92 AQUATIC PHYCOMYCETES 



the rhizoids (Fig. 6 L-M, p. 88). The vegetative system, therefore, 

 is at all stages in its development devoid of nuclei. Progressive cleavage 

 of the contents of the rudiment into zoospores is initiated soon after 

 the protoplasm has become finely granular and homogeneous. The 

 cleavage furrows extend centripetally from the periphery of the con- 

 tents as well as centrifugally from clefts originating in the mid-region. 

 Apparently there is no central vacuole. The conspicuous nuclear cap 

 of the zoospore appears some time after the initial stages of cleavage. 

 There is evidence to show that it is wholly of chondriosomal origin. 

 No details of the formation of the flagella or operculum have, presum- 

 ably, been observed in fixed and stained material. 



The resting spore is asexually formed on a thallus similar to that 

 which produces the zoosporangium. The single nucleus (occasionally 

 two) lies in the enlarged rudiment and is surrounded by small heavily 

 staining granules similar to those in the resting spores of Polyphagia 

 euglenae and Cladochytrium replication. The wall of the mature resting 

 spore consists of an outer thick layer, a thinner middle layer (meso- 

 spore), and an innermost thin membranous endospore. The outer wall 

 may occasionally be smooth, but typically it is strongly roughened. 

 During its formation a broad envelope of hyaline gelatinous material 

 of unknown origin surrounds the whole spore. This material shrinks 

 during maturation and becomes transformed at first into broad warts 

 and eventually into lobed processes. Whether these lobes are the result 

 of the infolding of the hyaline material or of outgrowths from the resting 

 spore into the hyaline zone is not known. The wall material, which 

 in the course of its development gave a negative reaction for cellu- 

 lose, becomes yellowish and opaque. At germination the resting spore 

 functions as a prosporangium. Division of the nucleus, which is mi- 

 totic, appears to occur only in the zoosporangium. This structure in 

 most instances rests directly on the empty case of the resting spore, 

 although occasionally it may be produced at the tip of a long tube. 



Among the newer cytological observations published, those of Anti- 

 kajian (1949) on the inoperculate monocentric chytrid Asterophlyctis 

 sarcoptoides (p. 434), a rhizidiaceous form living in insect exuviae, are 

 the most complete. She reports that the young apophysate thallus is 

 uninucleate (Fig. 7 A-B, p. 94), and that the nucleus increases in size 



