of this project, which was not intended to have a top-down organization. On one hand, the whole medical community was invited to get involved. It was not limited to opinion leaders. Furthermore, each guideline had to be validated by every CLCC medical committee (composed of all physicians who worked inside the centre) before it could be published. On the other hand, reformers presented this project to the physicians as a way to improve their practices rather than as a coercive means to control them. Medical evaluations were intended to assess the conformity of medical practices with the SORs, but no sanction was considered.

The third reason is that physicians believed that the SORs helped them in their daily practices. On one hand, their involvement in the development and dissemination process contributed to their hyper-specialization (and authority) with certain cancers. Belonging to a national task force responsible for a SOR enhanced or consolidated a physician's reputation for treating the corresponding cancer (similar to publishing the results of randomized clinical trials in leading medical journals). In the same vein, in order to adapt and implement the SORs, the management of a task force at the regional level contributed to the regional authority of this physician: not only could the physician make clear during discussions that he or she was well-versed in the literature and aware of the latest clinical trials, but at the same time the physician could also demonstrate to regional colleagues an inclination to help them -thus exhibiting a kind of altruism.

[A medical leader] is someone who works a lot and who works well. We may evaluate this through his care for the patients we refer to him. But he is also someone who participates in task groups and in protocols. And he is someone who knows how to share his knowledge. The number of publications is one criterion but it is not the only one. What counts more is showing one's intention of working ... and on the way one is trying to be acknowledged as a leader. There is also the human touch. (Interview with an oncologist in a general hospital, 2003; author's translation) Because of a significant increase in the number of papers related to randomized clinical trials in the early 1990s, it was difficult for even CLCC physicians to be well informed on current treatments for every cancer. Given the fact that most of them specialized only in certain kinds of cancers, they tended to use the SORs as a resource for novel scientific information about the cancers with which they were less familiar.

I am an oncologist, but I do not know 10% of ail the decisions to take in oncology. We are hyper-specialized. For instance, I am specialized in prostate cancer. But when it departs from your hyper-specialization, it becomes very complicated. Guidelines will be referred to by physicians when the case departs from their specialty. (Interview with a radiotherapist, 2000; author's translation)

In particular, cancer centre physicians were interested in using the SORs for external counselling. When they had to give advice to peers on cancers in which they were not specialized, the SORs constituted a precious resource.

Opportunistic Uses of Guidelines

Other physicians might also perceive the strategic advantage of participating in the regional process of implementing guidelines. Organ specialists who wanted to specialize further in oncology, or oncologists who worked in public or private general hospitals and who therefore had to be trusted by surgeons, might choose to participate in the regional implementation process in order to acquire local credibility -to convince colleagues who might refer patients to them that they were competent to prescribe the correct treatments. There is no available study that compares overall survival rates among different hospitals in France. A doctor's reputation therefore rests on other (social) mechanisms, such as participation in clinical research, which can allow a physician to acquire a distinctive reputation through publication or other communications. Participation in oncology networks in France -which develop guidelines and promote the creation of multidisciplinary (and sometimes multi-hospital) medical staff for making therapeutic decisions -can be viewed as another medical strategy for restoring medical authority. Physicians who were interviewed said they participated in that process in order to increase their knowledge, to appear competent when talking with their peers and to acquire a good reputation.

Participating in a regional task force for implementing the SORs enabled physicians who worked in general healthcare organizations to have privileged and persona! access to the knowledge and experience of their aca-demic7 counterparts. Guidelines facilitated the sharing of specialized knowledge, so that 'rank-and-file' physicians depended less on the persona! advice of their illustrious colleagues about the most frequent types of cancers. We may then take [START_REF] Segrestin | La Normalisation de la Qualité et !'Evolution de la Relation de Production[END_REF] analysis of the International Organization for Standardization (ISO) norms as applicable to guidelines as well: the 'logic' of both kinds of tools consists of sharing knowledge which previously had been mastered only by experts.

If someone wants to practice traditional surgery, [the work on guidelines] is not that important. But if someone wants to specialize in oncology, then .... It is changing so fast! Nobody is able to attend all scientific meetings; nobody is able to read the whole published literature. ... Ifsomeone wants to 'hyperspecialize', he has to know up-to-date treatments and nobody can do it on their own. (Interview with a private surgeon, 2003; author's translation) Such participation was a resource for physicians in their efforts to gain greater control over the management of patient 'trajectories' in both of Strauss' senses of the course of illness and the temporal organization of medical work [START_REF] Strauss | The Social Organization of MedicalWbrk[END_REF]. This allowed them to intervene more intensively in the work of their colleagues.

First, they could acquire greater legitimacy than other physicians. Sorne found the 'network' label useful for convincing their patients and peers (general practitioners, surgeons and diagnostic physicians, among others) that they were as competent as, say, physicians with academic training in the subject. Such authority relied, then, more on local, collective norms than on individual competence. By contrast, organ specialists (gastroenterologists, surgeons, and so on), for whom tending to cancer patients did not represent a major part of their activity, did not get involved in networks.

The network is useful to attest my competencies. 1 decided to adhere to it as soon as it began . ... Surgeons, when they send me a patient, know that some regional standards exist. Thus, 1 am writing in the medical record: 'standard of [the regional network]'. It legitimizes my decision. They know that every patient is treated in the same way. (Interview with a medical oncologist, 2003; author's translation) Second, during task group discussions, they had the opportunity to break the monopoly over cancer care held by the academic physicians. The first social mechanism was negotiation, as [START_REF] Timmermans | The Gold Standard. The Challenge of Evidencebased Medicine and Standardization in Health Gare[END_REF] have shown: the organ specialists negotiated with academic physicians so that guidelines did not prescribe treatments that were too complex and that could not be implemented by general facilities (clinical trials, intensive chemotherapies, up-to-date diagnostic examinations, and so on). The second mechanism was trust: during discussions, the organ specialists got a chance to convince their (specialized) colleagues that they were competent and might even have some expertise. For example, some academic physicians who were interviewed said that before this process they tended to mistrust their colleagues who worked in general healthcare organizations, believing that they were insufficiently competent. However, after the discussions, they said they were more inclined to allow such physicians to take care of patients who suffered 'standard' cancers (such as colon cancer or breast cancer) or even to re-assign such patients to them.

