THE NATURE OF ALTERNATION, ETC. 329 



may be mentioned, since in it we find the first steps 

 made in the experimental study of the gametophyte of 

 mosses and ferns. 



Treub's investigations * into the structure of the pro- 

 thallus, and the development of the young plant in the genus 

 Lycopodium have brought the close resemblance that may 

 exist between the sporophyte and the prothallus of a 

 Vascular Cryptogam into prominence. It is, however, a 

 difficult question to determine how far morphological im- 

 portance can be attached to the fact. 



The work of Bower 2 on the normal development of 

 Vascular Cryptogams, and especially of their spore-produc- 

 ing members has given considerable support to the anti- 

 thetic theory, by showing that the structural facts in connec- 

 tion with the more recent modifications of these plants 

 would bear the interpretation which that theory assumes. 

 Omitting for the present the consideration of the theoretical 

 views to which these investigations have led, the chief fact 

 bearing on the question we are considering is that sterilisa- 

 tion of potentially spore-producing tissue has been shown to 

 occur in the sporogonia of Bryophyta and in the sporangia of 

 Vascular Cryptogams and Angiosperms. The complicated 

 spore-producing structures seen in some of the latter groups 

 may be viewed as having been derived from simpler 

 sporangia in essentially the same way as the antithetic 

 theory assumes the first stages of development of the 

 sporophyte to have taken place. This view, originally 

 suggested by Celakovsky, has been elaborated by Bower, 

 and makes it possible to understand how the passage may 

 have occurred from the wholly dependent Bryophyte sporo- 

 gonium to the plant in the Vascular Cryptogams which is 

 only at first dependent on the gametophyte. This com- 

 parison has been facilitated by fuller knowledge of the 

 structure of the simpler sporophytes of the latter group 

 especially that of Phylloglossum; the full life history of 

 which is unfortunately not yet known. 



iTreubO). -Bower (13). * Ibid. {2). 



