PHYLOGENY OP CHYTRIDIALES AND VEGETATIVELY SIMILAR FORMS 633 



SAPROLEGNIACEAE 



ments from holocarpic to eucarpic monocentric forms and finally to 

 eucarpic polycentric forms. So far as known the Hyphochytriales have 

 not given rise to further advanced, hyphal forms of a truly mycelial 

 nature. The Chytridiales, on the contrary, are certainly closely related to 

 the Blastocladiales and Monoblepharidales, culminating in the latter in 

 an oosporic mode of sexual reproduction. This line seems to end blindly. 

 From the Lagenidiales we can draw lines of ascent to the Saprolegniales 

 and Peronosporales. 



PERONOSPORACEAE 



ALBUGINACEAE 



ENTOMOPHTHORALES 



I 

 PYTHIACEAE MUCORALES 



i 



LEPTOMITACEAE 



LAGENIDIACEAE 



I 

 OLPIDIOPSIDAGEAE / VAUCHERIACEAE 



HIGHER /si PHONALES 



Fig. 205. Suggested lines of evolution of 

 the biflagellate Phycomyceteae, based upon 

 Sachs's and Mez's idea of the origin of the 

 Saprolegniales from the Siphonales. (After 

 Bessey: Mycologia, 34(4):355-379.) 



On the contrary Mez (1929), de Bary (1884), and many others have 

 suggested that the evolution may have been regressive from the Sapro- 

 legniales or from the Pythiaceae, to the Lagenidiales, by a process of 

 simplification. From the simple, holocarpic Olpidiopsidaceae, by the loss 

 of the posterior or anterior flagellum could have arisen the Hyphochy- 

 triales and Chytridiales respectively. No forms are known from which the 

 Monoblepharidales and Blastocladiales might have arisen and then by 

 regression led to the production of the Chytridiales. The Saprolegniales 

 are assumed by Mez and by Sachs (1874) under this hypothesis to have 

 arisen by loss of chlorophyll from some alga similar to Vaucheria in the 

 Siphonales, at a point in the evolution of this alga prior to the substitution 

 of a single compound zoospore for the many separate biflagellate zoo- 