This allowed me to meet some physicians who worked in general hospitals and whom 1had not known before. It helped me to avoid certain prejudices. In the medical world, it is terrible how fast we label people! 'The private sector does not think anything but money!' 'The public sector does not do anything at ail!' But, when we came to know each other, we realized that people share a common interest: the patient! And we also realized that everybody worked hard. (Interview with an academic Jung specialist, responsible for a regional task group, 2003; author's translation) Last but not least, the guidelines constituted a robust argument for physicians, so that they could try to change the behavior of their peers and influence the management of patients. For instance, during multidisciplinary staff meetings, physicians were able to argue that a therapeutic decision was not 'evidencebased' and thus try to change it, even if the patient was not under their care. Physicians who wanted to propose a 'non-conforming' treatment had to justify it. Another example lies in the changing relationships between surgeons and radiotherapists in an area in which treatment protocols had become broad. Surgeons grumbled about the growing encroachment of radiotherapists on their autonomy. Radiotherapists dared to ask them to perform new operations when surgical margins were insufficient to meet the guidelines they had available. Another recurrent example had to do with relationships between diagnostic specialists and clinicians: the latter were more prone to use guidelines to frame their colleagues' activities in terms of the timeliness and quality of their examination reports.

[The regional protocols] make clear that 1am not manie or obsessive when 1am asking them for some quality criteria: these criteria are written in the guidelines! For example, 1must have exam results in pathology or in radiology fifteen days later. As for pathologists, when we ask them to write some details, it is not because we are maniacs, it is only because it has to be that way. (Interview with a private surgeon, 2003; author's translation) Of course, this does not mean that physicians were compelled to obey their colleagues if they relied on guidelines. Other types of authority still existed in the sector. For example, when adapting a protocol, physicians could invoke the uniqueness of every therapeutic relationship. Academic physicians could rely on charisma or persona! prestige, and some of them even refused to participate in networks that implemented guidelines. They preferred to organize frequent meetings in which they gave persona! advice on specific cases that were brought by non-specialized physicians. Nonetheless, our observations made clear that rational-legal authority [START_REF] Weber | Economy and Society[END_REF][START_REF] Weber | Economy and Society[END_REF]: 215-23) is becoming dominant in the French oncology sector. More physicians find it increasingly legitimate to justify therapeutic decisions and advice by reference to the guidelines and medical literature. Furthermore, guidelines facilitate an increasing 'lateral control regime' [START_REF] Lazega | Rule Enforcement among Peers: A Lateral Contrai Regime[END_REF] among physicians. In contrast to the previous situation when physicians had limited opportunities to meet with and evaluate one anothers' work [START_REF] Freidson | Processes of Contrai in a Company of Equals[END_REF][START_REF] Crozier | The Bureaucratie Phenomenon[END_REF], guidelines represent a device that increases interdependency among physicians and acts as a frame of reference with which to judge colleagues. This analysis thus seems compatible with the results of some medical, quantitative studies on the impact of cancer guidelines on medical practices. While some national reports by the French Health Insurance complained about a global, low compliance rate of practices with national cancer guidelines, and especially with the SORs (Caisse Nationale d'Assurance Maladie des Travailleurs Salari, 2003, 2005), a set of medical audits conducted in two regions argued that a local implementation strategy might increase the degree of compliance with guidelines [START_REF] Ray-Coquard | A Controlled "Before-After" Study: Impact of a Clinical Guidelines Programme and a Regional Cancer Network Organization on Medical Practice[END_REF], 2005). I hypothesize that this greater compliance is due to an increase in the local interdependency and mutual control that the implementation process provoked among the involved practitioners.

Conclusion

Medical standardization not only alters relational dynamics between physicians and non-physicians (patients, hospital managers and regulatory bodies), but it may also alter relationships among physicians themselves. In line with the reports of [START_REF] Timmermans | The Gold Standard. The Challenge of Evidencebased Medicine and Standardization in Health Gare[END_REF] and [START_REF] Cambrosio | Regulatory Objectivity and the Generation and Management of Evidence in Medicine[END_REF], this case study shows that standardization improves relationships among physicians (for instance, through task groups) and influences the development of shared conventions that facilitate such interpersonal exchanges. Standardization in the medical field allows for an improvement in relationships between actors through mechanisms of collective learning, much as in the industrial sector (Segrestin, 1997; Cochoy et al., 1998; Brunsson & Jacobsson, 2000).

This study of standardization in French oncology has also shown the value of taking political considerations into account when studying the development of standardized guidelines. Timmermans and Berg (2003: 21) also proposed 'a study of the politics of standardization in practice', but they did not define power, nor did they study the concrete processes of negotiation through which some physicians try to use standards to foster collaboration with others for their own benefit. Here, I considered an interactive and strategic concept of power, which is a basic ingredient of exchange relations between actors placed in a context of strategic interdependence [START_REF] Crozier | The Bureaucratie Phenomenon[END_REF]Boudon & Bourricaud, 1982;[START_REF] Chazel | Pouvoir[END_REF]. Power in this conception is the unequal and negotiated exchange of capacities for action through which every member tries simultaneously to constrain other members of an organization, in order to satisfy expectations and avoid being constrained by the others [START_REF] Crozier | Actors and Systems: the Politics of Collective Action[END_REF]Friedberg, 1997). Strategy and resources are, therefore, two key ideas related to this concept of power. In the case of French oncology, I established that standards were used as strategic resources by professional actors at the expense of others in order to improve their position or 'jurisdiction' [START_REF] Abbott | The System of Professions[END_REF]. The aims of such strategies were: (1) maintaining a sufficient volume of activity; and

