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e oldest known representatives of the Equisetales the leaves were highly developed and dichotomously divided； thus differing greatly from the mere scale…leaves of the recent Horsetails； or even from the simple linear leaves of the later Calamites。 The early members of the class； in their forked leaves； and in anatomical characters； show an approximation to the Sphenophyllales； which are chiefly represented by the large genus Sphenophyllum； ranging through the Palaeozoic from the Middle Devonian onwards。 These were plants with rather slender； ribbed stems； bearing whorls of wedge…shaped or deeply forked leaves； six being the typical number in each whorl。 From their weak habit it has been conjectured； with much probability； that they may have been climbing plants； like the scrambling Bedstraws of our hedgerows。 The anatomy of the stem is simple and root…like； the cones are remarkable for the fact that each scale or sporophyll is a double structure； consisting of a lower； usually sterile lobe and one or more upper lobes bearing the sporangia； in one species both parts of the sporophyll were fertile。 Sphenophyllum was evidently much specialised； the only other known genus is based on an isolated cone； Cheirostrobus； of Lower Carboniferous age； with an extraordinarily complex structure。 In this genus especially； but also in the entire group； there is an evident relation to the Equisetales； hence it is of great interest that Nathorst has described； from the Devonian of Bear Island in the Arctic regions； a new genus Pseudobornia； consisting of large plants； remarkable for their highly compound leaves which； when found detached； were taken for the fronds of a Fern。 The whorled arrangement of the leaves； and the habit of the plant； suggest affinities either with the Equisetales or the Sphenophyllales； Nathorst makes the genus the type of a new class； the Pseudoborniales。 （A。G。 Nathorst； 〃Zur Oberdevonischen Flora der Baren…Insel〃； 〃Kongl。 Svenska Vetenskaps…Akademiens Handlingar〃 Bd。 36； No。 3； Stockholm； 1902。）
The available data； though still very fragmentary； certainly suggest that both Equisetales and Sphenophyllales may have sprung from a common stock having certain fern…like characters。 On the other hand the Sphenophylls； and especially the peculiar genus Cheirostrobus； have in their anatomy a good deal in common with the Lycopods； and of late years they have been regarded as the derivatives of a stock common to that class and the Equisetales。 At any rate the characters of the Sphenophyllales and of the new group Pseudoborniales suggest the existence； at a very early period； of a synthetic race of plants； combining the characters of various phyla of the Vascular Cryptogams。 It may further be mentioned that the Psilotaceae； an isolated epiphytic family hitherto referred to the Lycopods； have been regarded by several recent authors as the last survivors of the Sphenophyllales； which they resemble both in their anatomy and in the position of their sporangia。
The Lycopods； so far as their early history is known； are remarkable rather for their high development in Palaeozoic times than for any indications of a more primitive ancestry。 In the recent Flora； two of the four living genera （Excluding Psilotaceae。） （Selaginella and Isoetes） have spores of two kinds； while the other two （Lycopodium and Phylloglossum） are homosporous。 Curiously enough； no certain instance of a homosporous Palaeozoic Lycopod has yet been discovered； though well…preserved fructifications are numerous。 Wherever the facts have been definitely ascertained； we find two kinds of spore； differentiated quite as sharply as in any living members of the group。 Some of the Palaeozoic Lycopods； in fact； went further； and produced bodies of the nature of seeds； some of which were actually regarded； for many years； as the seeds of Gymnosperms。 This specially advanced form of fructification goes back at least as far as the Lower Carboniferous； while the oldest known genus of Lycopods； Bothrodendron； which is found in the Devonian； though not seed…bearing； was typically heterosporous； if we may judge from the Coal…measure species。 No doubt homosporous Lycopods existed； but the great prevalence of the higher mode of reproduction in days which to us appear ancient； shows how long a course of evolution must have already been passed through before the oldest known members of the group came into being。 The other characters of the Palaeozoic Lycopods tell the same tale； most of them attained the stature of trees； with a corresponding elaboration of anatomical structure； and even the herbaceous forms show no special simplicity。 It appears from recent work that herbaceous Lycopods； indistinguishable from our recent Selaginellas； already existed in the time of the Coal…measures； while one herbaceous form （Miadesmia） is known to have borne seeds。
