344 Causes and Course of Organic Evolution 



phological gap between the simpler cellular groups, like those 

 already studied, and the vascular plants, it must be accepted 

 that still the gap is an enormous one. The problem is also 

 further com])licated by our knowing that there existed, through- 

 out the geologic period that extends from the upper devonian 

 to the lower permian, extensive groups of vascular plants that 

 attained to huge size, as compared with living representatives. 

 Their extreme abundance, comphcated structure, and capacity 

 for reproduction were all so pronounced that alongside them 

 their representatives now existing are truly starved remnants. 

 So true is this that the devonian and carboniferous epochs 

 together have been spoken of as "the age of vascular cryp- 

 togams." 



We are compelled therefore to accept that during the Cam- 

 brian and silurian epochs numerous transition genera between 

 algoid and vascular plants evolved, gave rise in some cases 

 to higher forms than themselves, and in turn were blotted 

 out. In the process, some of the higher types for a time sur- 

 vived, and originated still higher organisms, thereafter dis- 

 appearing like their progenitors. 



Though the position may be a mistaken one, we incline to 

 accept the biciliate and polyciliate structure of the mature 

 spermatozoid as a useful guide in determining affinities. Ac- 

 cordingly, in line TN-ith the biciliate coleochsetoid and bryo- 

 phytic groups reviewed above, we now pass to the vascular 

 series of the Lycopodineae, or club mosses, and the Psilotinese 

 of minor im])ortance at the present day. Thereafter starting 

 with the polyciliate type Aphanochcete we shall advance to 

 the fern, the horsetail, the fern-tycad, and higher alliances. 



The group Lycopodinese, that includes the living genera 

 Lycopodium and Selaginella with a considerable number of 

 species, and Phylloglossum with one species, will mainly con- 

 cern us. 



When the spore of Lycopodium cernuum bursts it produces 

 a cylindric tube, which we would again regard as the homo- 

 logue of the swarmspore tube of Coleochcete. This divides 

 into three to six cells by transverse walls, and so forms a proto- 

 nema that is of green color. At its extremity a subterminai 