(2) increasing control over therapeutic decisions. CLCCs and oncologists benefited the most from these standards. This may be explained by the fact that they had more resources at their disposai to develop guidelines (in particular, their orientation toward clinical research and their traditional, multidisciplinary organization). However, as I also mentioned, some organ specialists were also able to use guidelines. According to this theoretical perspective on power, even actors placed in a favourable situation could not eliminate the capacity of other actors to resist. This explains why negotiations took place at every level of analysis: national, regional and local. By placing concrete exchange and bargaining relations at the core of the analysis, and showing how social control is continually challenged and (re)produced, the study demonstrated that standardization is not necessarily incompatible with local specificities and variations, and may even enhance them (see also Timmermans & [START_REF] Berg | Rationalizing Medical Wbrk: Decision Support Techniques and Medical Practices[END_REF][START_REF] Zuiderent-Jerak | Preventing lmplementation: Exploring Interventions with Standardization in Healthcare[END_REF]. 1. While there is much to say about the ambiguity of guidelines for patients and their representatives (for a synthesis of these issues, see [START_REF] Berg | Rationalizing Medical Wbrk: Decision Support Techniques and Medical Practices[END_REF] and [START_REF] Timmermans | Evidence-based Medicine and the Reconfiguration of Medical Knowledge[END_REF]), the issue falls beyond the scope of this paper. Whereas some proponents of evidence-based medicine argue that guidelines may improve the appropriateness of healthcare practice, other actors fear that they may hinder the consideration of therapeutic alternatives that would be more appropriate to the specific needs of the individual patient. Sociologists diverge in their opinions as to whether protocols reinforce or weaken professional authority. 2. The alliance between cancer centres and the League Against Cancer has historical and institutional roots, as both were created at the same time and by the same actors (see [START_REF] Pinell | The Birth of a Scourge: The Anti-cancer Wilr in France 1890-1940[END_REF]. At the local level, CLCC directors are frequently also presidents of the professional associations for their specialities. In 1997 at the national level, the former president of the Federation became president of his speciality association, but this alliance was also due to congruence between the strategic development programme of the association and the reform programme of cancer centres [START_REF] Castel | lnstitutional Change as an Interactive Process: The Modernization of the French Cancer Centers[END_REF]). 3. These guidelines are called 'Standards, Options and Recommendations' (SOR) since they are classified into three categories. A clinical stance is called a 'Standard' when there is unanimity concerning its benefits, its inappropriateness or its potential danger. An 'Option' is so-called when a majority of physicians agrees with the benefits, inappropriateness or dangers of a specific stance. 'Recommendations' represents a choice by experts from different options. Each category is explicated by a degree of evidence, depending on the available scientific data. 4. Since mid 2008, the situation has changed: the French National Cancer Institute (NCI) is now the administrator of the SOR project. However, as the website mentions (<www.sor-cancer.fr/>), the SORs were created by the FNCLCC, which still maintains a decisive role in the project since it is one of the three members of the leading consortium, together with the French NCI and the National League Against Cancer. 5. In the same vein, Berg and colleagues (2000) showed that guidelines had been tools for insurance physicians in the Netherlands -used to restore the legitimacy of their practices, which had been criticized by non-physicians. 6. To mention two characteristics: (1) oncology is a domain that from its beginning was 'science rich' [START_REF] Pinell | The Birth of a Scourge: The Anti-cancer Wilr in France 1890-1940[END_REF] and was especially closely linked with the development of clinical research [START_REF] Cambrosio | Rationalisation et Médecine des Preuves en Oncologie: Quelques Remarques à Propos des Pratiques Biomédicales (Commentaire)[END_REF][START_REF] Keating | Cancer Clinical Trials: The Emergence and Development of a New Style of Practice[END_REF][START_REF] Pickstone | Contested Cumulations: Configurations of Cancer Treatments through the Twentieth Century[END_REF] so that oncologists were probably more apt to accept 'a shift from pathophysiology to epidemiology with guidelines' (Timmermans & Kolker, 2004: 177); (2) the increasing number of clinical trials for cancer remedies legitimates the need for tools to synthesize the evolution of medical knowledge. 7. By 'academic physicians', I mean doctors working in hospitals whose missions are research and teaching, such as teaching hospital and cancer centre physicians.

  FIGURE 1Producers of French cancer guidelines(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)

NotesI

  would like to thank Alberto Cambrosio, Peter Keating, Thomas Schlich and George Weisz for the opportunity to present an earlier version of this paper at their conference, 'The Institutions of Objectivity in Medicine: Informai and Formai Modalities of Regulation', at McGill University (Montreal), 19-22 April 2007. I also thank Charles Rosenberg for his useful comments on that occasion, and Michael Lynch and the anonymous reviewers whose comments and suggestions helped me to clarify my arguments. I thank Erhard Friedberg for his helpful advice during this research, and Connie Chow and Martha Zuber for their editing assistance.

