542 



NA TURE 



[OcTOliKR I, 1896 



This plant thus presents an unmistakable combination of 

 cycadian and fern-like characters. Another and more ancient 

 genus, Helerangiiiiii, agrees in many details with Lyginodeiuiroii, 

 but stands nearer the ferns, the stem in its primary structure re- 

 sembling that of a Gieic/tcnia, though it grows in thickness like a 

 cycad. These intermediate characters led Prof. Williamson and 

 myself to the conclusion that these two genera were derived from 

 an ancient stock of Ferns, combining the characters of several 

 of the existing families, and that they had already considerably 

 diverged from this stock in a cycadean direction. I believe that 

 recent investigations, of which I hope we shall hear more from 

 Mr. Seward, tend to sujiply a link between Lygiitodendroii and 

 the more distinctly cycadean stem known as Cycado.xylon. 



Heteraitginni first appears in the Burntisland beds, at the 

 base of the Carboniferous system ; from a similar horizon in 

 Silesia, Count Solms-Laubach has described another fossil, 

 Pcrolopilys Buckcana, the vegetative structure of which also 

 shows, though in a different form, a striking union of the 

 characters of Ferns and Gymnosperms. Count Solms shows 

 that this genus cannot well be included among the Lyginoden- 

 drece, but must be placed in a family of its own, which, to use 

 his own words, "increases the number of extinct types which 

 show a transition between the characters of Filicinea; and of 

 Gymnosperms, and which thus might represent the descendants 

 in difi'erent directions of a primitive group common to both." 

 (Hot. Zcitimg, 1893, p. 207.) 



Another intermediate group, quite difi'erent from either of the 

 foregoing, is that of the Medullosea;, fossils most frequent in the 

 Upper Carboniferous and Permian strata. The stems have a 

 remarkably complicated structure, built up of a number of dis- 

 tinct rings of wood and bast, each growing by its own cambium. 

 Whether these rings represent so many separate primary cylin- 

 ders, like those of an ordinary polystelic Fern, or .are entirely the 

 product of anomalous secondary growth, is still an open ques- 

 tion, on which we may expect more light from the investigations 

 of Count Solms. In any case, these curious stems (which cer- 

 tainly suggest in themselves some relation to Cycadea;) are known 

 to have borne the petioles known as Alycloxylon, which have 

 precisely the structure of cycadean petioles. (Seward, " Annals 

 of Botany," vol. vii. p. 1.) 



Renault has further brought forward convincing evidence that 

 these Myeloxylon petioles terminated in distinctly fern-like 

 foliage, referable to the form-genera Alethoptcris and Neuropleris. 

 Hence it is evident that the fronds of these types, like some 

 specimens of Spheiioptcris, cannot be accepted as true ferns, but 

 may be strongly suspected of belonging to intermediate groups 

 between Ferns and Cycads. 



It is not likely (as has been repeatedly pointed out elsewhere) 

 that any of these intermediate forms are really direct ancestors 

 of our existing Cycads, which certainly constitute only a small 

 and insignificant remnant of what was once a great class, derived, 

 as I think the evidence shows, from fern-like ancestors, probably 

 by several lines of descent. 



One of the greatest discoveries in fossil botany was un- 

 doubtedly that of the Cordaitei^ — a fourth family of Gymno- 

 sperms, quite distinct from the three now e.xisting, though having 

 certain points in common with all of them. They are much the 

 most ancient of the four stocks, extending back far into the 

 Devonian. Nearly all the wood of Carboniferous age, formerly 

 referred to Conifera: under the name of Dadoxylon or 

 Aratuayioxylon ^ belonged to these plants. Thanks chiefly to 

 the brilliant researches of Renault and Grand' Eury, the struc- 

 ture of these fine trees is now known with great completeness. 

 The roots and stems have a coniferous character, but the latter 

 contain a large, chambered pith different from anything in that 

 order. The great simple lanceolate or spatulate leaves, some- 

 times a yard long, were traversed by a number of parallel 

 vascular bundles, each of which has the exact structure of a foliar 

 bundle in existing Cycadea;. This type of vascular bundle is 

 evidently one of the most ancient and persistent of characters. 

 Both the male and female flowers (Cordaiaiithiis) are well pre- 

 served in some cases. The morphology of the former has not 

 yet been cleared up, but the stamen, consisting of an upright 

 filament bearing 2-4 long pollen-sacs at the top, is quite unlike 

 anything in Cycadeie ; a comparison is possible either with 

 Giiigko or with the Gnetacex. 



