XVII SUMMARY AND CONCLUSIONS 599 



he conceives that the smooth cyh'nch'ical si^orogonium l^ecame 

 transformed into a structure (hrectly comparable to the strol)ikis 

 of Phylloglossiim. The sterile leaves, as well as the root, are 

 supposed to be outgrowths of the protocorm, which latter is 

 directly comparable to the massive foot in AntJwccros, 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 be- 

 lieved 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 super- 

 ficial position; and (4) eruption of outgrowths (sporangio- 

 phores) on which the sporangia are supported." 



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

 podineje is certainly the most satisfactory that has yet been 

 given, and we may accept without much c[uestion his conclusion, 

 that PhyUoglossuin 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 probal}ly also the 

 Equisetine?e, we have to deal with entirely distinct lines of 

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

 Pteridophytes may perhaps be traced back to a common stock, 

 closely allied to the Anthocerotes, the three lines became differ- 

 entiated 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 Lycopo- 

 din.ecHs and Equisetineae the axis is developed much more 

 strongly than the leaves, and the sporophylls are usually aggre- 

 gated into a more or less definite strobilus. The origin of the 

 strobilus in the Equisetine?e may have been similar to that in 

 Lycopodimn: but the sporangia themselves, as well as the struc- 

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

 the Ferns, and make it extremely improbable that the strobilus 

 is homologous with that of the Lycopodine?e. In the very defi- 

 nite apical gTowth of the stem and root, as well as in the 

 structure and arrangement of the vascular bundles, Eqiiisctiiin 

 approaches much more nearly the condition found in OpJiioglos- 

 snm than that of the Lycopodineae ; and the large multiciliate 

 spermatozoids, and the early divisions of the embryo, are also 