TABLE 1

 1 Participation of medical societies in the FNCLCC's guidelines(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)

	Medical society	Number of guidelines
	French Dermatology Society	2
	French Society of Pediatric Oncology	6
	French Federation of Digestive Oncology	2
	French Society of Gynecologic Oncology	4
	Society for the Study and the Treatment of Pain	5
	French Society of Pneumology	2
	Study Group of Lymphomas	2
	Others*	6
	Total	29
	*French Sarcoma Group, French-speaking Society of Entreal Nutrition, French Society of
	Pathology, French Association of Urology, French-speaking Society of Brain Surgery, and
	French Society of Nuclear Medicine.
	(which developed the clinical practice guidelines) or in the feedback process
	(consisting of comments on the first versions of the guidelines). Six hundred
	physicians had taken part in the project by 1998.The first documents, called
	'Standards, Options and Recommendations' (SOR), were produced in
	1995. They consisted of long monographs (about 200 pages) and of sum-
	maries published by the main French cancer journal Bulletin du cancer. 3


Christian K Dang
email: c.dang@ucc.ie

Mark O Gessner

Eric Chauvet

Influence of conidial traits and leaf structure on attachment success of aquatic hyphomycetes on leaf litter

Keywords: aquatic hyphomycetes, attachment, conidial shape, decomposition, leaf litter, stream

Attachment of conidia on leaves is a critical first step in the life cycle of aquatic hyphomycetes in streams. In a first series of microcosm experiments, attachment success of three common aquatic hyphomycete species differing in conidial shape (compact, filiform and tetraradiate) was determined on two leaf species, black alder and downy oak. Fungal species identity and leaf surface structure significantly affected conidial attachment after 24 h. The lower sides of oak leaves with extensive tufts trapped 2.4-8.8 more conidia than the upper sides of oak leaves and both sides of alder leaves. In a second experiment with seven fungal species, attachment success of two species with tetraradiate conidia was much greater than that of two other tetraradiate and three compact conidia, which all had similar attachment success. The species with the largest spores was also the most successful, but this pattern was not consistent across the size range of tested conidia. These results highlight the importance of leaf surface structure, possibly conidial shape and size and additional properties of aquatic hyphomycete conidia in determining attachment success on leaves and they point to the potential role of these factors in structuring fungal communities on decomposing leaves in streams.

INTRODUCTION

Aquatic hyphomycetes are important drivers of leaf litter decomposition in streams, a fundamental ecosystem process in forested catchments (Ba ¨rlocher and [START_REF] Kendrick | Dynamics of the fungal population on leaves in a stream[END_REF], Suberkropp and Klug 1976, Gessner and Chauvet 1994[START_REF] Hieber | Contribution of stream detrivores, fungi, and bacteria to leaf breakdown based on biomass estimates[END_REF][START_REF] Pascoal | Contribution of fungi and bacteria to leaf litter decomposition in a polluted river[END_REF]. Colonization of leaves and other substrates by aquatic hyphomycetes may occur through three pathways: by direct contact as a result of hyphal outgrowth from a colonized leaf touching another leaf or piece of wood; at a distance by either detached hyphal fragments (Park 1974, Knudsen and[START_REF] Knudsen | Modeling growth and dispersal of fungi in natural environments[END_REF] or asexual spores called conidia (Read et al 1992) that land on a leaf surface. The last mechanism appears to be the predominant one to colonize distant leaf patches (Sridhar and Ba ¨rlocher 1997).

Once settled on a substrate, conidia of aquatic hyphomycetes germinate within hours, or less (Read et al 1992;[START_REF] Au | The role of mucilage in the attachment of conidia, germ tubes, and appresoria in the saprobic aquatic hyphomycetes Lemonniera aquatica and Mycocentrospora filiformis[END_REF], by developing one or more germ tubes that generally form appresoria on the substratum (Read et al 1992). These structures ensure a solid adherence to the colonized surface (Webster and Davey 1984) and subsequently permit the fungus to penetrate the plant tissue [START_REF] Hatzipapas | Spore germination and appressorium formation in the entomopathogenic Alternaria alternata[END_REF]. At the beginning of colonization, hyphal extension in leaf tissue can be rapid, with growth rates measured in leaf litter of up to 0.72 d 21 (Suberkropp and Weyers 1996, Gessner and Chauvet 1997[START_REF] Pascoal | Contribution of fungi and bacteria to leaf litter decomposition in a polluted river[END_REF]. In contrast to most other fungi, aquatic hyphomycetes typically start to produce and release conidia soon after initial colonization of a new substrate, and the high sporulation activity of up to 7000 conidia produced per mg leaf dry mass per day [START_REF] Ba ¨rlocher | On the ecology of Ingoldian fungi[END_REF][START_REF] Suberkropp | Relationships between growth and sporulation of aquatic hyphomycetes on decomposing leaf litter[END_REF], Gessner and Chauvet 1994, Gulis and Suberkropp 2003, Pascoal et al 2005) results in conidial concentrations in headwater streams that can reach several thousands per liter during autumn leaf fall [START_REF] Webster | Experiments with spores of aquatic hyphomycetes I: sedimentation and impaction on smooth surfaces[END_REF]Descals 1981, Ba ¨rlocher 1992). Conidia of aquatic hyphomycetes released into flowing water may be carried from a few hundred meters to a few kilometers [START_REF] Thomas | A dynamic model of fungal spora in a freshwater stream[END_REF] and can maintain their ability to germinate for several days [START_REF] Iqbal | The trapping of aquatic hyphomycete spores by air bubbles[END_REF]Webster 1973, Sridhar andBa ¨rlocher 1994). However, unlike conidia of many other fungi, those of aquatic hyphomycetes are not designed as resting stages, and their delicate structure suggests that prolonged maintenance of viability is limited (Sridhar and Ba ¨rlocher 1994). Furthermore there is evidence that early establishment on a freshly fallen leaf confers early colonizers a competitive advantage over fungi arriving at a later stage (Ba ¨rlocher andSchweizer 1983, Suberkropp and[START_REF] Chauvet | Regulation of leaf breakdown by fungi in streams: influences of water chemistry[END_REF]. Thus efficient attachment to a suitable fresh substratum is a most critical point in the life cycle of these fungi.

