﻿WHITE] FOSSIL PLANTS 01 i ' ' P iDOFILICES 3^9 



only "ii petrified stems, such for example as Cladoxylon and Calamo- 

 pitySj which differ essentially Erom ferns only by the presence of 

 their secondary wood. It must al>o be remembered that both sec- 

 ondary wood, of a sort, and collateral bundles are found in the 

 Ophioglossacese. 



Conclusions 



The development of secondary xylem in various Cryptogamic 

 families among Carboniferous plants, in various species of the same 

 genus, and at various stages and positions, in the growth of the plant 

 conclusively supports the view, long ago suggested by Williamson 

 in the case of Catamites, that secondary wood originated as an engi- 

 neering feature — a mechanical aid for the support of the gigantic 

 Carboniferous representatives of some of our humble modern fam- 

 ilies. As such its origin was doubtless polyphyletic and, naturally, 

 since the types appeared in different geological stages, polychronous. 



The varied phases in which this secondary wood appeared — in 

 polystelic, inverted intra-medullary, extra-fascicular or accessory, 

 and laterally alternating-, as well as modern phases, with their re- 

 markable differences in combination, and in varying degrees of com- 

 plication- — constitute a group of structural anomalies which in them- 

 selves offer the evolutionist strong testimony of fortuitous variation. 

 It is as though Nature were at the Carboniferous moment in the 

 midst of a series of amazing engineering experiments, most of which 

 were either buried deep in Paleozoic oblivion, or permitted to survive 

 only as vestigial relics and atavistic ghosts. , 



Our knowledge of the structures and fructifications of the Cycado- 

 filices (Pteridospermese) leaves little room for doubt as to the descent 

 of the Cycads, and perhaps some of the other modern gymnosperm- 

 ous types, 1 from the ferns, though, as Doctor Scott has taken pains 

 to point out, it does not follow that any of the Coal Measure types 

 yet discovered actually represent the lineal ancestors of our living 

 gymnospermic genera. 



The discovery of seed-bearing members of the Cycadofilices, while 

 answering in part the old question as to the origin of the gymno- 

 sperms, injects, at the same time, a new biological problem into the 

 field of inquiry, — viz., the origin of the Cycadofilices. Seeds of so 

 high and so gymnospermoid an organization as Lagenostoma or 



1 There is important data in support of the view that >a portion, at least, 

 of the conifers were derived from the Paleozoic Lycopodiales through a 

 group of Lycopodineous seed plants whose existence is predicated partly 

 on paleontological indications, partly on theoretical grounds, rather than defi- 

 nitely known or established, and for which Professor Ward (Science, Aug. 

 26, 1904, p. 281) has proposed the class term " Lepidospermse." 



