620 AQUATIC PHYCOMYCETES 



Fixed and stained sections showed that in zoosporogenesis cleavage 

 progresses centrifugally and the spores become delimited before the 

 nuclear caps are deposited. The mitochondria, conspicuous in living 

 hyphae, disappear in the young sporangium. When the nuclear caps 

 are about to form, deep-staining granules appear in the cytoplasm. 

 These, which have been interpreted as mitochondria by some inves- 

 tigators, flow together into larger masses until finally they form a single, 

 crescent-shaped cap attached to the nucleus. 



On the basis of the staining reactions Ritchie indicates that the nu- 

 clear cap cannot be mitochondrial in origin. Furthermore, the cap 

 cannot be dissolved by certain solvents as would probably be true if 

 this were the case. He concludes that it is partly from condensed ma- 

 terial in the cytoplasm and partly from material extruded from the 

 nucleus. Although its eventual fate is undetermined, it has not been 

 seen to break up into mitochondria. 



Unusual features of zoospore structure and behavior were noted by 

 Teter (1944) in Sparrow's strain of Allomyces moniliformis from Trin- 

 idad. Teter reported that in this material the zoospores from the spo- 

 rangia were always devoid of flagella. Following a period of amoeboid 

 movement the spores encysted. The cysts either gave rise to new 

 aflagellated zoospores, which crept out and in their turn became quies- 

 cent, or developed rhizoids after which an undersized swarmer emerged. 

 The forming of a second zoospore is a clear case of repeated emergence, 

 the only well-authenticated instance so far recorded for Allomyces. 

 None of the planonts (zoospores or gametes) of the Trinidad strain 

 possessed flagella. Teter carried along parallel cultures under similiar 

 conditions of a consistently flagellated strain of A. moniliformis. The 

 control strain continued to form flagella. Lack of them, therefore, in 

 the Trinidad strain was not due to poor developmental conditions. 



The resting spore in Allomyces, which is generally formed only on 

 the asexual thallus, may at its maturity fall from the plant, still surround- 

 ed by its persistent outer hyphal wall, or this hyphal sheath may burst 

 and the spore drop from it. At germination the contents of the resting 

 structure swell, the outer thick, pitted wall cracks, and the inner thin 

 membrane surrounding the living contents bulges out. This thin-walled 

 protruding sporangium then produces several discharge papillae, which 