In contrast to most terrestrial fungi, aquatic hyphomycetes show a variety of characteristic conidial shapes, which range from compact to filiform to branched. Tetraradiate shape as the dominant branched type and filiform shape are the most common, with experimental evidence suggesting that more complex shapes result from adaptation to turbulent aquatic environments [START_REF] Webster | Experiments with spores of aquatic hyphomycetes I: sedimentation and impaction on smooth surfaces[END_REF], Webster and Davey 1984, Webster 1987). Accordingly conidia with tetraradiate shape are trapped on surfaces most efficiently, making simultaneous contact with the tips of three of their branches. Filiform conidia are often sigmoid (i.e. twisted in three dimensions), which ensures two contact points, whereas compact forms only have one and consequently should be least efficient at attaching to surfaces, especially in turbulent conditions. Differences in the surface roughness of leaves, both among species and between the upper and lower leaf side, might further influence attachment success. This idea led Ba ¨rlocher (1992) to suggest that some observed difference in community structure of aquatic hyphomycetes on different leaf species in the same stream (Thomas et al 1992[START_REF] Gulis | Are there any substrate preferences in aquatic hyphomycetes?[END_REF]) might be caused partly by varying success among species during the initial conidial settlement and germination phases.

The aim of this study was to determine the variability in attachment success on natural leaf surfaces among the three most common types of conidia (branched/tetraradiate, filiform/sigmoid and compact) belonging to widespread aquatic hyphomycete species. To this end we first compared attachment success on two types of leaves of three aquatic hyphomycete species, each exhibiting one of the three basic conidial shapes. We used black alder (Alnus glutinosa [L.] Gaertn.) and downy oak (Quercus humilis Miller) to test whether leaf surface structure influences conidial attachment by comparing attachment success on the upper (adaxial) and lower (abaxial) sides of leaves. Leaf blades of both species have smooth upper and rougher lower sides, the latter resulting from protruding veins and more or less numerous and extensive tufts. Given the greater importance of tufts on oak leaves, we expected roughness to be greatest on the lower side of oak leaves and lowest on upper leaf surfaces. Thus we hypothesized that (i) differences in surface structure between leaf sides influence conidial attach-ment; (ii) simple compact conidia are less influenced by surface structures than filiform unbranched and tetraradiate conidia, which are more likely to get trapped by tufts; and (iii) filiform and tetraradiate conidia attach more efficiently than conidia with simple compact shape, even on smooth surfaces. In a second experiment we tested with a greater number of fungal species whether tetraradiate conidia are more efficient at attaching to leaves than compact conidia.

MATERIALS AND METHODS

Production of conidia.-All fungal strains were obtained from single conidia isolated from river foam and grown on 2% malt agar (Merck 1.11929). Tetrachaetum elegans Ingold (Te, CERR28-1457), Flagellospora curvula Ingold (Fc, and Heliscus lugdunensis Saccardo & The ´rry (Hl, CERR28-1453) were chosen for the first experiment as representatives of tetraradiate, filiform and compact conidial shapes, respectively (FIG. 1). Five additional species were used in the second experiment. These were Alatospora acuminata Ingold (Aa, CERR28-1464), Articulospora tetracladia (At, CERR28-1458) and Tetracladium marchalianum de Wild. (Tm, CERR28-1454) with tetraradiate conidia, and Goniopila monticola (Dyko) Marvanova ´& Descals (Gm, CERR28-1455) and Tumularia aquatica (Ingold) Descals & Marvanova ´(Ta, CERR28-1461) with compact conidia (FIG. 1).

Sporulation of aquatic hyphomycetes was induced by soaking strips of 7-10 d old colonies on 2% malt agar in microcosms designed for studying fungal leaf decomposition in streams (see Suberkropp 1991 for details). Forty mL of nutrient solution containing per liter 100 mg CaCl 2 ? 2 H 2 O, 10 mg MgSO 4 ? 2 H 2 O, 0.5 g 3-morpholinopropanesulfonic acid (MOPS), 100 mg KNO 3 and 5.5 mg K 2 HPO 4 , with pH adjusted to 7.0 were added to each microcosm [START_REF] Dang | Magnitude and variability of process rates in fungal diversity-litter decomposition relationships[END_REF]. Microcosms and nutrient solutions of cultures were autoclaved before inoculation. Air flow through microcosms was adjusted to 80 mL min 21 during experiments and temperature was maintained at 15 C. Conidia produced after 24-48 h were used in experiments.

Experimental design.-Leaf disks (1 cm diam) were cut from freshly fallen alder and oak leaves with a cork borer, autoclaved, air dried and stored. Although autoclaving and drying of leaves may affect surface structure of leaves, we assumed such changes would be small and that any effects on attachment would vary little across fungal species. Six disks of each leaf species were introduced into each of three replicate microcosms [START_REF] Suberkropp | Relationships between growth and sporulation of aquatic hyphomycetes on decomposing leaf litter[END_REF] and incubated with aeration for 24 h before adding a conidial suspension of a single species. In a first series of experiments about 10 000 conidia for F. curvula and H. lugdunensis or 2000 for the much larger T. elegans were used. Number of conidia in the inoculum was verified by staining and counting the conidia of three additional inocula on membrane filters [START_REF] Gessner | Qualitative and quantitative analyses of aquatic hyphomycetes in streams[END_REF]. The same protocol was followed in the second experiment, except that microcosms were inoculated simultaneously with all seven species and that each of three replicate microcosms received 12 alder leaf disks and ca. 17 000 conidia of each fungal species. [START_REF] Chauvet | Hyphomyce `tes aquatiques du sud-ouest de la France[END_REF]. and counted (see below). Leaf disks were removed carefully from microcosms with tweezers, stained with trypan blue and placed between a slide and cover slip. In the first series of experiments conidial attachment was checked by scanning the entire surface area of both sides of all leaf disks under a Zeiss Axioplan microscope at 1603 to obtain an exhaustive account of all settled conidia. Conidia first were counted on the leaf side facing the cover slip, then the slide was turned upside down and conidia counted on the side facing the slide. In the second experiment to assess success of the two extreme conidial shapes, a total of three lower and three upper sides of the 12 leaf disks per microcosm were scanned.

