ORDER CHYTRIDIALES 45 



in fungi; in the eggs or larvae of worms, Arthropoda, or simpler animals; 

 or, perhaps more often, saprophytic in dead plant or animal material. 

 They are abundant in some types of soils and in fresh and salt water. 

 Their life histories are poorly known in many cases but have been worked 

 out very well in some species. In general the life history is as follows : The 

 posteriorly uniflagellate zoospore after a period of swimming settles down 

 on the substratum and penetrates it or encysts on the outside and then 

 enters it wholly or merely as a more or less extensive haustorium or 

 system of rhizoids. Unlike the Mycetozoa it produces a cell wall of its 

 own, usually at an early stage. The single nucleus divides repeatedly as 

 the cell enlarges, and eventually the cytoplasm fragments into very many 

 uninucleate zoospores or naked gametes or into uninucleate cells which 

 produce cell walls and sooner or later divide internally into zoospores or 

 naked gametes. Sexual reproduction where known may be accomplished 

 by the union of two motile gametes before entry into the substratum, 

 by the union of two cells attached to or residing within the substratum, 

 or by the union of two cells by means of a rhizoid through which a gamete 

 nucleus passes. 



In this order the zoospores or motile gametes escape through an exit 

 papilla or tube whose apex softens and permits the motile cells to push 

 out (the inoperculate series), or they escape through a sort of cap that 

 opens like a trap door, the so-called operculum (the operculate series). 

 This operculum is more generally at the apex of the papilla or tube, but in 

 Karlingia (Johanson, 1944) and Catenomyces (Hanson, 1945) it may be 

 formed within the tube some distance from the apex, which softens and 

 deliquesces much as in the inoperculate forms. The single posterior 

 flagellum is of the "whiplash" type, i.e., the basal portion consists of a 

 firmer outer tube whose more fluid contents extend beyond its tip as a 

 more slender, very flexible structure resembling the lash of an old- 

 fashioned buggy whip. This lash is sometimes very short or scarcely 

 distinguishable. 



The cell wall of the Chytridiales does not ordinarily give the charac- 

 teristic blue or violet coloration of cellulose when chloriodide of zinc is 

 applied, but there are a number of exceptions in which this reaction is 

 distinct. Whether chitin is actually present in all cell walls that do not 

 show the cellulose reaction is not certain. Harder (1937) reported that in 

 one species of the Family Rhizidiaceae different individuals possess 

 cellulose or chitin, perhaps in cells of different ages. Nabel (1939) demon- 

 strated the presence of chitin but not of cellulose in some species of 

 Rozella and Synchytriuni. Schwartz and Cook (1928) report the presence 

 of cellulose in the cell walls of Olpidium radicale while Scherffel (1925) 

 states that in certain structures of Micromycopsis cristata Scherffel and 

 Synchytrium mercurialis (Lib.) Fuckel cellulose is present, Tischler (1927) 



