RECENT WORK ON MOSSES AND FERNS. 369 



Accordingly, while we keep the sexual generation, and 

 especially the sexual organs themselves, constantly in our 

 view, we must address ourselves seriously to reconsider the 

 position as regards the sporophyte. Everybody at the 

 present day is aware of the great differences between the 

 Bryophyta and Pteridophyta. The most essential facts 

 may be summed up in a single sentence ; while all Bryo- 

 phytes have a simple form of the sporogonium, and 

 connected archesporium, Pteridophyta have differentiated 

 vegetative members, and the sporogenous tissue segregated 

 into separate cells or cell-groups. The distinction dates 

 back at least to the period of the primary rocks; obvious 

 intermediate links are absent. On grounds of comparison 

 such as those advanced by Hofmeister, botanists believe 

 that the sporogonium of the Bryophyte is truly homologous 

 with the Pteridophyte plant. But we do not know whether 

 the one was derived from the other ; they may represent 

 the results of two parallel but distinct lines of descent from 

 some remote and unknown common ancestor. Thus stated 

 the problem of origin of the more complex sporophyte 

 seems hopeless indeed, for the earth's surface has been 

 almost ransacked ; in the last quarter of a century more 

 country has been opened up for scientific inquiry than 

 perhaps in any like period before, and yet no obvious 

 connecting links have been found. As a foundation for 

 opinions we must therefore return to the study of the organisms 

 we know, and especially to those rare, isolated, and pre- 

 sumably antique types, which for various reasons we 

 believe to be nearest to the. border line. We must also 

 take into our view such testimony as the rocks are able to 

 provide. 



Examining the simpler organisms on the Bryophytic 

 side of the gulf, readers of Campbell's book will clearly 

 apprehend the process which has been at work, how a pro- 

 gressive sterilisation of cells provides vegetative tissue of 

 the sporogonium, so necessary for nutrition and dispersal of 

 the enlarging mass of spores, or, to put the matter in a 

 different terminology, certain cells in the course of descent 

 lose the faculty of undergoing the reducing of chromosomes, 