Data analyses.-Attachment success was assessed as the percentage of conidia attached to each side of all leaf disks from a given microcosm. Because a conidium can settle only on one side of a given disk in a microcosm, conidial attachment events are not statistically independent and analyses with parametric statistical tests are inappropriate (Sridhar et al 2001). However conidial attachment events are independent among replicate microcosms, which were treated as blocks in analyses. The influence of leaf surface structure (i.e. leaf species and side) and fungal species on conidial attachment success was analysed by two-way randomized ANOVA (cf. Ba ¨rlocher 2005) after arcsinesquare root transformation of data; the routine was written in Matlab 6.5 for PC. To maintain independence among blocks, permutations were restricted to within blocks (i.e. microcosms) by shuffling all data (Sridhar et al 2001). After each shuffling (permutation), F-statistics were calculated as in a normal two-way ANOVA. Based on 10 000 permutations significance was inferred from the number of F-values as extreme as, or more extreme than, the initial F-value (i.e. F 0 obtained from the empirically observed data). When the test was significant, differences between pairs were tested by Tukey's HSD test with the same permutation method. In the second experiment, the influence of species on attachment success was analyzed by one-way randomized ANOVA on arcsine-square root transformed data followed by Tukey's HSD test, using similar procedures as in Experiment 1. Finally Spearman's correlation was calculated between effective volume of conidia and attachment success to assess whether conidial size could have influenced attachment success in the second experiment. Effective volume of conidia was approximated by a sphere in the case of tetraradiate conidia and G. monticola, a cone for H. lugdunensis and a double cone for T. aquatica (FIG. 1).

RESULTS

Microscopic observations revealed that all conidia settled on the leaves had germinated. Leaf side had a strong effect on conidial attachment (F 5 68.5, P , 0.0001), with the lower side of oak trapping significantly more conidia of T. elegans and F. curvula than both the upper side of oak and either side of alder leaves (FIG. 2,TABLE I). Microscopic observations showed that when a branch of a tetraradiate conidium or a filiform conidium encountered a hair on the lower side of an oak leaf (FIG. 3) the conidium got entangled and remained trapped and developed one or more germ tubes that often reached the leaf surface. Even the compact conidia of H. lugdunensis were significantly more abundant on the lower side of oak leaves (FIG. 2).

Conidial attachment varied greatly among the three fungal species with a total attachment frequency (all conidia attached to the two leaf species combined) of 70 6 12% (mean 6 1 SD) for the large FIG. 2. Attachment success of three aquatic hyphomycete species on leaves expressed as frequency of inoculated conidia settled on one side of one leaf disk in microcosms (mean 6 1 SE, n 5 18). Alder and oak leaves as well as upper and lower sides of leaves were considered separately. Black, gray and white bars indicate species with compact, filiform and tetraradiate conidia respectively. Leaf species/ side combinations that were significantly different according to randomized Tukey's test are indicated by lowercase letters.

tetraradiate conidia of T. elegans, 16.6 6 5.4% for the filiform conidia of F. curvula and 1.9 6 2.4% for the compact conidia of H. lugdunensis. In contrast to the other species H. lugdunensis never developed appresoria on leaf surfaces. Few conidia of T. elegans remained suspended after 24 h (2.7 6 1.9%), whereas about half (53 6 19%) of the H. lugdunensis conidia remained in suspension. Suspended conidia of F. curvula were not counted because they were not clearly distinguishable from hyphal fragments once they had germinated. Indeed after 24 h conidial suspensions of all species contained a high number of hyphal fragments, although inocula were almost free of hyphae. Inspection of the glass walls of microcosms under a dissecting microscope revealed a substantial number of attached conidia; however, because of the shape of microcosm, it was impossible to obtain reliable counts of these conidia.

Attachment success of the seven fungal species used in Experiment 2 is shown (FIG. 4). Species identity had a highly significant effect (F 5 68.3, P , 0.0001), confirming results from Experiment 1 that large differences in attachment success exist among individual fungal species. There were also significant differences between fungal shapes, with two tetraradiate species exhibiting the highest attachment frequencies (FIG. 4). In accordance with results of Experiment 1 T. elegans conidia were much more successful in attaching to leaves than all other species (38 6 13%) (FIG. 4). The second tetraradiate species (A. acuminata) had significantly lower attachment frequencies of 10.8 6 0.8%, and attachment success of the five other species (tetradiate T. marchalianum 3.4 6 0.7% and A. tetracladia 2.6 6 0.4%, and compact G. monticola 2.7 6 1.1%, H. lugdunensis 1.3 6 1.1% and T. aquatica 1.1 6 0.6%) were similar. As a result multiple comparisons by Tukey's test following randomized ANOVA (TABLE II) differentiated three groups (FIG. 4).

An apparent relationship between size (i.e. effective volume) of conidia and attachment success (FIGS. 1 and 4) was driven strongly by a single species with large conidia and high attachment success (T. elegans) at one extreme and a cluster of smaller species at the other end. As a result effective volume and attachment success were not significantly correlated when assessed as Spearman's rank correlation (r s 5 0.54, P 5 0.22). Further, when this large species was removed from the analysis, the previously apparent relationship disappeared altogether (r s 5

DISCUSSION

To our knowledge this study is the first to estimate the attachment success of aquatic hyphomycete conidia on leaf litter. [START_REF] Webster | Experiments with spores of aquatic hyphomycetes I: sedimentation and impaction on smooth surfaces[END_REF] found that conidial shape significantly influences attachment on collodion-coated objects submerged in flowing water. The present results lend partial support to [START_REF] Webster | Experiments with spores of aquatic hyphomycetes I: sedimentation and impaction on smooth surfaces[END_REF] conclusion that tetraradiate conidia confer a competitive advantage because conidia of two tetraradiate species attached to leaf surface more efficiently than compact forms. However species with tetraradiate conidia exhibited a large range of attachment frequencies, with no statistically detectable difference between the two least efficient tetraradiate and three compact conidia. This suggests that factors other than shape are also important in determining attachment success of aquatic hyphomycetes on leaves.

