56 Morphology BOOK i 



evidence, and clearing up so fully many difficult points of 

 structure, that his investigations are fully worthy of being 

 placed side by side with those of Hofmeister fifty years 

 before. It may be added, parenthetically, that his later 

 work did not lead him to modify in any material point 

 the views he expressed in 1890, to which we must now 

 turn. 



Bower's views may be summarized as follows : He set 

 out by restating the conclusions of Braun and of Cela- 

 kowsky that the gametophyte of the antithetic phase is the 

 original form of the plant, and claimed that the sporophyte 

 is a stage that has been gradually intercalated between 

 two successive sexual generations. The development of 

 the sporophyte has been produced by amplification of the 

 zygote. The subdivision of the latter into numerous cells 

 has brought about, as the effect of a single sexual fusion, 

 the possibility of a large number of offspring. This practi- 

 cally amounts to a kind of polyembryony, as was suggested 

 in 1887 by Vaizey. The cells when isolated are the struc- 

 tures we recognise as spores or carpospores. The spore- 

 producing multicellular body so made by the subdivision 

 of the zygote was all sporogenous at first, but as its size has 

 increased a progressive sterilization of its tissues has followed, 

 so that the production of spores has become confined to part 

 of it, the rest being sterile or vegetative. No doubt the 

 formation of a wall to the mass, seen in Riccia as already 

 noted, was the beginning of this process. The group of 

 the Bryophyta shows us a series of plants in which pro- 

 gressive sterilization is closely connected with increasing 

 size and structural complexity. Starting with the condition 

 in Riccia we find sterile cells, elaters, &c., making their 

 appearance in the mass of sporogenous cells, the gradual 

 formation of a central columella, and the differentiation 

 of a more actively vegetative part, the apophysis, at the 

 base of the whole sporogonium, together with the further 



