STRUCTURE A~D RELATIONSHIPS OF SOME MIDDLE DEVONIAN

FROM WESTERN NEW YORK 1

Chester A. Arnold

THE remains described here are some addi- (1938) ; Iieimannia aldenense Arnold (1935) ; Schi­ tions to a very interesting flora present in two hori- zopodium M ummii Read (1938) ; I ridopteris erien­ zons in the Hamilton group of western New York. sis Arnold gen. et sp. nov.; Xenocladia medullosina The uppermost of the plant-yielding beds is the Arnold gen. et sp. nov. Tully pyrite, which is so named because it was for- Of the genera in the above list, only two, Schizo­ merly considered equivalent to the Tully limestone podium and Aneurophyton, were originally describ­ which prominently marks the base of the Upper De- ed from elsewhere. Reimannia was first described vonian in the central part of the state. The limestone from the Ludlowville shale at Alden, but has since itself does not extend into western New York, and been recognized in the New Albany shale in Ken­ recent stratigraphical work indicates that the pyrite tucky (Read and Campbell, 1939). The remaining bed instead of being a westward extension of the genera, Arachnoxylon, Iridopteris, and Xenocladia, limestone horizon, as was once believed, belongs to are known only from western New York. the upper part of the Middle Devonian (Hamilton). 1\11'. Irving G. Reimann, of the Buffalo Museum Although the name "Tully pyrite" is retained as a of Science, is mainly responsible for the collections convenient designation, age identity with the Tully of plant-bearing nodules from the Ludlowville shale limestone is no longer implied. The other plant- at Spring Creek, and Mr. Max J. Kopf, of Lancas­ bearing horizon is lower and is contained within the tel', New York, supplied most of the material from Ledyard member of the Ludlowville shale. It is sepa- the Tully pyrite. rated from the Tully pyrite by the Moscow shale Iridopteris eriensis gen. et sp. nov. (fig. 1,5).­ and the Tichenor limestone which together have a The name Iridopteris eriensis is proposed for a well thickness of about fifty feet. preserved axis from the Tully pyrite. The structure The plants from both horizons are pyritized and measures about 4 X 5 mm. in cross section, and the show cell structure, but microscopic examination is shape of the xylem strand is distinctive. The strand possible only with reflected light. In the Tully py- is a solid mass of tissue of five "arms" centrally rite the plants occur as wood and stem fragments united but so arranged that four are in opposing scattered sparingly among the invertebrate fossils pairs, with the fifth one occupying a median posi­ that make up the bulk of the lenticular pyritic tion to one side (fig. 1). The configuration reminds masses. Although preservation of the tissues is often one of the fleur de lis, which in turn suggests the good, the preserved parts are small and consist most- name I ridopteris. No marked changes have been ob­ ly of slivers resulting from the disintegration of served in the xylem at different levels, although the larger pieces of wood. All the plant remains de- structure has not been followed for a length of more scribed in the present paper were collected in than two centimeters. It is possible that the entire Erie County where they are abundantly distributed section comes within the limits of a single internode. throughout the Tully pyrite. Read (1938) also re- N ear the extremity of each"arm" are one or two ports their occurrence at the same level in Ontario small parenchyma filled spaces (fig. 5), the so­ County. In the Ludlowville shale in Erie County the called "peripheral loops." These evidently mark the plants occur in small marcasite nodules embedded in position of the protoxylem and suggest relationship the gray shale, and the most prolific locality is in the with certain Paleozoic ferns as the Cladoxylaceae bed of Spring Creek just east of the village of or the Zygopteridaceae. Passing off laterally from Alden. These nodules contain a variety of inverte- the extremities of these "arms" are small traces (fig. brate remains as well as plants. 