Higher attachment rates of tetraradiate conidia have been attributed to the greater number of contact points that settling conidia make with the substratum. The rationale is that the tetraradiate shape ensures simultaneous contact at three points and thus results in better adherence on surfaces than the single contact point of compact conidia and two made by sigmoid conidia (Webster and Davey 1984[START_REF] Read | Germination and development of attachment structures by conidia of aquatic Hyphomycetes: light microscope studies[END_REF], Ba ¨rlocher 1992). Why then did conidial attachment success vary markedly among species with conidia of similar shape? [START_REF] Cox | Search theory, random motion and the convergent evolution of pollen and spore morphology in aquatic plants[END_REF] suggested that effective size is important because size is proportional to the probability that a spore hits a target object. This hypothesis is consistent with the high attachment success of T. elegans, the species in our experiments with by far the largest conidia. However A. acuminata, the second most successful species, has conidia of intermediate size only (FIG. 1). Thus, although it cannot be ruled out that conidial size plays a role in determining attachment success, additional factors appear to be influential as well. One additional factor, unrelated to conidial shape or size, might be length of the germ tube that is formed before an appressorium is developed because quick development of appresoria at the end of germ tubes ensures firm attachment of newly settled conidia colonizing leaf surfaces [START_REF] Webster | Experiments with spores of aquatic hyphomycetes I: sedimentation and impaction on smooth surfaces[END_REF]Davey 1984, Read et al 1991;[START_REF] Au | The role of mucilage in the attachment of conidia, germ tubes, and appresoria in the saprobic aquatic hyphomycetes Lemonniera aquatica and Mycocentrospora filiformis[END_REF]. In contrast to G. monticola and the tetraradiate species, which produced short germ tubes before forming appresoria, conidia of T. aquatica usually developed long tubes before an appressorium was formed. This delay in appressorium formation might explain the particularly low attachment frequency of T. aquatica compared to all other species tested.

H. lugdunensis never developed appresoria on leaves in the present study, nor have these structures been observed on either glass surfaces or membrane filters in a previous investigation [START_REF] Read | Germination and development of attachment structures by conidia of aquatic Hyphomycetes: light microscope studies[END_REF]. Lack of an effective holdfast before hyphae penetrate the plant tissue may result in high vulnerability of settled conidia to turbulence, which could wash away conidia that are only loosely attached, consistent with our observation that more than half of the H. lugdunensis conidia added to microcosms remained in suspension after 24 h. The notable absence of appressorium formation in H. lugdunensis might be related to the regular occurrence of this hyphomycete in terrestrial habitats [START_REF] Sridhar | Aquatic hyphomycetes on leaf-litter in and near a stream in Nova Scotia, Canada[END_REF], from where it first was described [START_REF] Saccardo | Conspectus generum fungorum italiae inferiorum[END_REF] and where firm attachment is less critical than in flowing water. Furthermore H. lugdunensis, like T. aquatica, has been reported from submerged wood [START_REF] Shearer | The role of woody debris[END_REF], a much less ephemeral resource than leaves, suggesting that attachment success might play a less critical role in the life cycle of these species compared to other aquatic hyphomycetes. Finally the weaker ability of both H. lugdunensis and T. aquatica to attach to leaf surfaces might be related to the presence of glycogen as dominant carbon storage product [START_REF] Ingold | An illustrated guide to aquatic and waterborne hyphomycetes[END_REF], which has been suggested to reduce germination potential (Read et al 1992).

In addition to conidial shape and other traits of aquatic hyphomycetes, attachment success of conidia was affected significantly by leaf surface structure. Both filiform and tetraradiate conidia were trapped most efficiently by tufts on the lower side of oak leaves (FIG. 3), which functioned like a comb and thus increased settlement rates. We had expected that compact conidia would be less responsive to differences in leaf surface structure. However compact conidia, such as those of H. lugdunensis, also were trapped preferentially by tufts on the lower side of oak leaves (FIG. 3), an observation also made with conidia of G. monticola (data not shown). Microscopic observation suggested that this could be due to the fact that conidia are no longer compact once they have germinated and therefore might get entrapped with their extended germ tubes in a similar way as filiform conidia. Because attachment success was evaluated only 24 h after inoculation of microcosms it is not clear from the present results whether conidia germinated before or after entrapment. However, if they germinated in suspension, it would support [START_REF] Cox | Search theory, random motion and the convergent evolution of pollen and spore morphology in aquatic plants[END_REF] suggestion that alteration of conidial shape by germination might render attachment to leaf surfaces more efficient.

Another critical factor to consider in assessing attachment success of aquatic hyphomycete conidia is thickness of the boundary layer on leaf surfaces. Given the small size even of large conidia (FIG. 1) conidia simply might get trapped in this boundary layer where flow is greatly reduced [START_REF] Statzner | Hydraulic stream ecology-observed patterns and potential applications[END_REF]. Leaf surface structures such as tufts are likely to increase thickness of the boundary layer and thus increase chances of conidia of all sizes and shapes to be trapped, irrespective of a comb effect of tufts.

