chap, i The Nature of Alternation of Generations 55 



generations of a Thallophyte. This idea of the intercala- 

 tion of the sporophyte as a new and later generation is 

 hinted at in the writings of Braun and was again presented 

 by Bower some years later, though in a different position 

 in the life-cycle. 



From this time onward we can trace a change in the 

 nature of the controversy. It was realized that attention 

 had been paid too exclusively to morphological considera- 

 tions only, and that physiological influences need to be 

 taken into account, while it is of the highest importance 

 to obtain if possible correct views of the descent of the 

 higher plants from the Thallophyta. Two questions were 

 thus forced to the front — What determined the origin of 

 the sporophyte ? and, Has the evolution of the sporophyte 

 of the higher vascular plants passed through a stage corre- 

 sponding to the sporogonium of a Liverwort or Moss ? 



After some years during which controversy was almost 

 hushed, and investigation into structure was resumed in 

 many laboratories, the antithetic theory was strongly sup- 

 ported and amplified in the effort to find answers to these 

 questions. It had gained in the interval many adherents 

 in England and on the continents of Europe and America. 



The position in 1890 was very forcibly expressed by 

 Bower, who stood out prominently as the leading advocate 

 of the antithetic theory, and the man who more than 

 any one since Celakowsky supplied evidence in its favour. 

 It was in this year that he set himself the task of making 

 a careful examination of the spore-producing members of 

 the lower vascular plants with special regard to their 

 development, in the hope that such an investigation might 

 lead to an opinion as to the way in which a transition 

 from the typical Bryophyte sporogonium to a sporophyte 

 of the vascular plant may have taken place, and continued 

 the work up to and beyond the expiration of the century, 

 producing a monumental work, accumulating a mass of 