5 at A) which apparently supply rachial pinnules Although Dawson (1862) included brief descrip- borne directly upon the main axis between the larger tions of structurally preserved plants from western divisions. These have not been followed beyond the New York in his inclusive studies of the Devonian point of departure from the main xylem strand. Ly­ plants of eastern North America, no systematic at- ing directly opposite the ends of the xylem "arms" tempts have been made to resume the study of them are rather large bundles which apparently constitute until recently. In 1935 the present author described the traces of the pinnae or whatever type of struc­ two new species from Erie County, and in 1938 Read ture sprang from the axis. Five of these lying oppo­ described additional material from the Tully pyrite site the xylem "arms" and in various stages of de­ at Canandaigua Lake in Ontario County. Altogether parture may be observed in a single well preserved six structurally preserved forms are now known cross section. Three traces are indicated in figure 5 from the Hamilton group. These may be listed as at B, C, and D. (The remaining two are shown in follows: Anellrophyton Hallii (Dawson) Arnold outline but are not lettered.) These larger traces comb. nov.; Arachmoxulon. Kopji (Arnold) Read appear to be given off in spiral sequence. Some of 1 Received for publication October 31, 1939. them contain an internal parenchymatous area which [The Journal for Junuary (97: 1-56) was issued February 9,1940.] A:\IERICAN JOURNAl. OF BOTANY, VOl•• 97, No.9, FEBRUARY, 1940. 57 58 AMERICAN JOURNAL OF BOTANY [Vol. 27,

Fig. 1-4.-Fig. 1. Iridopteris eriensis Arnold gen. et sp. nov; Transverse section of axis. Tully pyrite. XI3.-Fig. 9. Aneurophqton. Hallii (Dawson) Arnold comb. nov. Transverse section showing 3-angled primary xylem surrounded by secondary xylem. Ludlowville shale. X6%.-Fig. 3. A. Hallii (Dawson) Arnold comb. novrTransverse section of stem showing sclerenchyma strands in cortex. X6%.-Fig. 4. Xenoeladia medullosiua Arnold gen. et sp. nov. Portion of polystelic axis showing two complete steles and portions of three others. Tully pyrite. xeo.

indicates mesarch structure. The small traces do not terpret the five lobed structure of Iridopieris as such seem to be arranged in the same spiral sequence as an organ. The apparent spiral sequence of the traces the larger ones. in Iridopteris, combined with the symmetry of the The clear zone completely surrounding the xylem axis, indicates an upright structure which was prob­ appears to mark the extent of the phloem (fig. 1), ably the main stem of the plant, and the simplicity of and the large "bays" between the xylem points prob­ the trace structure suggests small pinnae or simple ably contained considerable parenchyma in addition leaves. The traces may have stopped short of the to phloem. Outside the supposed phloem zone there leaves as in Asteroeqlon, but this is mere supposi­ is a somewhat interrupted layer of cells with dark tion without supporting evidence. contents which may be the pericycle, The cortex con­ The two most important anatomical features pres­ sists entirely of parenchyma within which the traces ent in I ridopteris are (1) the parenchymatous areas are imbedded. present near the extremities of the xylem "arms" Aside from the odd number of xylem lobes of the and (2) and the well developed leaf traces arising strand of Iridopteris the structure is comparable in apparently in spiral sequence. The first is indica­ many respects to the zygopterid and cladoxylaceous tive of affinity with certain Paleozoic fern-like forms phyllophore, In the Zygopteridaceae, however, the belonging to the Cladoxylaceae and the Zygopterida­ pinnae are arranged in two or four rows on the phyl­ ceae. Aside from these, the only other group of Pa­ lophores, and consequently it would be difficult to in- leozoic plants to which Iridopteris might be assigned Feb., 19401 ARNOLD-MIDDLE DEVONIAN PLANTS 59