The utmost that can be said for primitiveness of character in Palaeozoic Lycopods is that the anatomy of the stem； in its primary ground…plan； as distinguished from its secondary growth； was simpler than that of most Lycopodiums and Selaginellas at the present day。 There are also some peculiarities in the underground organs （Stigmaria） which suggest the possibility of a somewhat imperfect differentiation between root and stem； but precisely parallel difficulties are met with in the case of the living Selaginellas； and in some degree in species of Lycopodium。
In spite of their high development in past ages the Lycopods； recent and fossil； constitute； on the whole； a homogeneous group； and there is little at present to connect them with other phyla。 Anatomically some relation to the Sphenophylls is indicated； and perhaps the recent Psilotaceae give some support to this connection； for while their nearest alliance appears to be with the Sphenophylls； they approach the Lycopods in anatomy； habit； and mode of branching。
The typically microphyllous character of the Lycopods； and the simple relation between sporangium and sporophyll which obtains throughout the class； have led various botanists to regard them as the most primitive phylum of the Vascular Cryptogams。 There is nothing in the fossil record to disprove this view； but neither is there anything to support it； for this class so far as we know is no more ancient than the megaphyllous Cryptogams； and its earliest representatives show no special simplicity。 If the indications of affinity with Sphenophylls are of any value the Lycopods are open to suspicion of reduction from a megaphyllous ancestry； but there is no direct palaeontological evidence for such a history。
The general conclusions to which we are led by a consideration of the fossil record of the Vascular Cryptogams are still very hypothetical； but may be provisionally stated as follows：
The Ferns go back to the earliest known period。 In Mesozoic times practically all the existing families had appeared； in the Palaeozoic the class was less extensive than formerly believed； a majority of the supposed Ferns of that age having proved to be seed…bearing plants。 The oldest authentic representatives of the Ferns were megaphyllous plants； broadly speaking； of the same type as those of later epochs； though differing much in detail。 As far back as the record extends they show no sign of becoming merged with other phyla in any synthetic group。
The Equisetales likewise have a long history； and manifestly attained their greatest development in Palaeozoic times。 Their oldest forms show an approach to the extinct class Sphenophyllales； which connects them to some extent； by anatomical characters； with the Lycopods。 At the same time the oldest Equisetales show a somewhat megaphyllous character； which was more marked in the Devonian Pseudoborniales。 Some remote affinity with the Ferns （which has also been upheld on other grounds） may thus be indicated。 It is possible that in the Sphenophyllales we may have the much…modified representatives of a very ancient synthetic group。
The Lycopods likewise attained their maximum in the Palaeozoic； and show； on the whole； a greater elaboration of structure in their early forms than at any later period； while at the same time maintaining a considerable degree of uniformity in morphological characters throughout their history。 The Sphenophyllales are the only other class with which they show any relation； if such a connection existed； the common point of origin must lie exceedingly far back。
The fossil record； as at present known； cannot； in the nature of things； throw any direct light on what is perhaps the most disputed question in the morphology of plantsthe origin of the alternating generations of the higher Cryptogams and the Spermophyta。 At the earliest period to which terrestrial plants have been traced back all the groups of Vascular Cryptogams were in a highly advanced stage of evolution； while innumerable Seed…plantspresumably the descendants of Cryptogamic ancestorswere already flourishing。 On the other hand we know practically nothing of Palaeozoic Bryophyta； and the evidence even for their existence at that period cannot be termed conclusive。 While there are thus no palaeontological grounds for the hypothesis that the Vascular plants came of a Bryophytic