282 SCIENCE PROGRESS. 



structure of the sporophyte, the comparison of the fila- 

 mentous prothallium of Trichomanes with the protonema of 

 a Moss is hardly convincing, as the former is homologous 

 not with the protonema alone, but with the protonema plus 

 the leafy stem, and the Moss Buxbaumia, which he considers 

 the most primitive in that the leafy stem is extremely re- 

 duced, is known to be saprophytic, and this abnormal habit 

 is quite sufficient to account for the great reduction of the 

 vegetative organs of the gametophyte. 



While the filamentous prothallium of some species of 

 Trichomanes is certainly strikingly like a Moss protonema, 

 other species have the flat prothallium like that of other 

 Ferns, and this is always the case with normally developed 

 prothallia of all species of the closely-relative genus 

 Hymenophyllum. These differences might be explained if 

 we had to consider only the prothallium, but when in addi- 

 tion the character of the sporophyte is taken into account 

 it becomes impossible to reconcile the radical differences 

 between the simplest forms of the Hymenophyllaceae and 

 any known Bryophyte. 



The forms of the Bryophytes whose protonemata most 

 resemble the prothallium of Trichomanes are all specialised 

 types whose sporogonia are very far removed indeed from 

 the simple character that would be expected in primitive 

 forms, while all the Bryophytes whose sporogonia can in 

 any way be considered primitive are thallose, and much 

 more like the flat prothallium of the majority of Ferns ; 

 this, in connection with the great similarity in the method 

 of growth of the two, makes it seem much more, likely that 

 the older view of the origin of the Ferns from forms like 

 the thallose Hepaticae is correct. This seems the more 

 probable as a study of the sexual organs shows much in 

 common between some of the thallose Liverworts and 

 certain Ferns, while all the true Mosses differ much from 

 the latter in this respect. 



Botanists at present usually divide the Ferns into two 

 main divisions, the Eusporangiatseandthe Leptosporangiatse, 

 the distinction being based upon the character of the 

 sporangia. In the latter group, which comprises an 