is the Psilophytales, but both of the features men­ Occurring as it does in the Middle Devonian, I ri­ tioned above render reference to this group undesir­ dopteris antedates by a considerable time interval able. Another fact to consider is the pronounced bi­ Asteropteris, which occurs in the Portage and which lateral symmetry of the axis which also points to is commonly cited as the oldest known fern. affinities with the ferns. Although bilateral sym­ The problem of fitting a plant of the I ridopteris metry is exhibited by Asteroxylon elberfeldense, it type into any established scheme of classification is is not as pronounced as in our form. heightened by lack of information concerning foliage and fructifications. Even though the anatomical evi­ 6 dence may be entirely in favor of the establishment of a new group above generic rank, many investiga­ tors oppose doing so on such evidence alone. How­ ever, there are occasions when such procedure can hardly be avoided, and the dangers confronted are due not so much to the fact that anatomical criteria are employed but rather to the usual inadequacy of any single set of factors in determining relation­ ships. Because of the fragmentary condition of most plant fossils, classification is highly artificial. The only way to classify Iridopteris is to weigh the anatomical evidence carefully and then to decide whether the balance favors reference to any estab­ lished group. Obviously but unfortunately, such evi­ dence as is lacking (in this case the foliage and fructifications) must be left out of consideration. In Iridopteris the tips of the xylem "arms" show the parenchymatous areas, or "peripheral loops," near the tips in a similar position to those in Arach­ llox,1Jlon and Reimannia. A rachnoeqlon, however, lacks leaf traces (or at least they have not been ob­ served), and the xylem strand itself is decidedly psilophytic. Read (1938) has referred A rachnoxylon Fig. 5-7.-Fig. 5. Iridopteris eriensis Arnold gen. et sp. to the Psilophytales, but he also considers it a proto­ nov. Camera lucida outline sketch of transverse section type of the Zygopteridaccae. The present author is of axis showing shape of the fluted xylem strand and posi­ in complete agreement with this interpretation of tion of peripheral loops and traces. At A, small trace; the relative position of Arachnoxylon, although it is B, C, D, three of the five large traces. X6.-Fig. 6. believed that it, along with Iridopteris and Reiman­ Xenocladia medullosina Arnold gen. et sp. nov. Longitudi­ nal view of tracheids showing wall sculpturing. X about nia, is a psilophytic derivative which had definitely . 35.-Fig. 7. X. medullosin(t Arnold gen. et sp. nov. Camera attained the primitive fern level. These three genera lucida outline sketch of transverse section of largest appear to constitute a series with Arachnoxylon specimen observed showing arrangement of individual simplest and nearest the Psilophytales, but Reiman­ steles. X6'h. nia and Iridopteris more fern-like. If the transi­ tional position of these genera is correctly postulat­ Some interesting morphological possibilities are ed, it becomes difficult to assign them to either the suggested by the xylem strand of Iridopteris. The Psilophytales or the Zygopteridaceae without ex­ structure may represent the phyllophore or leaf panding these groups to unwieldly limits. Within stalk of a type similar to that possessed by the Clad­ recent years our concept of the Psilophytales has oxylaceae or the Zygopteridaceae and which in turn lost all semblance of a natural order by the inclusion was attached to a larger stem or rhizome. Another in it of so many forms of diverse morphology, and supposition which seems more plausible is that the consequently a revision and splitting of it into sev­ axis described represents the main stalk of the plant eral orders is almost due. Because of the nebulous which in turn is homologous with the zygopterid boundaries of the Psilophytales as a group, and also phyllophore. According to this interpretation, the the fact that the three genera under consideration phyllophore would be the most primitive organ of reveal definite affinities with the zygopterid ferns, it the aerial part of the plant body. This assumption is believed that they should be classified under the seems quite in accord with the idea frequently ex­ Coenopteridales, preferably as a sub-order for which pressed that the prominently lobed xylem strands the name Iridopteridineae is proposed. This sub­ of some of the Zygopteridaceae, such as Ankyrop­ order may coincide with part of the "Protopteri­ teris or Asterochlaena, have resulted from a fusion of dales" of Zimmermann (1938), an order intended to phyllophore bases. The ultimate validity of this sup­ embrace the so-called "Primofilices" and those fern position depends upon the acquisition of more infor­ prototypes (Protopteridium, Aphyllopteris, etc.) mation. showing probable psilophytic connections. 60 AMERICAN JOURNAL OF BOTANY [Vol. 2i.

