CHAPTER V 

 CLASS ARCHIMYCETES 



According to a proposal in a letter from E. Fischer, the fungi here 

 called Archimycetes are the earlier Myxochytridiales. They include 

 naked, often amoeboid forms which develop holocarpic reproductive 

 organs by division of the whole thallus. They stand very close to the 

 Myxomycetes and flagellates and chiefly differ from them in their 

 parasitism. 



They are divided into four families: the Olpidiaceae and Synchyt- 

 riaceae, whose zoospores are oval or pyriform with trailing flagella; 

 the Plasmodiophoraceae, whose zoospores are amoeboid, with an apical 

 flagellum ; and the Woroninaceae whose zoospores are reniform with two 

 lateral flagella. The thallus forms a single sporangium in the Olpidia- 

 ceae, a sporangiosorus in the Synchytriaceae and a multitude of spores 

 or spore balls in the Plasmodiophoraceae. 



At present the relationships of these four families are still obscure. 

 The Plasmodiophoraceae and Woroninaceae, are peculiar on account of 

 their schizogonia; it is questionable, however, whether the formation 

 of sori in the Synchytriaceae may not be an extreme reduction of schizo- 

 gonia, if the nuclear divisions up to the formation of the protospores and 

 their analogues are called the vegetative phase and the subsequent ones, 

 which lead to zoospore formation, the reproductive phase. Previous 

 studies, however, have given no basis for such considerations. Further, 

 the zoospores of the Olpidiaceae and Woroninaceae, like the swarm spores 

 of many Monadineae, before germination on the host are always sur- 

 rounded by a membrane, and discharge their contents into the host cell 

 leaving their empty membrane on its surface. The zoospore of the 

 Synchytriaceae and possibly of the Plasmodiophoraceae withdraws its 

 flagellum and then as a whole penetrates the host plant. How far this 

 lack of a membrane may be evaluated phylogenetically is not yet clear. 



These four families are regarded as four different lines which have 

 developed independently of each other from the Sporozoa-Flagellate- 

 Myxomycete line. Since in the Woroninaceae and Plasmodiophoraceae, 

 the distinguishing points have not yet been determined cytologically, 

 a discussion of these relationships would be premature. 



Olpidiaceae. — This family is very simply organized and, as far as 

 known, reproduction proceeds isogamously by aplanogametes. 



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