RECENT WORK ON MOSSES AND FERNS. 365 



and of the sporophyte to the background, and pass over the 

 direct effect which external conditions have in modifying 

 the form of the parts upon which our comparison mainly 

 rests, this conclusion may appear satisfactory, and we may 

 continue to regard the Mosses and Filmy Ferns as the 

 nearest points of contact across the gulf which separates 

 the Bryophyta from the Pteridophyta. But before accept- 

 ance of this position it will be necessary (1) to be sure 

 that the characters upon which the comparison rests are 

 reasonably constant, and (2) to be sure that the characters 

 which we put only in the second place are really less im- 

 portant. 



As early as 1888 the want of constancy of the 

 vegetative characters of the prothallus in Trichomanes had 

 been remarked upon (Bower, Annals of Botany, vol. i., p. 

 289, etc.). It was pointed out that " abnormal external 

 conditions may largely control the vegetative development 

 of the oophyte " (/. e., p. 292), and that, therefore, in deal- 

 inor with the decadent sexual Generation, even greater 

 caution would be necessary than in comparison of the 

 nascent sporophyte. The inconstancy of form of the 

 protonema in Mosses, and occurrence of flattened ex- 

 pansions in certain species, were a matter of old observation. 

 The opinions based on these and other isolated observa- 

 tions have since been fully justified by the excellent work 

 of Klebs {Biologisches Centralblatt, p. 640, 1893): this 

 author has shown by cultures how direct is the influence 

 of light upon the conformation of the gametophyte, and 

 that the filamentous form can be extended or checked 

 according to the intensity of the light to which the grow- 

 ing organism is exposed. We are thus driven to conclude that 

 that which is so readily and directly mutable at the present 

 day cannot be accepted as in itself sufficient evidence of a 

 phylogenetic history which dates back, as the origin of 

 Ferns certainly does, to a time prior to the Devonian 

 period. 



The comparisons based upon the filamentous character 

 do not accord with those of the sexual organs ; for instance, 

 though the filamentous protonema of Buxbaumia may 