Coenopteridales, sub-order Iridopteridineae.­ Aneurophyton Hallii (Dawson) comb. nov. The sub-order Iridopteridineae is proposed for cer­ (Fig.2,3).-Dadoxylon HalliiDawson,Quart.Jour. tain fossil types which show evident psilophytalean Geol. Soc. London, 18: 306. PI. XIII, fig. 11. 1862; affinities and derivation, but which also reveal a defi­ D. Halli Dawson. Geol. Surv, Canada, p. 14. PI. I, nite trend in the direction of the ferns. Obviously, fig. 5, 6. 1871; D. d. Halli Arnold. Bull. Buffalo the group occupies an intermediate position. The fol­ Soc. Nat. Sci., 17: 2-5. PI. I, fig. 2, 3, 5, 6, 7, 8. lowing definition is built around three structurally 1935; Cordaites Halli Knowlton. Proc. U. S. Nat. preserved forms, and although its exact limits may Mus. 12: 606. 1889; C. Halli Penhallow. Proc. & be subject to modification in the future, the sub­ Trans. Roy. Soc. Canada, 6 (4): 74. 1900. order may be tentatively defined as follows: Dadoxylon H allii was first described by Dawson Stems protostelic with symmetrical, deeply fluted (1862) from fragments secured from the Tully py­ xylem strands; protoxylem mesarch, and one or more rite in Hemlock Creek, Ontario County, New York. parenchymatous areas submerged within the proto­ His description, though brief, is sufficient for identi­ xylem region near the tips of the "arms"; leaf traces, fication of the secondary wood. A few of the recently if present, simple and spirally arranged; combining discovered fragments in which the primary portion psilophytic and fern-like characteristics. of the stem is preserved (fig. 2, 3) reveal unmistak­ The foliage and fructifications are unknown. ably the same type of organizations that Krause! The concept of a group occupying an intermediate and Weyland (1929, PI. 3, fig. 8; PI. 4; PI. 5, fig. position between the ferns and Psilophytales is not 1,2) have shown in Aneurophyton. In one specimen new as a similar placement has been proposed for (fig. 2) the outline of the three-angled primary xy­ such forms as Protopieridium, Aneurophyton, Pee­ lem is strikingly revealed because of partial disin­ tinophyton, Pseudosporochnus, and Aphlebiopteris tegration of the tracheids and subsequent filling-in (Hirmer, 1938, p. 555). With the exception of Aneu­ of the cavity with mineral matter. The protoxylem rophyton, our knowledge of these forms is based was probably situated at the ends of the rather long almost entirely upon impression material. The fruc­ "arms," but whether the structure is mesarch or ex­ tifications, where known, are small spore sacs borne arch cannot be stated at present. Surrounding the terminally on small branch ramifications and similar three-angled primary xylem mass is a considerable generally to those of the typical members of the thickness of rather homogeneous secondary wood psilophyte complex such as Rhynia and Psilophyton, consisting of tracheids and narrow rays. In the spe­ but the general habit is more suggestive of ferns or cimen shown in figure 3 the three-angled primary pteridosperms in most instances. It is not yet pos­ xylem may also be recognized, although less dis­ sible to correlate evidence of relationship based upon tinctly than in figure 2 because of partial disintegra­ external appearance with that furnished by internal tion of the tissues on one side of the axis. In this structure of any of the above mentioned forms ex­ stem, the tracheids of the primary xylem are pre­ cept Aneurophyton, and consequently it is impos­ served, as are also the cortical tissues. The cortex is sible to state definitely whether any of them should approximately equal in thickness to the diameter of be included within the Iridopteridineae along with the xylem. The outer cortex contains a layer of hypo­ the structurally preserved forms. In the present dermal sclerenchyma strands separated from each treatment they are not so included, although the other by intervening parenchyma. Deeper within the possibility that some of them may ultimately find cortex are numerous smaller strands showing no spe­ their place there is freely admitted. The uncertain­ cial arrangement. Immediately surrounding "the sec­ ondary wood is a narrow zone of thin-walled cells ties involved in postulating relationship on the basis which presumably represent the phloem and cam­ of habit and structure is shown by Aneurophyton. bium. The structure of the secondary wood has been Somewhat intermediate between the ferns and Psilo­ described previously. In his original account of the phytales in habit, the internal structure of Aneuro­ species Dawson (1862) mentioned the multiseriate phyton is suggestive of neither. pitting and the numerous narrow rays. The present It is