514 MOSSES AND FERNS chap. 



gonium became transformed into a structure directly comparable 

 to the strobilus of Phylloglossmn. The sterile leaves, as well 

 as the root, are supposed to be outgrowths of the proto- 

 corm, which latter is directly comparable to the massive foot in 

 Anthoceros, whose upper limit is the meristematic zone of cells 

 at the base of the capsule. Bower summarises his conclusions 

 as follows : ^ " The chief points which have been recognised thus 

 far, and are believed to have been the important factors in 

 advance, are: (i) sterilisation of potential sporogenous tissue; 

 (2) formation of septa ; (3) relegation of the spore-producing 

 cells to a superficial position ; and (4) eruption of outgrowths 

 (sporangiophores) on which the sporangia are supported." 



Professor Bower's explanation of the origin of the Lyco- 

 podines is certainly the most satisfactory that has yet been 

 given, and we may accept without much question his conclusion, 

 that Phylloglossuin is on the whole the simplest known Pterido- 

 phyte ; but his further conclusion that the Ferns are also prob- 

 ably reducible to a strobiloid type is by no means convincing. 



The conclusion reached by the author, after considerable 

 study of the subject, is that in the Ferns, and probably also the 

 Equisetinese, we have to deal with entirely distinct lines of 

 development. That is, while all three groups of the existing 

 Pteridophytes may be traced back to a common stock, closely 

 allied to the Anthoceroteae, the three lines became differentiated 

 at a very early period, and the differences are so great that it 

 is difficult to see how any one of them could have been derived 

 directly from either of the others. In the Lycopodineae and 

 Equisetinese the axis is developed much more strongly than the 

 leaves, and the sporophylls are usually aggregated into a more 

 or less definite strobilus. The origin of the strobilus in the 

 Equisetinese may have been similar to that in Lycopodium ; 

 but the sporangia themselves, as well as the structure of the 

 tissues and the prothallium, are more like those of the Ferns, 

 and make it extremely improbable that the strobilus is homo- 

 logous with that of the Lycopodinese. In the very definite 

 apical growth of the stem and root, as well as in the structure 

 and arrangement of the vascular bundles, Equisetuni approaches 

 much more nearly the condition found in OpJiioglossitin than 

 that of the Lycopodinese ; and the large multiciliate spermato- 

 zoids, and the early divisions of the embryo, are also suggestive 



1 Bower (16), p. 360. 



