Anaïs Boura
email: anais.boura@sorbonne-université.fr.

Marion Bamford
email: marion.bamford@wits.ac.za

Marc Philippe
email: marc.philippe@univ-lyon1.fr

Promoting a standardized description of fossil tracheidoxyls

Keywords: fossil wood, homoxylous wood, taxonomy, xylology

The palaeoxylology of coniferous woods has progressed considerably since Kräusel's last (incomplete) synthesis in 1949. Nomenclatural practice has slowly purged itself of the diagnostic use of etymology. The use of certain new words or phrases has become essential, while other words have been subject to significant semantic drift or unjustified omission. The interest of secondary characters was highlighted. Ways of describing have also evolved, sometimes in divergent ways. The list of characters (and states) published by the International Association of Wood Anatomists in 2004 represents a fundamental step towards a standardization of practices. However, it does not take into account some of the particularities of palaeoxylology. Here we propose: 1) a plea that etymology should definitely no longer be considered diagnostic; 2) a standardised format for the description of fossil tracheidoxyls; 3) an illustrated glossary of certain terms specific to palaeoxylology.

2 1979; [START_REF] Barefoot | Identification of Modern and Tertiary woods[END_REF][START_REF] García-Esteban | Anatomía e identificación de maderas de coníferas a nivel de especie[END_REF]. Modern authors do not always go back to basics, and for their works rely only on more recent publications. This logically led to a divergence in the semantics of the words used to describe softwoods. All the more as etymology-based hypotheses are still too often used in both the nomenclature and the taxonomy of these woods. In addition, as knowledge progresses, new words have been proposed to avoid long locutions: for example "tracheidoxyl" instead of "detached portion of wood characteristically composed of tracheids with only a minor proportion of other tissues" [START_REF] Creber | Gymnospermous wood from the Kimmeridgian of East Sutherland and from Sandringham Sands of Norfolk[END_REF], or "oculipore" for "half-bordered cross-field pit" [START_REF] Torrey | The comparative anatomy and phylogeny of the Coniferales, Part. 3: Mesozoic and Tertiary coniferous woods[END_REF]. As there has been no recent review of how to describe fossil softwood, these words are rejected by most editors as jargon, and thus are condemned to idiosyncratic uses, despite their undeniable practicality. Finally, more importantly, the completeness of published descriptions for fossil woods differ greatly, with too much variation in attention paid to traits considered secondary.

A formalization seems desirable.

After the IAWA's glossary (1964), the "Inside Wood" project was a huge step forward for hardwoods in standardizing what xylological vocabulary means and how woods are to be described (InsideWood, 2004;[START_REF] Wheeler | InsideWood -a web resource for hardwood anatomy[END_REF]. Similarly, after Slyper's illustrated key (1933) and Phillips' card system (1941), the IAWA list of microscopic features for softwood identification [START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF]) was also such a step. Immo Heinz's thesis (2004), though still unpublished, is also a significant contribution to the study of extant softwoods. These works do not tackle, however, some of the vocabulary that is commonly used for fossil softwoods (e.g. podocarpoid crossfield pit, or mixed type of radial pitting). Later some authors tried to fill some of these gaps (e.g. García [START_REF] García-Esteban | Anatomía e identificación de maderas de coníferas a nivel de especie[END_REF][START_REF] García Esteban | Characterisation of the xylem of 352 conifers[END_REF][START_REF] Merlotti | Método de estudo paleoanatômico aplicado à taxonomia de lenhos gimnospérmicos gondvânicos (Paleozóico Superior)[END_REF][START_REF] Pujana | Podocarpoxylon Gothan reviewed in the light of a new species from the Eocene of Patagonia[END_REF][START_REF] Pujana | Proposals for quantifying two characteristics of tracheid pit arrangement in gymnosperm woods[END_REF].

Our experiences, as authors and as editors, force us to note that a synthesis is necessary regarding the vocabulary and the way of describing fossil softwoods. Here we propose: 1) a plea for the definitive abandonment of any etymologically based implication in the taxonomy of fossil woods; 2) a standardized format for described fossil tracheidoxyls, together with warnings about the tricks played by fossilization that we seem to encounter most often in contemporary palaeoxylological literature; 3) an illustrated glossary of some terms commonly used for softwood palaeoxylology, including three new words to replace longer locutions.

