114 



NA TURE 



[May 30, 1907 



nothing of the nature of a flower is differentiated. No 

 other living seed-plant is so primitive as this, but the 

 cycads as a whole are undoubtedly the most primitive 

 family of present-day Spermophyta, as is most strikingly 

 shown in their cryptogamic mode of fertilisation by means 

 of spermatoEOids, which they share with Ginkgo alone 

 among seed-plants. 



When we go back to the Mesozoic age we might, on 

 what one may call the elementary view of evolution, expect 

 to find the Cycadophytes, which were so abundant at that 

 period, still simpler and still nearer the cryptogamic con- 

 dition than the members of the class which have come 

 down to our own day. But this is by no means the case ; 

 there were, no doubt, a certain number of cycads in 

 Mesozoic times which were about on the same level of 

 organisation as their living representatives, but the great 

 majority, so far as the available evidence shows, attained 

 a much higher organisation, at least in their reproductive 

 arrangements, far surpassing any of 

 the gymnosperms now known to us. 

 This is one of the many facts in 

 paleontology which show that evolu- 

 tion is by no means the obvious pro- 

 gression from the simple to the com- 

 plex which many people have imagined. 

 Just as the lycopods and the horsetails 

 of the Coal-measures were not simpler, 

 but far more complex than their 

 successors, so the Cycadophyta of 

 Mesozoic age were, on the whole, on 

 a much higher level than the surviving 

 family Cycadaceas, which now repre- 

 sents them. The history of the vege- 

 table kingdom, so far as its records are 

 known, is the history of the ascerrd- 

 ancy of a succession of dominant 

 families, each of which attained at 

 some definite period its maximum, both 

 in extent and organisation, and then 

 sank into comparative obscurity, or 

 died out altogether, giving place to 

 some other race, which, under chang- 

 ing conditions, was better able to 

 assume the leading idle. The cycado- 

 phytes of the Mesozoic were, in their 

 day (and it was a long one), a 

 dominant group, almost as much so as 

 the dicotyledons are now, and they 

 equipped themselves with a correspond- 

 ingly high organisation, even rivalling 

 the angiospermous flowering plants 

 (perhaps cadets of the same stock), 

 which ultimately displaced them. 



Among the Mesozoic Cycadophyta 

 there were some, as already mentioned, 

 which seem to have been essentially 

 similar to our recent cycads. I do not, 

 however, propose to dwell on this line 

 of descent, but will now pass on to 

 those Mesozoic Cycadophyta which 

 attained a higher level of organisation, 

 giving them a better title to the name 

 of ■' flowering plants " than any of their predecessors or 

 contemporaries. 



The genus Bennettites was founded by Carruthers in 

 1868 ' for certain cycadean stems, of Oolitic and Lower 

 Cretaceous age, with fruits borne on secondarv axes, not 

 protruding beyond the bases of the petioles. The species 

 on which, for many years, our Icnowledge of the group 

 was principally based is Bctmetlites Gibsonianus, of 

 which a magnificently preserved specimen was discovered, 

 just fifty years ago, in the Lower Greensand of Luccombe 

 Chine, in the Isle of Wight. Some years later a second 

 specimen was found in the same locality, but no others 

 have as yet come to light. In B. Gibsonianus and other 

 species the external appearance of the stem was similar 

 to th.'it of many recent cycads, its surface being com- 

 pletely invested by an armour of persistent leaf-bases. 

 Anatomically, there is also a marked agreement, the chief 



1 " On Fossil Cycidean Stems ("roin the Secondary Rods of Brit.iin.'' 

 Tr.-ins. Linn. Soc. London, xxvi. 



NO. 1 96 1, VOL. 76] 



distinction consisting in the simpler course, in the case 

 of the fossil, of the vascular strands which pass out from 

 the stem into the leaves. A striking feature is the 

 presence, in great numbers, on the leaf-bases and bracts, 

 of flat, scaly hairs, of the same nature as the ramenta 

 characteristic of ferns. Even in external appearance, how- 

 ever, a Bennettitean slem, if in the fruiting condition, 

 differs conspicuously from that of any recent cycad in the 

 presence of a number of short, lateral branches, like large 

 buds, wedged in between the leaf-bases, and arising in 

 their axils (see Fig. i, from an American species). These 

 bodies are the fructifications, the characteristic feature of 

 the Bennettitea:. In structure, as well as in position, they 

 differ totally from any form of fructification met with in 

 recent cycads or other gymnosperms. 



The peduncle bears many spirally arranged bracts, which 

 completely enclose the fructification. The end of this 

 peduncle expands into a ( oiufx receptacle, on which organs 



Fig. I. — Cycadeoldea 

 original daguerr' 

 groups of bract ; 

 From Wieland's 



jriayyhtftJica. The earliest described American fossil Cycad. From an 

 :otype. Nearly thirty young fruits are marked in the present view by the 

 cars interpolated between the old leaf-bases. About one-fourth natural size. 

 Fossil Cycads." 



of two kinds are borne, the one fertile, the other sterile. 

 The fertile appendages consist each of a long, slender 

 pedicel, terminating in a single orthotropous seed, with the 

 micropyle directed outwards. The seed-bearing pedicels are 

 present in large numbers ; the sterile appendages, or inter- 

 seminal scales, are still more numerous. They form a dense 

 packing between the seed-pedicels, and somewhat overtop 

 the seeds themselves, expanding at their apices to form an 

 almost continuous envelope, leaving only small perfor- 

 ations, into which the micropylar ends of the seeds are 

 fitted. They form colleclively a kind of pericarp, differ- 

 ing, however, from that of an angiospermous fruit in the 

 presence of openings for the micropyles of the seeds. The 

 whole complex fruit is enclosed in the mantle of over- 

 lapping bracts. In Bennettites Gibsonianus the fruits dis- 

 covered are practically ripe, for each seed contains a large 

 dicotyledonous embryo, with somewhat fleshy cotyledons. 

 The embryo almost fills the seed, which was thus nearly, 

 if not quite, cxalbuminous — an unprecedented condition in 



