PHYCOMYCETEAE: CHYTRIDIALES AND 

 HYPHOCHYTRIALES 



THE first class of true fungi, for the Mycetozoa discussed in Chapter 2 

 are not considered to be fungi or even plants, is that of the Phyco- 

 myceteae. In this class the fungus body may consist of 



1. One cell — with a cell wall and with or without non-nucleate 

 rhizoids — which either becomes directly a zoosporangium or gametangium 

 or else empties its contents into an external zoosporangium or 

 gametangium. 



2. Instead of a single cell with non-nucleate rhizoids, nuclei may pass 

 from the first cell through modified rhizoids and take their positions in 

 swellings in the latter, there forming secondary centers. Such fungi are 

 polycentric in contrast to the monocentric forms with but a single cell. 

 When the fungus is entirely contained in the cell of its host and com- 

 pletely lacks rhizoids or haustoria, it is called holocarpic; when it is 

 external to its substratum, or internal and gains its nourishment by 

 means of rhizoids or haustoria, it is called eucarpic. 



3. A still further advance is the development of a true coenocytic 

 mycelium containing many nuclei, usually with rhizoids or nucleate 

 trophic hyphae within the substratum. In general this type of mycelium 

 is not provided with true septa (although greatly perforate pseudosepta 

 occur in Allomyces) except to fence off sporangia and gametangia, injured 

 regions, or portions of the mycelium that have exhausted their proto- 

 plasmic contents. 



In seven of the twelve orders treated here as belonging to the Phyco- 

 myceteae asexual reproduction and, to a much lesser degree, sexual repro- 

 duction is by means of planocytes — i.e., flagellate, naked cells. These are 

 of three types which appear to characterize three series of orders. The 

 types are as follows: flagellum single, posterior; flagellum single, anterior; 

 flagella two, anterior or lateral. In the other five orders (the relationship 

 of two of which is greatly in doubt), asexual reproduction is by means of 



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