Septembbe 23, 1898.] 



SCIENCE. 



379 



become increasingly apparent that gymno- 

 sperms are very closely related to pterido- 

 phytes. It was natural, for a time, to 

 regard gj^mnosperms as phylogenetically 

 intermediate between pteridophytes and 

 angiosperms, for it was not easy to believe 

 that such a structure as the seed appeared 

 in more than one genetic line ; but it is 

 probably not going too far to say that there 

 is now no serious opposition to the view 

 that the gymnosperm and angiosperm lines 

 are genetically independent. However, 

 such a discussion does not lie within the 

 scope of this paper. 



That gymnosperms have been derived 

 from pteridophyte stock is hardly open to 

 discussion; at least we must assume that 

 this is true, or all attempts at phylogeny 

 are useless. The iirst question which con- 

 fronts us, therefore, is whether the very 

 divergent gymnosperm lines have had a 

 common origin in this pteridophyte stock 

 or not. Was there a single group of archaic 

 gymnosperms, derived from pteridophytes, 

 which subsequently differentiated into dis- 

 tinct lines? The existing gymnosperm 

 groups are so very diverse that one of two 

 things seems evident : either they differen- 

 tiated into divergent lines from a common 

 gymnosperm stock in very ancient times, or 

 they originated independently from the 

 pteridophyte stock. From this discussion I 

 wish to exclude the Gnetales, as we do not 

 possess suflBcient data concerning their early 

 history, or concerning the morphology of 

 the very dissimilar living forms, to justify 

 any opinion as to their origin. They are 

 such dissimilar fragments, living in such 

 extreme conditions, that their origin is 

 totallj' obscure. In some respects they are 

 more cycad-like than conifer-like, but in 

 most respects they are so unlike both that a 

 separate origin seems possible. It may be 

 even true that the three genera belong to 

 groups of independent origin, which is cer- 

 tainly the easiest way of disposing of their 



differences ; and their common characters 

 of true vessels, the so-called perianth and 

 elongated micropyle, may have been at- 

 tained independently as readily as heteros- 

 pory ; but the combination of characters in 

 common does not seem to justifj^ such a dis- 

 position of them, and the three genera had 

 better be regarded as of common derivation, 

 wonderfully diversified by ancient separa- 

 tion, isolation and extreme conditions. 



Approaching the subject from the his- 

 torical standpoint, the group Cordaites 

 seems to be the first with sufiBcient data to 

 justify consideration. The structure of the 

 vascular bundles, especially those of the 

 leaves, is said to suggest those of conifers, 

 cj'cads, Isoetes and Ophioglossum ; and the 

 sporophylls are organized into a strobilus, a 

 character common to pteridophytes and 

 gymnosperms. But such characters can be 

 used only as cumulative testimony. In 

 such evidences as we have of the structure 

 of the male gametophyte, however, we ob- 

 tain some valuable suggestions. Within 

 the mature microspore there appears a con- 

 siderable group of polygonal cells. In liv- 

 ing groups of gymnosperms, so far as in- 

 vestigated, there is no such structure ; and 

 if we look to pteridophytes for suggestion 

 we are constrained to believe that this group 

 of cells is either prothallial or sperm mother 

 cells. In either event, it would represent 

 a condition of things much nearer pterido- 

 phytes than is shown by any living seed 

 plant. In view of the discovery of sperma- 

 tozoids in Cycas, Zamia and Ginkgo, taken 

 ia connection with the peculiar structure of 

 the male gametophyte just described, I am 

 of the opinion that the Cordaites also de- 

 veloped spermatozoids. With either hypoth- 

 esis as to the nature of the cells developed 

 within the microspore of Cordaites, in seek- 

 ing for the pteridophyte origin of the group, 

 we are led away from such heterosporons 

 pteridophytes as now exist, for in them the 

 male gametophyte is much more reduced 