2 Fossil wood nomenclature and etymology Fossil wood anatomy was illustrated as early as 1665 [START_REF] Hooke | Micrographia, or, some physiological descriptions of minute bodies made by magnifying glasses: with observations and inquiries there upon[END_REF], but was first studied in the 1830's [START_REF] Nicol | Observations on the fossil trees of Van Diemen's Land[END_REF][START_REF] Nicol | Observations on the structure of recent and fossil Coniferae[END_REF]. As for softwoods it was not before [START_REF] Eβner | Über des diagnostischen Wert der Anzahl und Höhe der Markstrahlen bei den Koniferen[END_REF], and specially Gothan's thesis (1905), that cross-field pitting was evidenced to be a key taxonomic feature. Subsequently, numerous authors have proposed founding taxonomic syntheses for fossil softwood (e.g. [START_REF] Jeffrey | The comparative anatomy and phylogeny of the conifers. Part II: the Abietineae[END_REF]Kräusel, 1920a andb, 1949;[START_REF] Eckhold | Die Hoftüpfel bei rezenten und fossilen Coniferen[END_REF][START_REF] Seward | Fossil plants[END_REF]. All of these studies have largely used etymology at two levels [START_REF] Philippe | A key to morphogenera used for Mesozoic conifer-like woods[END_REF], ignoring the establishment of nomenclatural rules when they were first promulgated (known as the Vienna rules, 1905).

First in the naming of genera, assigning fossil wood samples to genera not on the basis of diagnoses, but according to which extant genus they thought it was most similar to (see Kräusel, 1917: 306-307 and1918: 129-130). A softwood resembling the wood of a Podocarpus (or of a Podocarpaceae, not always clear) had to be named Podocarpoxylon (see e.g. [START_REF] Tuzson | Monographie der fossilen Pflanzenreste der Balatonseegegend[END_REF][START_REF] Kräusel | Beiträge zur Kenntnis der Hölzer aus der schlesischen Braunkohle[END_REF][START_REF] Greguss | Fossil Gymnosperm Woods in Hungary from the Permian to the Pliocene[END_REF]. It is obvious that this method, largely based on fixist views and idiosyncratic similarity hypotheses, is simplistic. In the minds of these authors, the fossil wood genera not being "natural" ones, escaped the rigor of nomenclatural laws and their names could therefore mnemonically formalise their supposed affinities through etymology. Using mnemonics is not a nomenclatural problem but a hypothesis cannot replace a diagnosis and the etymology cannot be diagnostic ("The purpose of giving a name to a taxonomic group is not to indicate its characters", ICN preamble 1, [START_REF] Turland | International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress[END_REF]. The progression of wood anatomy, by documenting the xylological variability of several extant genera (see e.g. [START_REF] Bailey | The cambium and its derivative tissues. VII: problems in identifying the wood of Mesozoic Coniferae[END_REF][START_REF] Bailey | The cambium and its derivate tissues. IX: structural variability in the Redwood (Sequoia sempervirens), and its significance in the identification of fossil woods[END_REF], evidenced that this approach was not tenable. However, this was not usually admitted before the 1970's, and even much later some authors still explicitly used a taxonomical hypothesis and then etymology to name a fossil wood [START_REF] Greguss | Fossil Gymnosperm Woods in Hungary from the Permian to the Pliocene[END_REF]. Quite often this approach is used still now, more or less conscientiously. The etymology may have played a role in the connection that has sometimes been made between Brachyphyllum Brongniart and Brachyoxylon Hollick & Jeffrey together, although there is no evidence of an exclusive relationship [START_REF] Lemoigne | Caractères histologiques du bois secondaire du Brachyphyllum desnoyersii (Brongniart) de Saporta[END_REF][START_REF] Greppi | Early Cretaceous Brachyoxylon woods from Argentinean Patagonia and comments on the Cheirolepidiaceae distribution[END_REF].

Second is the understanding of the vocabulary used for descriptions. Although conscientious authors have published definitions of the terms they used (e.g. Kräusel, 1920b;[START_REF] Slyper | Bestimmungstabelle für rezente und fossile Coniferenhölzer nach mikroskopischen Merkmalen[END_REF][START_REF] Vogellehner | Zur Anatomie und Phylogenie mesozoischer Gymnospermenhölzer, Beitrag 7: Prodromus zu einer Monographie der Protopinaceae. II: Die protopinoiden Hölzer der Trias[END_REF][START_REF] Vogellehner | Zur Anatomie und Phylogenie mesozoischer Gymnospermenhölzer, Beitrag 7: Prodromus zu einer Monographie der Protopinaceae[END_REF], and more rarely illustrated them, several words have been used with no definition, or with no reference to an original use, i.e. only on the basis of etymology.

