XV S UMMA RY AND CONCL US IONS 



3'3 



of the Ferns rather than of the Lycopods. Of course the fact 

 that our knowledge of the Equisetineai is mainly based upon 

 the single genus Equisettun, makes it unsafe to lay too much 

 stress upon conclusions drawn from a study of this single type. 

 However, such of the fossil forms as show unmistakable evidence 

 of belonging to the Equisetinec-e, conform closely in their 

 structure, so far as it is known, to the living types. 



In the Filicines the development of the leaves is usually 

 much greater than in either of the other classes, and the origin 

 of the sporophyll is probably different. Bower considers the 

 sporophyll of Ophioglossiini, for example, as the homologue of 

 a single sporophyll of Lycopodiicin, and the whole sporangial 

 spike as equivalent to a single sporangium. With this view the 

 author feels that he cannot agree, and it seems more likely that 

 the origin of the Fern-type of sporophyte was quite different 

 from that of the Lycopodineae, and that there is nothing among 

 the Ferns comparable to the strobilus of the latter. 



If we could imacrine the meristem at the base of the 

 sporogonium of AntJioceros to produce a lateral flattened 

 appendage or leaf, and the foot to develop into a root penetrat- 

 ing the thallus into the earth, we should have a structure not 

 very unlike a small OpJiioglossuin. In this case the sporangial 

 spike would represent, not a single sporangium of P/iylloglosstnn, 

 but the whole strobilus, and the sterile segment of the leaf 

 would then be comparable rather to the sterile leaves (proto- 

 phylls) than to a single sporophyll. 



While the Lycopodineae correspond closely to the Bryo- 

 phytes in the form of the spermatozoids, these in the other 

 Pteridophytes are large and multiciliate. Whether these 

 peculiarities have arisen independently in the Filicinese and 

 Equisetineee, or whether they are inherited from some common 

 ancestor, there is no means of deciding. None of the Muscineje, 

 so far as is known, depart from the biciliate type, but among 

 Alg^e, Q^dogoniuvi offers a similar exception to the usual 

 biciliate form. 



The Lycopodiaceai and Selaginelles constitute a sufficiently 

 direct series, but the exact affinity of the Psilotaceae to these is 

 by no means clear. Our complete ignorance of the sexual 

 stage of the latter, as well as their parasitic habit, makes it 

 impossible to judge just how far their simple structure is 

 primary and how much is due to reduction. 



