286 SCIENCE PROGRESS. 



The method by which a simple Fern like Ophioglossum 

 may be supposed to have arisen from a structure like the 

 sporogonium of Anthoceros would be somewhat as follows. 

 From the large " foot " or absorbent organ at the base of 

 the sporogonium of the latter, by further growth an organ 

 might be formed piercing the thallus and penetrating into 

 the ground. It is extremely probable that in some such 

 way as this the first root of the vascular plants originated, 

 and so soon as this took place the sporophyte would be 

 quite independent of the gametophyte. The next step 

 would be the development of a special assimilating organ, 

 the leaf, which might be expected to arise as an outgrowth 

 from the zone of active cells between the foot and the 

 capsule in such a form as Anthoceros, which would then 

 strikingly resemble a small Ophioglossum. The vascular 

 bundles, which of course are absent, at least in their com- 

 plete form, from the sporogonium of all Bryophytes, are 

 undoubtedly directly comparable to the central strand of 

 vegetative cells which forms the columella of Anthoceros, 

 and is also found in the sporogonium of most Mosses. 

 Even in these forms this central bundle of cells probably 

 acts as a conducting tissue, although the different kinds of 

 tissue found in the bundles of the true vascular plants are 

 not yet differentiated. 



In comparing Anthoceros directly with such Pterido- 

 phytes as Ophioglosstim, it must not be supposed that a 

 direct connection between the two is assumed. There are 

 some differences so great as to forbid this. Thus the ex- 

 tremely peculiar chlorophyll bodies of all the Anthocerotese 

 are quite confined to this order, and are very different 

 from those of the Ferns. The spermatozoids, too, have 

 but two cilia, instead of the numerous ones found in all 

 true Ferns. However, in spite of these differences, the 

 resemblances are so striking that it is safe to assume 

 that the ancestor of the Pteridophytes was probably a 

 liverwort-like plant having a sporogonium essentially like 

 that of Anthoceros. 



The latest theory as to the method of origin of the 

 Pteridophytes is what may be called the "Strobiloid Theory". 