One of the foremost examples is the use of the term podocarpoid [START_REF] Philippe | A key to morphogenera used for Mesozoic conifer-like woods[END_REF], which was originally used for a cross-field pit with a narrow linear oblique pore [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF], but subsequently as a large round narrowly bordered cross-field pit [START_REF] Müller-Stoll | Gymnospermen-Hölzer des deutschen Jura. Teil 3: Abietoid (modern) getüpfelte Hölzer[END_REF]. "Podocarpoid" does not mean "like the one encountered in Podocarpus wood" (where cross-field pits are diversified), but rather in fitting with a description (as given first by [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF]. This unjustified use of etymological diagnostics at two levels is characteristic of what was referred to as "etymological naming" [START_REF] Philippe | A key to morphogenera used for Mesozoic conifer-like woods[END_REF]. This has long prevented a homogenisation of nomenclatural approaches, but instead induced a plethoric synonymy, and made syntheses, whether systematic, phylogenetic or biogeographic, extremely difficult.

Moreover, as Latin and Greek are less and less part of common education, etymological implications are nowadays more often misunderstood.

Fossil tracheidoxyl description

A definition is given in the subsequent glossary for terms marked with an asterisk.

Here we propose a template for the description of fossil tracheidoxyls* (Plate I, 1), i.e. softwoods made of tracheids, with only a minor proportion of other cell types. Manoxylic* woods (Plate I, 2) consist of a large proportion of axial parenchyma and are not concerned here, tracheidoxyls being typically pycnoxylic* (Plate I, 1). Homoxylous angiosperms might have a wood superficially similar to softwoods, but apart from some rare exceptions [START_REF] Philippe | Ecpagloxylon mathiesenii gen. et sp. nov., a Jurassic wood from Greenland with several primitive angiosperm features[END_REF], are usually easy to distinguish.

Referring to a template has the advantage of making the absence of a character more explicit.

Thus the descriptions can become more concise, avoiding statements like "axial parenchyma not observed". It also makes it easier to access information as its position in the text is standardised.

Xylological descriptions of softwoods are already standardised to a certain extent, since the majority of authors describe the woods in a sequential way, starting with the cross-section, then the tangential and radial axial sections. This way, however, implies repetition, and the dispersion of characters specific to each cell type. Here we propose a template where, after some general lay out features, each wood cell type is described independently by integrating observations made in each of the section plans. Heteroxylous woods are usually described in this way today.

The description is limited to microscopic features. Macroscopic features are also of interest, in particular axis diameter (measured or estimated from ring curvature), as several wood features are a function of radius: ray height; tracheid width and hence pit seriation; resin canal density; etc.

Continuously variable parameters, such as the diameter of pits in µm, are of undeniable interest for the diagnosis of today's woods [START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF]. Their interest for fossil woods is more debatable. The values they take are indeed strongly influenced by the type of fossilization (Röβler et al., 2021). During charcoalification the diameter of the pits can decrease by more than 30%, while the sideritization can increase it by almost 20% [START_REF] Philippe | Bois fossiles du Jurassique de Franche-Comté (nord-est de la France) : systématique et biogéographie[END_REF]. Most fossilization processes induce allometric transformations. Quantification is desirable. All too often, however, quantification is practiced as an end in itself, which can border on scientism, and does not encourage perspective taking Fossilization often plays tricks that have often deceived palaeoxylologists, in particular steinkerne preservation, pore broadening and false spirals. By steinkerne preservation, which is very common, especially in silicified woods, the areolate pit inner chamber is maintained, more or less completely, while its real rim is indistinct [START_REF] Bamford | Long overdue extinction of the Protopinaceae[END_REF]. This type of preservation was known to [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF], who wrote of "Steinkerne" preservation (literally "stone kernel"). When this occurs, araucarian* pitting displays small rounded and spaced casts instead of larger contiguous and deformed pits and can be confused with abietinean* pitting. Usually two criteria can be used to avoid misidentification of a uniseriate araucarian* radial pitting preserved as Steinkerne as opposed to abietinean* radial pitting: first, the areole is usually at least faintly marked, either by a paler crown around the pore, or by a darker line at the rim of the areolate pit chamber; secondly, in araucarian* radial pitting the spacing between pit pores is usually constant, which is rare in abietinean* pitting [START_REF] Bamford | Long overdue extinction of the Protopinaceae[END_REF]. Steinkerne preservation should be suspected anytime pits look relatively small on the radial wall. [START_REF] Thinon | Description codifiée des caractères anatomiques des bois carbonisés des conifères et des Gingkoales[END_REF] and [START_REF] Gerards | Comparison of cross-field pitting in fresh, dried and charcoalified softwoods[END_REF] have shown that by charcoalification pit pores often significantly widen. This has a particular impact on the characterization of cross-field pits, for which the ratio between pore and pit outline is much used. It is possible that other types of fossilization allometrically alter the microscopic characters of the woods. Indentures usually shrink during the taphonomic process [START_REF] Thinon | Description codifiée des caractères anatomiques des bois carbonisés des conifères et des Gingkoales[END_REF], while microbial attack deeply modifies most cell walls (Anagnost, 1998;Schweingruber and Börner, 2018).

