G32 



THE PHYLOGENY OF THE FUNGI 



motile, anteriorly biflagellate algae (Heterocontae or Xanthophyceae). It 

 is necessary to make the assumption that the loss of chlorophyll and the 

 adoption of a saprophytic or parasitic mode of life occurred early in their 

 evolution. The simpler Lagenidiales represent forms in which both flagella 

 are retained, as well as the cellulose composition of the cell walls. For the 

 Hyphochytriales we must assume a gradual modification of the hetero- 

 contal habit until finally (as sometimes occurs in the algae) the shorter, 

 posteriorly inclined flagellum entirely disappeared, leaving only the single 

 anterior tinsel type flagellum. At the same time the cellulose became in 

 part replaced by or concealed by an admixture of fungus chitin. For the 

 Chytridiales (in the narrower use of the term) the anterior (tinsel type) 

 flagellum has disappeared leaving the single, posteriorly directed whiplash 

 flagellum. Concurrently the cellulose reaction of the cell walls has become 

 less and less marked, appearing only in a minority of the species so far 

 studied. (Fig. 204.) 



These three groups have undergone parallel evolutionary develop- 



ENTOMOPHTHORALES 



MUCORALES 



PERONOSPORACEAE 



MONOBLEPHARIDACEAE 



BLASTOCLADIACEAE 



SAPROLEGNIACEAE 



LEPTOMITACEAE 



ALBUGINACEAE 



PYTHIACEAE 



CLADOCHYTRIACEAE 



RHIZIDIACEAE 



SYNCHYTRIACEAE 



OLPIDIACEAE 



ANTERIOR FLAGELLUM LOST 



LAGENIDIACEAE 



HYPHOGHYTRIACEAE 



POSTERIOR FLAGELLUM LOST 



OLPIDIOPSIDACEAE 



,BOTH FLAGELLA RETAINED 



HETEROCONT UNICELLULAR ALGAE 



Fio. 204. Suggested lines of evolution of the Pliycomyreteae, based upon the idea of 

 their origin from unicellular algae. (After Bcssey: M ycologia, 34(4):355-379.) 



