THE ORIGIN OF THE VASCULAR PLANTS. 287 



This assumes that the forms like Lycopodium and 

 Equisetimi, in which the sporophyte forms a strobilus, or 

 cone, are the most primitive. Professor Bower, who has 

 advanced this theory, bases his conclusions upon a most 

 thorough study of a very large number of forms, and his 

 arguments are very convincing, at least so far as concerns 

 the really strobiloid forms. In regard to the Ferns, there 

 are some serious difficulties in the way. This theory 

 assumes, as does the one just considered, that the ancestor 

 of the Pteridophytes was a form like Anthoceros, with a 

 continuous hypodermal archesporium, and that this in turn 

 was derived from simpler forms in which the sporogenous 

 tissue was much more prominent. The first step in the 

 development of the strobilus was the segregation of the 

 sporogenous cells by masses of sterile tissue, exactly as we 

 have supposed in the evolution of Ophioglossum. Instead, 

 however, of this sterile tissue simply forming the partitions 

 between the sporangia, it is supposed to have developed 

 into outgrowths or leaves, so that corresponding to each 

 leaf there was a separate sporangium such as is found in 

 Lycopodium. The form which Professor Bower considers 

 to come nearest the primitive condition is a curious little 

 lycopodinous plant, Phylloglossum. This interesting form 

 shows certain striking resemblances to the embryo of various 

 species of Lycopodium, the common club mosses, and seems 

 to have retained its primitive or embryonic condition. 

 From such a type as this the other Lycopodineae are 

 supposed to have descended. 



Professor Bower is inclined to regard all of the 

 Pteridophytes as reducible to a strobiloid form, but as 

 far as the Ferns are concerned there are very 

 serious difficulties in the way. Aside from apparently 

 essential differences in the sporophyte between Ferns and 

 Lycopods, there are also differences in the gametophyte 

 which cannot readily be explained on the ground of a 

 common origin. The most essential difference is in the 

 spermatozoids. These in the Lycopodineae are bi-ciliate 

 like all known Muscineae, while in the Ferns and Equiseta 

 they are multi-ciliate. It is quite conceivable, nay, probable, 