There are multiple types of structures that are known to have been confused with helical thickenings [START_REF] Philippe | A palaeobiogeographical scenario for the Taxaceae based on a revised fossil wood record and embolism resistance[END_REF]: tracheid wall checking by compression wood; oblique furrows at the bottom of which a pit pore is located, also by compression wood; zoned patterns caused by discontinuous crystal growth; crystal cleavage planes by polyblastic mineralization [START_REF] Buurman | Mineralization of fossil wood[END_REF]; tunnelling by bacteria or fungi; shrinkage cracks induced by wood diagenesis; microbial erosion of the tracheid wall that emphasizes the S2 microfibrillar patterns.

The saproxylic process can begin even before the wood is entrained in the taphonomic process, when it is still inside a living tree. Saproxylism is of enormous ecological importance, and it leaves visible traces in the majority of fossil woods. Traces of arthropods or bivalves have been mentioned or studied for a long time, but it is only recently that the authors have begun to describe the effects of bacterial and fungal attacks (e.g. [START_REF] Stubblefield | Wood decay in silicified gymnosperms from Antarctica[END_REF][START_REF] Scaramuzza Dos Santos | Fungus-plant interactions in Aptian Tropical Equatorial Hot arid belt: White rot in araucarian wood from the Crato fossil Lagerstätte (Araripe Basin, Brazil)[END_REF]. As these attacks often modify the appearance of the wood, it is important to describe them before coming to the description of the wood cells. Such features are: occurrence of pocket rots; occurrence and type of hyphae (septate or not, branched or not); occurrence and type of propagules or spores; presence of dark substance; loss or degradation of a more or less important parts of cell walls (middle lamella, primary wall, secondary wall); bacterial slime within tracheid lumen.

Below are lists of the character states for each of the features that should be looked for to assist with capturing all the important features for describing and identifying fossil softwood.

The numbers between brackets refer to the IAWA's softwood features coding [START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF]

Glossary

Only those terms commonly used for tracheidoxyls but which are not illustrated in IAWA's list [START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF] are treated. The reader is warned that the definitions given here are based on the first time the term was used, and that subsequent semantic shifts have occasionally occurred, which are not taken into account. For each entry the author who first used the term for fossil wood is quoted. Some old literature might have been overlooked, however the term in the indicated reference is used according to its "original" meaning. An additional reference indicates that the definition has been further clarified. For some terms it was not possible to clearly identify a first use.

Remark: [START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF] first used "araucarioid" to describe both a type of cross-field and a type of a pitting on the radial wall of tracheids. Eckhold, who formalised Kräusel's ideas on Protopinaceae in his thesis (1923), used the same suffix "-oid" for intertracheary radial wall pitting. In order to avoid confusion it is clearer to reserve the use of this "-oid" suffix for the elements of the cross-fields, and to use suffix "-ean" to describe the way intertracheary pits are distributed on the radial wall.

Abietinean [START_REF] Eckhold | Die Hoftüpfel bei rezenten und fossilen Coniferen[END_REF][START_REF] Philippe | Bois fossiles du Jurassique de Franche-Comté (nord-est de la France) : systématique et biogéographie[END_REF] (Plate III, 1): a pit in the radial wall of a tracheid with its "height/width" ratio equal to or higher than 1, distant from neighbouring pits. By extension, a type of pitting on the radial walls of tracheids where more than 95 % of the pits are of the abietinean type. See e.g. fossil-genus Podocarpoxylon Gothan in Gagel.

Abietineentüpfelung [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF]: pitting of the cross walls of ray cells by contiguous rounded pits (Plate I, 7; Plate V, 2 & 3). See e.g. fossil-genus Protocedroxylon Gothan. While Gothan proposed the term in 1905, he gave a definition in 1906 only (second footnote on page 2). It reads as "the strong bumpy thickening of the medullary ray cell walls (horizontal and vertical)" (our translation). As far as by extant woods the horizontal (i.e. radial) ray cell walls can be strongly nodular without the transverse walls being pitted, it seemed sensible to partially limit Gothan's definition [START_REF] Philippe | A key to morphogenera used for Mesozoic conifer-like woods[END_REF].

