October i, 1896] 



NA TURE 



541 



the Wealden flora, recently so carefully described by Mr. 

 Seward, one of the secretaries to this Section, has as yet yielded 

 no remains referable to Angiospernis, though this is about the 

 horizon at which we may expect their earliest trace to be found. 



Attention has already been called to the enormous antiquity 

 of the higher Cryptogams — the Pteridophyta — and to the 

 striking fact that they are accompanied, in the earliest strata in 

 which they have been demonstrated with certainty, by well- 

 characterised (lymnosperms. The Devonian flora, so far as we 

 know it, though an early, was by no means a primitive one, and 

 the same statement applies still more strongly to the plants of 

 the succeeding Carboniferous epoch. The paK-eozoic Crypto- 

 gams, as is now well known, being the dominant plants of their 

 time, were in many ways far more highly developed than those 

 of our own age ; and this is true of all the three e.xisting stocks 

 of Pteridophyta, Ferns, Lycopods, and Equisetineae. 



We cannot therefore expect any direct evidence as to the 

 origin of these groups from the paheozoic remains at present 

 known to us, though it is, of course, quite possible that the 

 plants in question have sometimes retained certain primitive 

 characters, while reaching in other respects a high development. 

 I-"or example, the general type of anatomical structure in the 

 young stems of the Lepidodendrece was simpler than that of 

 most Lycopods at the present day, though in the older trunks 

 the .secondary growth, correlated with arborescent habit, 

 produced a high degree of complexity. On the whole, however, 

 the interest of the palaeozoic Cryptogams does not con.sist in the 

 revelation of their primitive ancestral forms, but rather in their 

 enabling us to trace certain lines of evolution further upward 

 than in recent plants. From the Carboniferous rocks we first 

 learn what Cryptogams are capable of. In descending to the 

 early strata we do not necessarily trace the trunk of the 

 genealogical tree to its base ; on the contrary, we often light on 

 the ultimate twigs of extensive branches which died out long 

 before our own period. 



In a lecture which I had the honour of giving last May before 

 the Liverpool Biological Society, I pointed out how futile the 

 search for " missing links" among fossil plants is likely to be. 

 The lines of descent must have been so infinitely complex in 

 their ramilication that the chances are almost hopelessly great 

 against our happening upon the direct ancestors of living forms. 

 Among the collateral lines, however, we may find invaluable 

 indications of the course of descent. 



Fossil botany has revealed to us the existence in the Carbon- 

 iferous epocli of a fourth phylum of vascular Cryptogams quite 

 distinct from the three which have come down— more or less 

 reduced — to our own day. This is the group of Sphenophyllea;, 

 plants with slender ribbed stems, superposed whorls of more or 

 less wedge-shaped leaves, and very complex strobili with 

 stalked sporangia. The group to a certain extent combines 

 the characters of Lycopods and Horsetails, resembling the 

 former in the primary anatomy, and the latter, though remotely, 

 in external habit and fructification. Like so many of the early 

 Cryptogams, Sphenophyiliim possessed well-marked cambial 

 growth. One may hazard the guess that this interesting group 

 may have been derived from some unknown form lying at the 

 root of both Calamites and Lycopods. The existence of the 

 Sphenophyllea; certainly suggests the probability of a common 

 origin for these two series. 



In few respects is the progress made recently in fossil botany 

 more marked than in our knowledge of the affinities of the 

 Calamariex. Even so recently as the publication of 

 Count Solms-Laubach's unrivalled introduction to " Fossil 

 Botany," the relation of this family to the Horsetails was still 

 so doubtful that the author dealt with the two groups in quite 

 different parts of his book. This is never likely to happen 

 again. The study of vegetative anatomy and morphology on 

 the one hand, and of the perfectly preserved fructifications on 

 the other, can leave no doubt that the fossil Calamariese and the 

 recent F.quiseta belong to one and the .same great family, of 

 which the jiateozoic representatives are, generally speaking, by 

 far the more highly organised. This is not only true of their 

 anatomy, which is characterised by secondary growth in thick- 

 ness just like that of a Gymno.sperm, but also applies to the 

 reproductive organs, some of which are distinctly heterosporous. 

 In the genus Calamostachys we are, I think; able to trace the 

 first rise of this phenomenon. 