further proposed that two families be in­ author (1935) observed that the pits cover the tan­ cluded within the Iridopteridineae as follows: (a) gential as well as the radial walls of the tracheids Arachnoxylaceae, based upon the monotypic genus and also remarked upon the fact that in this respect Arachnoxylon (Read, 1938). This contains the sim­ the wood resembles that of A-neuroph.uton; pler and more psilophytic type. (b) I ridopterida­ Wood fragments of A. Hallii are the most abun­ ceae including Iridopteris, with one species and Rei­ dant plant remains in the Hamilton of western New mannia with two. This family is the more advanced York. In vertical sequence the species appears to and fern-like. range from the Murcellus shale to the Tully pyrite Were it possible to correlate forms known only which lies just beneath the Genesee shale. It has not from impressions and incrustations with the struc­ been found in the latter bed. A single fairly large turally preserved types, the Protopteridaceae, based specimen of the secondary wood from the Marcellus upon Protopteridium (Krausel, 1938, P: 499), might shale is the oldest known example of a structurally constitute a third family, but as explained above, preserved from North America. None the Iridopteridineae are limited at present to struc­ of the fragments so far observed exceed 2 em. in di­ turally preserved forms. ameter, but several are 10 em. or more in length. Feb., 1940] ARNOLD-MIDDLE DEVONIAN PLANTS 61

Usually only parts of the stems are preserved, and It is impossible to form any definite opinion con­ they are often split lengthwise so that the primary cerning the size of the complete axis, although the structure has been destroyed. largest specimen observed is about 1 em, in its broad­ The discovery of a stem in which the trilobed pri­ est dimension. Also, it is unknown whether the frag­ mary xylem strand is surrounded by secondary wood ments represent the inner or the outer tissues of with its tracheids pitted on all walls supplies the the stelar portion. Parts of at least ten steles are first positive evidence of the existence of Aneuro­ present in one specimen (fig. 7). The circular or phyton in North America. The similarity of habit somewhat elongated steles are 1 mm, or more in di­ between Aneurophyton and Eospermatopteris has ameter and are held together by ground tissue from been commented upon frequently, and both are of which all structure has disappeared. similar geological age. The original assumption that Each stele is in itself a protostele with a complete Eospermatopteris is a seed plant has been seriously zone of secondary wood (fig. 4). There is no pith, questioned because of the discovery of spores within and the very small primary xylem portion occupies some of the supposed seeds. On the other hand, the the center. The primary xylem consists only of a few stem of Aneurophyton does not exhibit fern-like tracheids with no intervening parenchyma. The sec­ structure, and its affinities are probably in the direc­ ondary xylem surrounds the primary xylem to an tion of the pteridosperms. Krausel and Weyland approximately equal depth on all sides, but its exact (1929) refer to certain resemblances between the inner limits are obscure. Viewed in transverse sec­ primary xylem strands of Aneurophyton and Steno­ tion, the secondary xylem appears to extend prac­ myelon, and the latter genus has been shown by. tically to the center. The more oval and elongated Read (1937) to be similar in several important re­ strands show evidence of branching into two ap­ spects to certain members of the Calamopityeae. proximately equal branches. Three such are shown The most striking resemblance is in the three-angled diagrammatically in figure 7. primary xylem. Whether the protoxylem of Aneuro­ Some detail of the sculpturing of the tracheid phyton is as weakly differentiated as in Stenomyelon walls is shown on the split surface (fig. 6). It is has not been determined, but in both it is confined to sometimes difficult to determine on these fractured the points of the primary mass. surfaces whether a given sculptural type is in the The primary xylem of Aneurophyton appears to primary or the secondary wood, as the limits of the be a solid mass of tracheids such as exists in the latter are indefinite, but reticulate and pitted struc­ smaller twigs of S. tuedianum (described as S. tri­ tures are clearly visible. It is assumed that the pit­ partitum by Kidston), in which in the larger stems ted walls are in the secondary wood and that the parenchyma is present as bands separating the xy­ reticulate ones are either in the primary portion or lem lobes. In S. muraium (Read, 1937) the