Araucarian [START_REF] Eckhold | Die Hoftüpfel bei rezenten und fossilen Coniferen[END_REF][START_REF] Philippe | Bois fossiles du Jurassique de Franche-Comté (nord-est de la France) : systématique et biogéographie[END_REF] (Plate III, 2): a pit in the radial wall of a tracheid with its "height/width" ratio comprised between 1 and 0.6, contiguous with at least one neighbouring pit. By extension a type of pitting on the radial walls of tracheids where more than 95 % of the pits are of the araucarian type. See e.g. Agathoxylon Hartig.

Araucarioid [START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF]: a cross-field with several contiguous and alternate oculipores. See e.g. Agathoxylon Hartig.

Bars of Sanio [START_REF] Müller | Über die Balken in den Holzelementen der Coniferen[END_REF]: also known as trabeculae, these are cylindrical bars crossing the lumen of the tracheids from one tangential wall to another. When present it generally appears in series and always at the same height. Its origin is not completely defined but is probably exogenous, and thus it cannot be considered as having analytical value. They were first described by [START_REF] Sanio | Anatomie der gemeinen Kiefer (Pinus sylvestris)[END_REF], and for a time confused with Sanio's rims [START_REF] Larson | The vascular cambium: development and structure[END_REF].

Such are common e.g. by Taxodioxylon Hartig.

Brachyoxylean (new term) (Plate III, 3 & 4): also called mixed-type or intermediate-type or transitional type (Übergangstypus, Eckhold, 1923), this is a type of pitting on the radial wall of tracheids where less than 90% of the pits are araucarian or abietinean or xenoxylean. See e.g. Brachyoxylon Hollick & Jeffrey.

Circopore [START_REF] Marguerier | Anatomie comparée et systématique des Podocarpus malgaches[END_REF] (Plate V,6 & 8): this type of cross-field oopore was first described by Kräusel (1949: 156) as circular, or at most radially oval, but never obliquely elliptic. Later [START_REF] Vogellehner | Zur Anatomie und Phylogenie mesozoischer Gymnospermenhölzer, Beitrag 7: Prodromus zu einer Monographie der Protopinaceae[END_REF] defined circoporoid as a type of cross-field with "one, rarely two, large round to broadly elliptic but never inclined oopores occupying the whole field". See e.g. Circoporoxylon Kräusel (recently reviewed in [START_REF] Xia | 1-6-Transverse section (Trs); 1-Tracheidoxyl (pycnoxylic wood), Xenoxylon phyllocladoides Gothan, Gothan 117, Swedish Museum of Natural History; 2-Manoxylic wood, Medullosa sp., Collection Roche (n°1166), MNHN, Paris ; 3-Type D & E of growth rings, Cedroxylon cedroides Gothan, S1944, Swedish Museum of Natural History; 4-Type D & E of growth rings, Indeterminate conifer, VI41, paleontological collections of the Université de Poitiers; 5-False rings, Callitrixylon gallicum Privé et Boureau, 5190, Sorbonne Université ; 6-Double rings, indeterminate conifer mentioned in Pons & Henri (1992); 7-Tangential longitudinal section (Tls), abietineentupfelung and occurrence of intercellular spaces between ray cells, Protopiceoxylon exstinctum Gothan, S[END_REF].

Cupressoid [START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF][START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF]): an oculipore with an oblique pore (or aperture), included within the limit of the pit border, usually broadly bordered. See e.g.

Cupressinoxylon Göppert (nom.cons., see [START_REF] Bamford | Proposal to conserve the name Cupressinoxylon Göppert (Fossil, Gymnospermae, Coniferales) against Retinodendron Zenker (Fossil, Gymnospermae, Coniferales), with a conserved type[END_REF].

Dacrydioid [START_REF] Greguss | Fossil Gymnosperm Woods in Hungary from the Permian to the Pliocene[END_REF] (Plate V, 6 & 9): a relatively small (occupying less than half the whole field area) round circopore See e.g. Dacrydioxylon P. Greguss ex A. Selmeier.

False ring [START_REF] Christison | On the difficulty of ascertaining the age of certain species of trees in Uruguay, from the number of rings[END_REF] (Plate I,5 & 6): also known as "false latewood band", "double growth ring", "intra-annual growth ring" or "intra annual density fluctuation (IADF)"; the term of false-ring was used for both symmetric rings and asymmetric but laterally discontinuous rings. Symmetric false rings are marked by a more or less gradual decrease in the tracheid diameter and increase in the wall thickness (like in true latewood), after which there is a smooth transition back to larger lumens and thinner tracheid cellular walls.

