342 A TEXTBOOK OF THEORETICAL BOTANY 



by some Fungi, and this is essentially characteristic of plants, being very 

 rare among animals. The cell walls of some Fungi do, however, contain 

 chitin, which is again of animal nature. 



If it is true that the Fungi have had an independent origin we must assume 

 that all the types existing at the present time have been evolved from those 

 primitive ancestral forms. We cannot consider this view in detail, but it is 

 sufficient to say that no difficulty exists in tracing the main lines of such an 

 evolution from the very simplest known Fungi to the more complex Phyco- 

 mycetes such as Mwror or Saprolegnia. It is, moreover, quite possible to suggest 

 ways in which the Ascomycetes may have arisen from a Phycomycete origin. 

 In the opinion of those who support this view the similarity between the 

 sexual apparatus of the Ascomycetes and the Red Algae is due to convergence, 

 or the production of similar structures in response to similar environmental 

 circumstances and requirements, rather than to any phylogenetic connection. 



The Basidiomycetes stand apart in this consideration. Among all the 

 forms known at the present day there is none which offers us any clue as to 

 their origin. They show little or no connection with the Ascomycetes and 

 comparatively little with the Phycomycetes. On the other hand, there is no 

 group of Algae which can be pointed out as their possible ancestors. The 

 fossil record tells us that in the course of geological time many families and 

 even whole groups of organisms have died out, and it would seem that the 

 types which gave rise to the Basidiomycetes may have completely disappeared. 

 Whether they were Fungi or Algae it is fruitless to speculate. 