paren­ in the innermost secondary part. The pit borders are chyma is intermixed with the tracheids to produce a not well preserved, and the shape of the apertures "mixed pith." It seems not improbable that Aneuro­ cannot be determined. In most of the pits, the cavi­ phyton may be a forerunner of the calamopityean ties are round, and the pits themselves are rather complex. During late Devonian and early Carbon­ distantly spaced, with no evidence of crowding (fig. iferous times the Calamopityeae constituted a diver­ 6 at right). In some of the tracheids the pits are sified group which was probably pteridospermous, separated vertically from each other by a space as although their position is somewhat problematic due great or greater than the diameter of the pits them­ to lack of information concerning foliage and fruc­ selves. A change from the uniseriate to the biseriate tifications. arrangement may sometimes be observed within a single trachcid. Whether the pitting in this plant is Continued investigations of the early land flor~s to be considered as revealing an advanced condition may ultimately create the necessity of removing such is questionable, although it differs rather markedly plants as Aneurophyton and Eospermatopteris from from the Dadoxylon type usually occurring in Pa­ any of the better known plant categories and placing leozoic stems. Because of the age of the plant, an ex­ them in a large plexus of synthetic types constituting tremely primitive condition is suspected. the primitive stock from which the more specialized Toward the central part of the stele scalariform forms became segregated along various lines. As is and reticulate markings are plainly evident (fig. 6 largely true of most of the purely Paleozoic plant at left), although it is unknown whether they are groups, such an assemblage would be to a consider­ confined to the primary wood or extend over into the able extent artificial and would contain forms of secondary tissue. The latter alternative seems quite diverse origin as well as the common stock of many possible in view of the limited extent of the primary later segregates. wood. At places there are indications of spiral tra­ Xenocladia medullosina gen. et sp. nov. (Fig. 4, cheids. 6, 7).-Some fragments of a very interesting poly­ In transverse section the secondary wood appears stelic axis were secured from the Tully pyrite. The dense, with small regularly arranged tracheids and plant obviously represents a new and unknown type, narrow rays. No details of ray structure are known. but because of the fragmentary condition of the ma­ Because of the fragmentary conditions Of the terial a complete description cannot be given at this material of Xenocladia medullosina, it is quiteTm­ time. possible to determine with any degree of certainty 62 AMERICAN JOURNAL OF BOTANY [Vol. 27. the affinities of this strange axis. The polystelic similar to that in Rhynia may be revealed in the ap­ structure wherein each stele is provided with an in­ parent forking of some of the steles (fig. 4, 5). dependent zone of secondary wood invites compari­ Against the psilophytalean interpretation of Xeno­ son with Cladoxylon, M etlullosa and Steloxylon. It cladia is the polystelic structure and the well devel­ differs from any known medullosan in its primary oped secondary wood. However, secondary growth, structure. A single stele of Medullosa is essentially like heterospory, seems capable of independent like that of Heterangium in which there is a large origin in almost any vascular plant group, and it central primary xylem region containing tracheids would be presumptuous to assume dogmatically that intermixed with parenchyma. Although the second­ it did not occur in at least some members of the psilo­ ary wood surrounding the primary portion may be phyte complex. Such development is actually fore­ considerable, the primary part of the medullosan shadowed in Schizopodium. Without the aid of more stem is a conspicuous feature of its internal organi­ complete material further considerations of the af­ zation. In Xenocladia there is no indication whatso­ finities of Xenocladia would be purely speculative, ever of primary structure as extensive as that of M e­ although from the bulk of evidence at hand it seems tlullosa, and in fact, the primary part of the stem is permissible to place it tentatively in the somewhat so small that it could not possibly consist of more indeterminate pteridospermous family, the Steloxy­ than a small mass of a very few tracheids. laceae. Xenocladia may ultimately prove to be a rep­ Xenocladia probably resembles Cladoxylon less resentative of some intermediate stage between the closely than it