Glyptostroboid [START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF] Juniperustüpfelung [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF] (Plate V, 2 & 3): pitting of the cross walls of ray cells by scalariform pits. See e.g. Juniperoxylon C.Houlbert Manoxylic (Plate I, 2) Seward 1917-The terms "manoxylic" and "pycnoxylic" were originally introduced by Seward (1917) to differentiate the looser-textured and parenchymatous extant cycadean wood from the more compact extant coniferous wood. Since a continuum of tracheid diameter, tracheid/parenchyma cell proportion and ray frequency could be noticed in numerous species, Galtier (1992) introduced quantitative features to complete Seward's definition. According to Galtier (1992), manoxylic wood show 1) large diameter tracheids (up to 150 µm), 2) large rays, both broad (more than 5 cells width) and tall (up to 200 cells high).

Oculipore [START_REF] Torrey | The comparative anatomy and phylogeny of the Coniferales, Part. 3: Mesozoic and Tertiary coniferous woods[END_REF]: an areolate cross-field half-pit (semi-areolate pit -half-bordered pit), the border can be narrower than or broader than the pore ("resembles the conventional figure of an eye", [START_REF] Torrey | The comparative anatomy and phylogeny of the Coniferales, Part. 3: Mesozoic and Tertiary coniferous woods[END_REF]. See e.g. Taxodioxylon Hartig.

Oopore [START_REF] Kraus | Mikroskopische Untersuchungen über der Bau lebenden und vorweltlicher Nadelholzer[END_REF]: an unbordered (or simple) cross-field pit. Most authors admit that oopores can be occasionally narrowly bordered. See e.g. Xenoxylon W. Gothan.

Phyllocladoid [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF][START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF] (Plate V, 6 & 7): an oblique elongated oopore, usually with pointed tips. See e.g. Phyllocladoxylon W.Gothan.

Pinoid (Thinon1994) (Plate V, 6): a cross-field with pits of various sizes and shapes, areolated or not. See e.g. Pinuxylon W.Gothan.

Podocarpoid [START_REF] Gothan | Zur Anatomie lebender und fossiler Gymnospermen-Hölzer[END_REF] (Plate V, 6): an oculipore with an oblique to almost vertical slitlike to narrowly linear pore. See e.g. Protopodocarpoxylon W.Eckhold (nom.cons., see. [START_REF] Bamford | Proposal to conserve the name Cupressinoxylon Göppert (Fossil, Gymnospermae, Coniferales) against Retinodendron Zenker (Fossil, Gymnospermae, Coniferales), with a conserved type[END_REF]. Pycnoxylic (Plate I, 1) Seward 1917 -see manoxylic-Pycnoxylic wood designate dense and compact wood composed mainly of tracheids (instead of parenchyma) as in conifers.

According to Galtier (1992), pycnoxylic woods show a combination of 1) small diameter of tracheids (less than 50 µm), 2) small size of rays, both uniseriate and short.

Rim of Sanio [START_REF] Groom | The structure of the wood of East Indian species of Pinus[END_REF] (Plate IV, 1 & 2): Rims of Sanio (or Sanio's rim or crassulae) are thickenings in the primary wall and the middle lamella. They are associated with the bordered pits and are best observed on the radial wall of the axial tracheids. They were first described by [START_REF] Sanio | Anatomie der gemeinen Kiefer (Pinus sylvestris)[END_REF] and often confused with Sanio's bars (Larson, 2012) (figure). See e.g. some Taxodioxylon Hartig.

Septa (e.g. [START_REF] Thomson | On the comparative anatomy and affinities of the Araucarineae[END_REF] (Plate IV, 8): The term has been used to refer to two different things: occasional perpendicular partitioning of the tracheids, including primary and secondary walls; and structures of unknown nature, not belonging to the normal cell wall.