In the female flowers — small cones — the axillary ovules 

 appear to have two integuments, a character which resembles 

 Gnetacea- rather than any other Gyiunosperms. Renault's 

 famous discovery of the prothallus in the pollen-grains of 



NO 1405, VOL. 54] 



Cordaitcs indicates the persistence of a cryptogamic character ; 

 but it cannot be said that the group as a whole bears the impress 

 of primitive simplicity, though it certainly combines in a 

 remarkable way the characters of the three existing orders of 

 the Gymnosperms. 



There is one genus, Poroxyloit, fully and admirably investi- 

 gated by Messrs. Bertrand and Renault, which from its perfectly 

 preserved vegetative structure (and at present nothing else is 

 known) appears to occupy an intermediate jiosition between the 

 Lyginodendreie and the Cordaitea'. The anatomy of the stem is 

 almost exactly that of Lyginodendron, the resemblance extend- 

 ing to the minutest details, while the leaves seem to closely 

 approach those of Cordaites. Poroxylon is at present known 

 only from the Upper Carboniferous, so we cannot regard it as in 

 any way representing the ancestors of the far more ancient 

 Cordaitea;. The genus suggests, however, the possibility that 

 the Cordaitea- and the Cycadea; (taking the latter term in its 

 wide sense) may have had a common origin among forms be- 

 longing to the filicinean stock. It is also possible that the 

 Cordaitea;, or plants allied to them, may in their turn have given 

 rise to both Conifera' and Gnetacea;. 



It is unfortunate that at present we do not know the fructifica- 

 tion of any of the fossil plants which appear to he intermediate 

 between ferns and Gymnosperms. Sooner or later the discovery 

 will doubtless be made in some of these forms, and most in- 

 teresting it will be. M. Renault's Cyiadoipadix from Autun 

 appears to show that very cycad-like fructifications already existed 

 in the later Carboniferous period, and numerous isolated seeds 

 point in the same direction, but we do not know to what plants 

 they belonged. 



I think we may say that such definite evidence as we already 

 possess decidedly points in the direction of the origin of the 

 Gymnosperms generally from plants of the Fern series rather 

 than from a lycopodiaceous stock. 



I must say a few words before concluding on the cycad-like 

 fossils H hich are so striking a feature of mesozoic rocks, although 

 I feel that this is a subject with which my friend Mr. Seward is 

 far more competent to deal. Both leaves and trunks of an un- 

 mistakably cycadean character are exceedingly common in many 

 mesozoic strata, from the Lias up to the Lower Cretaceous. In 

 some cases the structure of the stem is preserved, and then it 

 appears that the anatomy as well as the external morphology is, 

 on the whole, cycadean, though simpler, as regards the course 

 of the vascular bundles, than that of recent representatives of 

 the group. 



Strange to say, however, it is only in the rarest cases that 

 fructifications of a truly cycadean type have been found in 

 association with these leaves and stems. In most cases, when 

 the fructification is accurately known, it has turned out to be of 

 a type totally different from that of the true Cycadea;, and much 

 more highly organised. This is the form of fructification 

 characteristic of Betiitcttites, a most remarkable group, the 

 organisation of which was first revealed by the researches of 

 Carruthers, afterwards extended by those of Solms-Laubach and 

 Lignier. The genus evidently had a great geological range, 

 extending from the Middle Oolite (or perhaps even older strata) 

 to the Lower Greensand. Probably, all botanists are agreed in 

 attributing cycadean affinities to the Bennettiteie, and no doubt 

 they are justified in this. Yet the cycadean characters are 

 entirely vegetative and anatomical : the fructification is as 

 difi'erent as possible from that of any existing cycad, or, for that 

 matter, of any existing Gymnosperm. At present, only the 

 female flower is accurately known, though Count Solms has 

 found some indications of anthers in certain Italian specimens. 

 The fructification of the typical species, B. Gihsoitianiis, which 

 is preserved in marvellous perfection in the classical specimens 

 from the Isle of Wight, terminates a short branch inserted 

 between the leaf-bases, and consists of a fleshy receptacle bearing 

 a great number of seeds seated on a long pedicel with barren 

 scales between them. The whole mass of seeds and intermediate 

 scales is closely packed into a head, and is enclosed by a kind of 

 pericarp formed of coherent scales, and pierced by the micro- 

 pylar terminations of the erect seeds. Outside the pericarp, 

 again, is an envelope of bracts which have precisely the structure 

 of scale-leaves in cycads. The internal structure of the seeds is 

 perfectly preserved, and strange to say, they are nearly, if not 

 quite, exalbuminous, practically the whole cavity being occupied 

 by a large dicotyledonous embryo. 



This extraordinary fructification is entirely difi'erent from that 

 of any other known group of plants, recent or fossil, and charac- 