does M edullosa. Scalariform pitting Psilophytales and certain of the polystelic pterido­ is the rule in Cladoxylon, and its steles arc usually sperms. elongated in a radial direction. The main reason for SUMMARY mentioning Cladoxqlon in connection with Xeno­ cladia is that two species of the latter (C. scoparium Structurally preserved plant remains from the and C. Dawsoni) occur in the Devonian, whereas no Tully pyrite and the Ludlowville shale of upper medullosans are known there. Middle Devonian (Hamilton) age are described. Although Steloxylon is insufficiently known to Iridopteris eriensis is made the type of a new sub­ permit exact comparisons, there are certain points order, the Iridopteridineae, which is intermediate in common between it and Xenocladia. Steloxylon between the Psilophytales and the ferns. Within this resembles Xenocladia in possessing a polystelic axis sub-order are Reimannia and Arachnoxylon. Two in which some of the individual steles are circular in families, the Araclmoxylaceae and the Iridopterida­ transverse section and others are elongated. Another ceae, are distinguished. The xylem strand in the feature of probable greater significance is the fact members of the Iridopteridineae is a fluted, mesarch that the Steloxylon stele consists mainly of second­ structure with prominent "peripheral loops" near ary wood. The structure of the central portion of the extremities of the "arms." Leaf traces are pres­ the Steloxqlon stele is not well known, but as nearly ent in Iridopieris and Reimannia, and these genera as has been determined it possesses a parenchyma­ are construed as more fern-like than Arachnoxylon, tous center instead of a solid tracheid mass. The from which leaf traces are absent. Stems with sec­ main resemblance, however, is that in both forms ondary wood which occur rather abundantly in the the amount of primary development is slight as com­ Hamilton of western New York and which are de­ pared with other polystelic forms as Medullosa or scribed by Dawson as Dadoxylon Hallii are referred Cladoxylon. Xenocladia bears a further resemblance to Aneurophyton on the basis of primary structure. to Steloxylon in having bordered pits on at least Xenocladia medullosina is a polystelic axis of ob­ some of the tracheid walls. scure affinities. It contains several small protosteles The protostelic structure of the individual strands held together by a common ground mass. Each stele of Xenocladia is suggestive of a root, and the pos­ is surrounded by a complete zone of secondary xy­ sibility must be entertained that this stelar mass lem, and the primary xylem is small in amount. The belongs to a plant in which the root zone constitutes genus is tentatively referred to the Steloxylaceae. a well organized tissue outside the stem, as in Psa­ This is the oldest structurally preserved vascular ronius. Psaronius roots, however, lack secondary flora to be described from North America. growth, and it may be recalled that Paul Bertrand UNIVERSITY OF MICHIGAN, suggested that possibly Steloxylon is the root of ANN ARBOR, MICHIGAN Cladoxylon. The combination of characters ·present in Keno­ LITERATURE CITED cladia seems to be unique and without direct analogy among Paleozoic plants. That the structure is simple ARNOLD, C. A. 1935. Some new forms and new occur­ and in some respects primitive can scarcely be ques­ rences of fossil plants from the Middle and Uppcr Devonian of New York State. Bull. Buffalo Soc. tioned, and it is possible that it represents some type Nat. Sci. 17: i-rs, of undifferentiated vascular axis which is nearly on DAWSON, J. W. 186g. On the flora of the Devonian a level with the Psilophytales. The central portion period in northeastern America. Quart. Jour. GeoI. of each stele consisting as it does of a solid tracheary Soc. London 18: g96-330. mass strongly recalls that of the simple vascular HIRlIIER, M. 1938. Pteridophyta Incertae Sedis. In plants of the Rhynia type. Furthermore, branching Verdoorn, Fr. Manual of Pteridology. The ?ague. Feb., 19·10] BEETLE- 63

KRAUSEL, R. 1938. Psilophytinae. In Vcrdoorn, Fr. 1938. Some Psilophytales from the Hamilton Manual of Pteridology. The Hague. group in western. New York. Bull. Torrey Bot. _-, AND H. WEYLAND. 1929. Beltritge zur Kenntnis Club 65, 599-606. der Devonflora. III. Abh. Senken. Naturf. Gesell. ---, AND G. CAlI1PBELL. 1939. Preliminary account of 41, 315-360. the New Albany shale flora. Amer. MidI. Nat. 21, READ, C. B. 1937. The flora of the New Albany shale. 435-448. Part g. The Calamopityeae and their relationships. ZI:IBIERl\IANN, W. 1938. Phylogenie. In Verdoorn, Fr. U. S. Geol. Surv., Prof. Pap. 186-E. Manual of Pteridology. The Hague.