These are not to be confused with trabeculae (figure). The first type of structure was described by [START_REF] Thomson | On the comparative anatomy and affinities of the Araucarineae[END_REF] and is to be found e.g. in Dadoxylon arduennense [START_REF] Lemoigne | Nouvelle espèce de Dadoxylon à trachéides septées provenant du Wealdien de Féron-Glageon (Nord)[END_REF], while the second is especially common in Xenoxylon [START_REF] Arnold | Silicified plant remains from the Mesozoic and Tertiary of western North America. II. Some fossil woods from northern Alaska[END_REF][START_REF] Medlyn | Conifer wood from the Upper Jurassic of Utah part I: Xenoxylon morrisonense sp[END_REF][START_REF] Philippe | Systematics of a palaeoecologically significant boreal Mesozoic fossil wood genus, Xenoxylon Gothan[END_REF]. Taxodioid [START_REF] Kräusel | Die Bedeutung der Anatomie lebender und fossiler Hölzer für die Phylogenie der Koniferen[END_REF][START_REF] Richter | IAWA list of microscopic features for softwood identifications[END_REF]) (Plate V, 6): a narrowly bordered oculipore, with a broad elliptic included pore. See e.g. Taxodioxylon Hartig.

Tracheidoxyl [START_REF] Creber | Gymnospermous wood from the Kimmeridgian of East Sutherland and from Sandringham Sands of Norfolk[END_REF] (Plate I, 1): a detached portion of wood characteristically composed of tracheids with only a minor proportion of other tissues (figure).

Xenoxylean [START_REF] Philippe | Systematics of a palaeoecologically significant boreal Mesozoic fossil wood genus, Xenoxylon Gothan[END_REF] (Plate III, 6): a type of pit in the radial wall of a tracheid with its "height/width" ratio lower than 0.6. By extension, a type of pitting on the radial walls of tracheids where more than 95 % of the pits are of the xenoxylean type (figure).

Characteristic of Xenoxylon W.Gothan.

Conclusion

New elements are presented in the hope of facilitating a more standardized description of tracheidoxyls. Only this will allow truly effective comparisons to be made. Coupled with a nomenclatural framework finally freed from the many oddities accumulated by a practice not very attentive to the rules of the ICN, more formalized descriptions will allow one to use all the enormous potential of fossil softwoods for paleoecology or paleogeography.

The next challenge remains the production of a taxonomic key that is not limited to the Mesozoic like that of [START_REF] Philippe | A key to morphogenera used for Mesozoic conifer-like woods[END_REF] but takes into account all the diversity of the tissue that, at least in terms of biomass, has dominated continental ecosystems for nearly 300 million years.

