BLASTOCLADIALES 619 



in male and female gametangia in equal number, there appears to be here a 

 peculiar type of differentiation in which the distribution of chondriosomes is 

 of primary importance in the determination of sex. 



7. In the visible expression of sexual differences there is a definite quanti- 

 tative factor in the amount of chondriosomes (nuclear cap) and a qualitative 

 factor in the colour of the lipoid granules. 



8. The extranuclear nature of the nuclear cap found in the gametes and 

 zoospores of A. arbuscula is demonstrated and its chondriosomal origin de- 

 scribed. 



Ritchie (1947), as well as Wilson (1952), disagrees with Hatch's views 

 concerning the mitochondrial origin and the composition of the nuclear 

 cap (see above). ' 



On the asexual plant the thin-walled zoosporangia form uninucleate 

 zoospores which are liberated through several pores. The development 

 and cytology were studied first by Barrett (1912a) and then by McCranie 

 (in Sparrow, 1943), (Figs. 41 A-F, p. 622; 42 L, p. 626) and, more 

 recently, by Ritchie (1947). The latter investigated the formation and 

 structure of the zoospores of Allomyces arbuscula, A. javanicus, and A. 

 anomalus. 



According to Ritchie, in living material a hyphal tip swells and is 

 soon cut off by a septum. After the sporangium attains mature size, 

 spore origins appear. These at first are never distinct and they soon 

 fade out completely. A period ensues in which nothing is visible in the 

 cytoplasm but the lipoid droplets outlining the positions of the nuclei. 

 This phase may last several days and is terminated by the reappearance 

 of the spore origins. The nuclei then move to the surface and the lipoid 

 droplets collect between them. Fissures cleave out uninucleate polyhed- 

 ral blocks of protoplasm and within a minute or two nuclear caps 

 develop. The exit papillae (one to six) become distended and when the 

 spores are completely delimited one and then others open. The first 

 spores to emerge remain massed for a few moments before dispersal; 

 the later ones, after a period of amoeboid movement, swim off individ- 

 ually. It was noted by Ritchie that when maximum size is attained, 

 the sporangium decreases suddenly and sharply in volume. A second, 

 even sharper, shrinkage takes place just prior to spore release. 



1 See Turian and Kellenberger (1956) who believe ribonucleic acid is concerned 

 in its composition. 