The external morphology of the cones is also more varied and 

 usually more complex than that of recent Equiseta, though in 

 some Carboniferous forms, as in the so-called Calamostachys 



NO. 1405. VOL. 54] 



tenuissiiua of tjrand" Eury, we find an exactly Equisetum-like 

 arrangement. 



The position of the SigillariLE as true membersof the Lycopod 

 group, is now well established. The work of Williamson proved 

 that there is no fundamental distinction between the vegetative 

 structure of Lcpidodoidroii , which has always been recognised 

 as lycopodiaceous, and that of Sigil/aria. Secondary growth in 

 thickness, the character which here, as in the case of the 

 Calamodendrei^, misled Brongniart, is the common property of 

 both genera. Then came Zeiller's discovery of the cones of 

 Sigilla'-ia, settling beyond a doubt that they are heterosporous 

 Cryptogams. A great deal still remains to be done, more 

 especially as to the relation of Sligntciria to the various types of 

 lycopodiaceous stem. At present we are perhaps too lacile in 

 accepting Sligmaria ficoidis as representing the underground 

 organs of almost any carboniferous Lycopod. 



We are now in possession of a magnificent mass of data for 

 the morphology of the pahtozoic lycopods, and have, perhaps, 

 hardly yet realised the richness of our material. I refer more 

 especially to specimens with structure, on which, here as else- 

 where, the scientific knowledge of fossil plants primarily 

 depends. 



It is scarcely necessary to repeat what has been said so often 

 elsewhere, that the now almost universal recognition of the 

 cryptogamic nature of Calamodendrere and Sigillarin; is a splendid 

 triumph for the opinions of the late Prof. Williamson, which 

 he gallantly maintained through a quarter of a century of 

 controversy. 



Perhaps, however, the keenest interest now centres in the 

 Ferns and fern-like plants of the Carboniferous epoch. No 

 fossil remains of plants are more abundant or more familiar to 

 collectors, than the beautiful and varied fern-fronds from the 

 older strata. The mere form, and even the venation of these 

 fronds, however, really tell us little, for we know how deceptive 

 such characters may be among recent plants. In a certain 

 number of cases, discovery of the fructification has come to our 

 aid, and were sori are found we can have no more doubt as to 

 the specimens belonging to true Ferns. The work of Stur and 

 Zeiller has been especially valuable in this direction, and has re- 

 vealed the interesting fact that a great many of these early Ferns 

 showed forms of fructification now limited to the small order 

 Marattiace;ia. I think perhaps the predominance of this group 

 has been somewhat exaggerated, but at least there is no doubt 

 that the marattiaceous type was much more important then than 

 now, though it by no means stood alone. In certain cases the 

 whole fern-plant can be built up. Thus Zeiller and Renault 

 have shown that the great stems known as Psaronius, the 

 structure of which is perfectly preserved, bore fronds of 

 the Pecopteris form, and that similar Pccopteris fronds pro- 

 duced the fructification of Asterotheca, which is of a marat- 

 tiaceous character. Hence, for a good many Carboniferous and 

 Permian forms there is not the slightest doubt as to their fern- 

 nature, and we can even form an idea of the particular group of 

 Ferns to which the affinity is closest. 



I will say nothing more as to the true Ferns, though they 

 present innumerable points of interest, but will pass on at once 

 to certain forms of even greater importance to the comparative 

 morphologist. 



A considerable number of pateozoic plants are now known 

 which present characters intermediate between those of Ferns 

 and Cycade;«. I say present intermediate characters, because 

 that is a safe statement ; we cannot go further than this at 

 present, for we do not yet know the reproductive organs of the 

 forms in question. 



In Lyginodeiidron, the vegetative organs of which are now 

 completely known, the stem has, on the whole, a cycadean 

 structure ; the anatomy, which is preserved with astonishing 

 perfection, presents some remarkable peculiarities, the most 

 striking being that the vascular bundles of the stem have pre- 

 cisely the same arrangement of their elements as is found in the 

 leaves of existing Cycads, but nowhere else among living plants. 

 The roots also, though not unlike tho.se of certain ferns in their 

 primary organisation, grew in thickness by means of Cambian, 

 like those of a Gymnosperm. On the other hand, the leaves of 

 Lyginodcndroii are typical fern-fronds, having the form charac- 

 teristic of the genus Sphciioptcris, and being probably identical 

 with the species S. Hwninghaitsi. Their minute structure is 

 also exactly that of a fern frond, so that no botanist would 

 doubt that he had to do with a Fern if the leaves alone were 

 before him 