STUDIES IN THE GENUS SCIRPUS L. 1. DELIMINATION OF THE SU13GENERA

EUSCIRPUS AND APHYLLOIDES 1

Alan A. Beetle

SCIRPUS, A genus of the , was erected the following subgenera based upon the nature of by Linnaeus (1753) to include 24 species. Subse­ the involucre and the relative development of the quently there have been proposed in the genus ap­ cauline leaves. proximately 800 names and combinations of specific EUSCIRPUS Griseb. (emend.) Involucre of foliaceous rank. A conservative estimate as to how many of the bracts; cauline leaves usually well developed. names actually represent valid entities within the APIIYLLOIDES Involucre of non-foliaceous bracts; cauline defined generic limits of Scirpus is impossible at this leaves usually greatly reduced. time. The number 200 is frequently given. These subdivisions of approximately equal size Pax (1887) divided the genus into the subgenera conform to the natural affinities of the contained Isolepis (Link, 1821) and Euscirpus (Grisebach, groups. Scirpus sylvaticus L., the type species of the 1844) upon the absence or presence of perianth genus, must be taken as typical of the subgenus Eu­ bristles. As early as 1901 Fernald pointed out that scirpus. Since none of the numerous, already estab­ this character in itself was insufficient even for the lished subdivisions of Scirpus has used the charac­ recognition of species. Scirpus smithii Gray either ter of the involucre as a primary consideration, the lacks bristles or has mere rudiments, while in its va­ entirely new subgeneric name, Aphylloides, is given rieties seiosus Fernald and leoisetus Fassett (1921) for the group of which S. lacustris L. is typical. they are always present. Scirpus debilis Pursh has Palla (1889) studied cross-sections of the stems bristles, while in its variety ieilliamsii Fernald they of a variety of species in Scirpus and related genera, are lacking. suggesting eight genera largely based on the dis­ Again, within a widely separate series it is found tribution of vascular tissue. More recently Monoyer that Scirpus robusius Pursh has bristles variably (1934) in a comprehensive treatment of the anatomy from one to six or absent. The number of bristles oc­ of Scirpus concludes that Scirpus sylvaticus typifies curring in the related species, Scirpus paludosus the basic stock and that the derived types show two Nelson, has been reported as from one to three, two tendencies: (1) a reduction in the number of leaves to six, usually two, and none. and (2) a reduction in the vascular system. Monoyer The situation in Scirpus is apparently similar to is able on this basis to construct a family tree for the that in the genus Eleocharis (Svenson, 1929-1939) genus, placing Scirpus sylvaticus and Scirpus mari­ of the same cyperaceous tribe, Scirpeae. Many ex­ timus and their allies (his section Phylloscirpus) in amples of the variability of bristles in this genus close association as representative of the primitive may be cited. E. acicularis (L.) Roem. & Schult. has condition. From this group there have developed three to four bristles equaling the achene or bristles three general tendencies, one culminating in the sec­ .absent; in E. palustris (L.) Roem. & Schult. are tion Baeothryon (S. cespitosus and its allies), one found variously four bristles shorter than or equal­ ing the achene or absent. E. bella (Piper) Svenson in the section Eleogiton (S. fluitans and its allies) has bristles absent; E. obtusa (Willd.) Schult. has and a third leading to a rather polymorphic group including S. lacustris, S. americanus, S. mucronatus, six or seven bristles consistently present. Svenson has only rarely used perianth characters in his keys S. seiaceus, and their allies (his section Schoeno­ -e.g., in separating E. sohsoeinfurthiana Boeckler plcctus). This treatment is based solely on European (bristles present) from E. nigrescens (Nees) Steu­ material and is correlated with the ecological but not del (bristles lacking). It would be surprising if in a with the geographical distribution of the species con­ genus as close to Eleocharis as Scirpus there were cerned. Although a considerable amplification and sufficient stability in the bristles to be of significance. modification of the abbreviated phylogenetic tree of Study has shown the bristles to be highly variable as Scirpus as given by Monoyer will be necessary, the to number and character and consequently of only general treatment is in accord with the divisions limited taxonomic value. proposed in this paper. Of the four sections listed by From an examination of a large body of material Monoyer Phylloscirpus here equals Euscirpus, while the species of the genus Scirpus appear to fall into the sections Schoenoplectus, Baeothryon, and Eleo­ 1 Received for publication November 6, 1939. giton are included under Aphylloides.