The weak attachment of conidia in the present experiments is likely to be related to the high turbulence prevailing in stream microcosms, which are aerated from underneath [START_REF] Suberkropp | Relationships between growth and sporulation of aquatic hyphomycetes on decomposing leaf litter[END_REF]). However such turbulent conditions typically are encountered in running water, even though specific hydraulic characteristics may differ between microcosms and the field. Attachment of aquatic hyphomycetes is a critical stage in the colonization of fresh substrata in flowing water. Indeed aquatic hyphomycetes in streams are likely to experience large losses of conidia that never germinate on a suitable substratum. This is because conidia are constantly transported downstream with the unidirectional flow of water and have a tendency to attach to any solid substratum they encounter, such as a leaf or piece of wood, but also to mineral surfaces (Read et al 1992). Additional losses during transport occur through consumption by filter-feeding invertebrates (Ba ¨rlocher [START_REF] Brendelberger | Clearance of aquatic hyphomycete spores by a benthic suspension feeder[END_REF]. In view of the rapid colonization of freshly fallen leaves in streams by aquatic hyphomycetes, it appears that the enormous number of conidia released by these fungi (Ba ¨rlocher 1992) is sufficient to compensate for these losses and inefficiencies in attaching to suitable substrates.

In conclusion the results of this study show that species identity clearly affects attachment success of aquatic hyphomycetes on leaf surfaces. Shape of conidia may partially determine success, whereas the importance of size is not clear, suggesting that other characteristics of conidia are also influential. In addition to conidial traits leaf surface structure plays an important role in determining attachment success, particularly the presence of tufts in which conidia can get entrapped and which are likely to increase thickness of the boundary layer at the leaf-water interface. Given that settling of conidia on, and attachment to, leaf surfaces is a critical step in the life cycle of aquatic hyphomycetes, marked differences in attachment success might have implications for structuring aquatic hyphomycete communities on decomposing leaves in streams. For example T. elegans was highly efficient in the present study at attaching to alder leaves, consistent with the frequent record of this fungus as a dominant species during early stages of leaf colonization in natural streams (e.g. [START_REF] Chamier | Pectinases in leaf degradation by aquatic hyphomycetes I: the field study[END_REF], Ba ¨rlocher 1991a, Gessner et al 1993). However traits of aquatic hyphomycetes, such as efficiency of resource capture, growth rate, competitive ability (Ba ¨rlocher 1991b, [START_REF] Yuen | Interspecific interactions among tropical and subtropical freshwater fungi[END_REF][START_REF] Treton | Competitive interaction between two aquatic hyphomycete species and increase in leaf litter breakdown[END_REF], and resistance to predation [START_REF] Arsuffi | Selective feeding by shredders on leaf-colonizing stream fungi: comparison of macroinvertebrate taxa[END_REF], are likely to be additional determinants that shape aquatic hyphomycete community structure. Considerably more information clearly is needed to elucidate the factors governing establishment of aquatic hyphomycete communities on leaf litter in streams.

  FIG. 1. Conidia of Alatospora acuminata. a. Tetracladium marchalianum. b. Articulospora tetracladia. c. Tetrachaetum elegans. d. Goniopila monticola. e. Heliscus lugdunensis. f. Tumularia aquatica. g. Flagellospora curvula. h. Bar 5 50 mm (a-c, e-h) or 100 mm (d). After[START_REF] Chauvet | Hyphomyce `tes aquatiques du sud-ouest de la France[END_REF].

FIG. 3 .

 3 FIG. 3. View of the lower side of a downy oak leafshowing tuft that might be instrumental in increasing attachment success of aquatic hyphomycete conidia on leaf surfaces. Bar 5 1 mm.

FIG. 4 .

 4 FIG. 4. Attachment success of seven aquatic hyphomycete species on leaves expressed as the frequency of inoculated conidia settled on leaf disks in microcosms (mean 6 1 SE, n 5 3). Tetrachaetum elegans (Te), Alatospora acuminata (Aa), Tetracladium marchalianum (Tm), Goniopila monticola (Gm), Articulospora tetracladia (At), Heliscus lugdunensis (Hl) and Tumularia aquatica (Ta). White bars indicate species with tetraradiate conidia, gray bars species with compact conidia. Species significantly different according to a randomized Tukey's test are indicated by lowercase letters.

TABLE I .

 I Results of two-way randomized ANOVA testing for effects of fungal species and leaf side on attachment success by aquatic hyphomycete conidia

	Factor	SS	df	MS	F	P
	Fungal species	0.77	2 0.39	882.5 ,0.0001
	Leaf side	0.090	3 0.030	68.5 ,0.0001
	Fungal species
	3 leaf side	0.026	6 0.0043	9.8 ,0.0001
	Error	0.089 204 0.00044

TABLE II .

 II Summary of pairwise comparisons (P values) made by randomized Tukey's test of aquatic hyphomycete attachment success on leaves. Alatospora acuminata (Aa),

	Articulospora tetracladia (At), Goniopila monticola (Gm),
	Tetracladium marchalianum (Tm), Heliscus lugdunensis
	(Hl), Tumularia aquatica (Ta) and Tetrachaetum elegans
	(Te)
		Aa	At	Gm	Tm	Hl	Ta
	At	0.005
	Gm	0.004	0.97
	Tm	0.016	0.37	0.36
	Hl	,0.001	0.35	0.38	0.21
	Ta	,0.001	0.29	0.32	0.17	0.90
	Te	,0.0001 ,0.0001 ,0.0001 ,0.0001 ,0.0001 ,0.0001

ACKNOWLEDGMENTS

We thank B. Malmqvist, M. Gardes, M.A.S. Grac ¸a and two anonymous reviewers whose comments led to significant improvements of the manuscript. This study was supported through the RivFunction project financed by the EU Commission (EVK1-CT-2001-00088) and the Swiss State Secretariat for Education and Research (SBF No. 01.0087).