HYPHOCHYTRIALES IAS 



The zoospore is somewhat elongate, pyriform or obpyriform, with a 

 single flagellum of the tinsel type attached at the forward, narrower end 

 (see "Zoospore," p. 9). In most species of the order there is a small 

 lateral, more or less refractive body near this same end. Movement is 

 even and deliberate and is punctuated by sudden stops and changes of 

 direction, quite different from the behavior of the zoospore of a true 

 chytrid. 



Resting spores have been reported in some genera. In Anisolpidium, 

 where they are somewhat like sporangia in their early developmental 

 stages, a thickened wall soon forms about the contents which lacks a 

 large reserve globule. 1 In Rhizidiomyces only structures that have been 

 interpreted as encysted sporangia have been found. Zopf (1 894) described 

 Latrostiam comprimens as having very thick-walled resting spores. 

 In Hyphochytrium hydrodictii, according to Valkanov (1929b), they are 

 thick-walled, terminal or intercalary, and function directly as sporangia 

 upon germination. No resting spores have been seen in Canteriomyces 

 or in Rhizidiomycopsis. In no instance, save in the problematic genus 

 Reessia, is there any evidence of sexuality preceding resting-spore 

 formation l . In Reessia, Fisch (1884a) says a fusion of isogamous piano- 

 gametes takes place, after which the zygote enters the host cell and 

 becomes a resting spore. 



Canter (1950b) points out that two series exist within the order, one, in 

 which the zoospores are formed within the sporangium, and another, in 

 which they are developed outside from presumably undifferentiated 

 protoplasm. Because these two methods are completely distinct, they 

 constitute differences of generic significance and are so regarded here. 



SYSTEMATIC ACCOUNT 

 H YPHO CHYTRIA LES 



Microscopic aquatic fungi with a body plan resembling that of the 

 Chytridiales, inoperculate, holocarpic or eucarpic, monocentric or poly- 

 centric, the vegetative system rhizoidal or hypha-like with intercalary 

 swellings; zoospores anteriorly uniflagellate, maturing inside or outside 



1 See Johnson (1957a) where these are shown to be sexually formed by en- 

 dobiotic isoaplanogametes fusing in pairs. 



