INTRODUCTION 5 



ent monad ancestors, the first from a uniflagellate type, the second 

 from a biflagellate, and to have undergone independent development. 

 Other features are correlated with the flagellation of the zoospore. 

 Within the "Saprolegniineen-Peronosporineen" series two subseries are 

 distinguished, the "Saprolegniineae" and "Pythium-Peronosporineae," 

 which have probably arisen from an archetype similar to Ectrogella. 

 Although the Monoblepharidales are recognized as distinct in origin 

 and development from both of these series, and are probably related 

 to the Blastocladiales, their ancestry is in doubt. For further details 

 and for specific evidence refuting the theories of algal origin of the 

 chytrids, or their origin from higher fungi, the reader is referred to 

 the paper cited above. The present author is thoroughly in accord with 

 the main features of Scherffefs ideas on phylogeny, since they seem 

 best to fit the facts as now known. It can be added, however, that, as 

 a result of discoveries subsequent to the publication of Scherffefs 

 work, the Monoblepharidales appear to be unquestionably related to 

 the chytrids and might be thought of as a terminal group of the "Chyt- 

 ridineen" series. As Scherffel intimated, the Blastocladiales show un- 

 doubted relationships to the chytrids on the one hand, and to the 

 Monoblepharidales on the other. 



It is believed that the interpretation of the Chytridiales given here, 

 a modification of Scherffers, has resulted in the recognition of a com- 

 pact interrelated group of organisms. Elimination from it of numerous 

 fungi with similar thallus structure but with very different reproductive 

 bodies (for example, the Hyphochytriales, the Olpidiopsidaceae, and 

 so on) has not only made the group a more homogeneous natural one 

 but has also reestablished it in its original sense (Sparrow, 1935b). 

 The transference of the simple biflagellate chytrid-like fungi to orders 

 with which they appear to have greater affinities than with the Chytri- 

 diales, has brought about a more natural arrangement of all the lower 

 Phycomycetes. Although the classification would appear to rest pri- 

 marily on the flagellation of the zoospore, other characters correlated 

 with this are found in the great majority of species, as Scherffel (1925a) 

 pointed out. In the chytrid series the frequently radially symmetrical 

 zoospore is posteriorly uniflagellate; its plasma is homogeneous, almost 

 or completely free of granules, and bears a single conspicuous, often 