  . Intertracheary pitting types (abietinean* (Plate III, 1), araucarian* (Plate III, 2), brachyoxylean* (Plate III,3 & 4), shimakurean* (Plate III, 5), xenoxylean* (Plate III, 6)) are not included in this template insofar as the determination of this type is already partly interpretative, and therefore belongs to a discussion. General cell layout tracheidoxyl*; ring curvature; occurrence of true (complete and asymmetrical) growth-rings(present [40], indistinct or absent[41], present but narrow -for respectively, the "A", "B" and "C" types, the "O" type, and the "D" and "E" (Plate I,3 & 4) types according to the Creber and Chaloner's nomenclature(1984); type of transition from the early-to the late-wood when developed[42][43]; proportion of early-wood to late-wood; occurrence of false rings* (Plate I, 5 & 6), either symmetrical or incomplete; occurrence of intercellular spaces [53]; relative position of the tracheid in relation to its tangential neighbours (opposite or alternate); other features (e.g. late wood much developed, circular shape of tracheid cross-section, spiral cracks in axial tracheid walls, wavy rings, branch traces, traumatic areas, fleck marks, etc.). Rays homogenous (including only parenchyma cells) or heterogeneous (occurrence beside normal uniseriate rays of fusiform rays and/or of rays with a radial resin canal); rays homocellular (including one type of cell only) or heterocellular (rays including several cell types and/or cell size as in the case of broader marginal cells or of ray tracheid) (Plate II, 1 & 2); for each type of ray seriation (uniseriate [107], locally biseriate [108], multiseriate (Plate II, 3) and ray height in number of cells (minimum, average, maximum) [102-106] and/or in µm [101]; occurrence of intercellular spaces between ray cells (Plate I, 7). Axial tracheids Cross-section shape (circular (Plate II, 4) or polygonal (Plate II, 5); relative tracheid wall thickness (relative to the lumen, in early and late wood [54-55], tracheid size (diameter and length [49-52], if measurable); variability of tracheid diameters along radial rows. Shape (round, elliptic, obround, xenoxylean*(Plate III, 6), scalariform (Plate III, 7)), size and disposition (contiguous or distant) of intertracheary areolated pits on the radial wall of tracheids; their seriation (uni-[44], bi-or multi-seriate [45] and their relative position in the earlywood when bi-(multi-)seriate (alternate [47], opposite [46], in distinct bands (Plate III, 8) or clustered (Plate III, 9); variation of radial pitting through the growth-ring; occurrence of Sanio's rims* (Plate IV, 1 & 2); torus [56] and margo characteristics (round, scalloped [57], extensions [58]); radial pits peculiar features (such as notched borders [59], other). Pits on the tangential walls of tracheids (Plate IV, 3), their size, their disposition and their distribution in the ring. Occurrence [61] and characteristics (localization within the ring [62-64], single [65] or grouped [66], more or less spaced [67-68], angle from the horizontal) of tertiary thickenings (spirals, callitroid [71], others) or other cell wall ornamentation (warty layers [60]). Other features like resiniferous [48] or mineral contents (Plate IV, 4); occurrence of storeyed or crooked (club-shaped) tips (Plate IV, 5), tyloses (Plate IV, 6 & 7), septae (Plate IV, 8), Bars of Sanio* (Plate IV, 9), etc. Axial parenchyma (epithelial and subsidiary cells of intercellular canals excluded). Occurrence [72]; distribution through the ring (diffuse [73], tangentially zonate[74], marginal[75]); association with rays; inflated or not; transverse walls, thin or thick, nodular [77-78] or smooth [76]; pitting of the axial parenchyma, on normal walls and in cross-fields; including crystals [118, 123] or not, type of crystals (prismatic [119], druses [120], other forms [121]); resiniferous or not. Ray parenchyma: shape in cross-section; cell length; angle of transverse walls; thickness of walls; occurrence of pits (unpitted [85], distinctly pitted [86], abietineentüpfelung* (Plate I, 7; Plate V, 1), juniperustüpfelung*(Plate V, 2 & 3) in ray cell end walls; occurrence of pits (unpitted [87], distinctly pitted [88]) in horizontal walls; occurrence of indentures [89]; type(s) of crossfield [90-95] (Plate V, 6) semi-areolated (cupressoid*, podocarpoid*, taxodioid*) or unbordered (oopore*, circopore* (Plate V, 8), phyllocladoid*(Plate V, 7) oopore) pits in the early wood cross-fields; number (minimum, average, maximum) [96-100] and disposition (spaced, in lines, grouped, contiguous, araucarioid*, circoporoid*, dacrydioid* (Plate V, 8), glyptostroboid*, pinoid*) of crossfield pits in the early wood; variation of crossfield pitting through the growth ring; presence [118, 122] and type of crystals (prismatic [119], druses [120], other forms [121]). Ray tracheids: occurrence [79-80]; size; wall thickness, characteristic (smooth [81], dentate [82], reticulate [83]) and pitting (unpitted or distinctly pitted, pit borders angular or with dentate thickenings [84]); tertiary thickenings (present [69-70] or absent). Axial and/or radial resin-canals: occurrence (normal [109-110] or traumatic [111] or absent), grouping and position within the ring; size (tangential and radial diameter delimited by epithelial cells diameter [112-115]); traumatic or not, their distribution within the ring; feature of the resin-canal lining epithelial cells (thick [116] or thin-walled [117]); presence [124] and type of crystals (prismatic [119], druses [120], other forms [121]). Idioblasts (Plate V, 4 & 5): occurrence; size; distribution.

  (Plate V, 6): a cross field with numerous isodiametric small rounded oopores. See e.g. Glyptostroboxylon Conwentz. Idioblastic cell / Idioblast (not sensu Nägeli, 1884) (Plate V, 4 & 5): Idioblasts are cells conspicuously different from surrounding cells. They are isolated and usually swollen. They can contain tannins, oils, crystals or other material. They are uncommon in tracheidoxyls. See e.g. Ecpagloxylon Philippe, Cuny & Bashforth, Eristophyton M.D. Zalesky.

  Shimakurean (new term = japonicum-type in Philippe et al., 2014) (Plate III, 5): a type of pitting on the radial walls of tracheids were pits are contiguous, biseriate, opposite, squareshaped. See e.g. Shimakuroxylon Philippe, Boura, Oh & Pons.

Acknowledgments

Most of the ideas developed here originate from conversations with many colleagues, editors and authors. Even if these categories are largely overlapping, there are still a lot of people to whom we apologize for mentioning here only four names: Denise Pons, Patrick Herendeen; Elisabeth Wheeler and Gea Zijlstra. Anne Laure Decombeix and Brigitte Meyer-Berthaud are warmly thanked for the edition of this special volume dedicated to someone we particularly appreciate. The advice of two anonymous reviewers is much appreciated. Literature Anagnost, S.E., 1998. Light microscopy diagnosis of wood decay. IAWA Journal 19, 141-