BLASTOCLADIALES 615 



but as growth proceeds, secondary ones, male and female, are alternately 

 formed on sympodial branches or in basipetal succession. The game- 

 tangia produce and liberate their gametes in the same manner as do the 

 zoosporangia. During gametogenesis, however, the changes which occur 

 in the aspect of the cytoplasm differ from those found in the zoospo- 

 rangia. ] Hatch (1935) states that in Allomyces arbuscula the dense cyto- 

 plasm of the contents of the hyphal tip which will give rise to game- 

 tangia is gray black, and that this color persists until after the septa de- 

 limiting the terminal female and subterminal male gametangia are laid 

 down. The lateral walls of the maturing structures then distend and the 

 color of the male gametangium grows lighter, at first becoming yellow- 

 ish and later assuming a rusty hue. The female becomes dull gray. With 

 the appearance of the papillae of discharge the contents of the male 

 gametangium turn salmon-pink, whereas those of the female remain 

 unchanged. In both A. arbuscula and A. javanicus the larger, female, 

 gametes are colorless and resemble zoospores. The male, however, is 

 small, more active than the female, and, so far as is known, always 

 pigmented. Its contents vary with age from faint orange to brick-red, 

 depending on the amount of coloring matter accumulated (Emerson, 

 1941). The pigment was determined by Emerson and Fox (1940) to be 

 composed of gamma-carotene, a relatively rare isomere of carotene. 

 It is located in minute lipoid granules, which in the early stages of 

 development of the gametes are dispersed throughout the cytoplasm 

 of the gametangium. At maturity the colored material becomes more 

 or less localized in the gametes but is never in single globules as in the 

 zoospores of such an aquatic chytrid as Rhizochsmauum aurantiacum. 

 Emerson and Fox (1940) pointed out the relationship of carotene to 

 reproduction in both algae and higher plants and suggest that "such 

 compounds may play important biochemical roles in sexuality and the 

 processes involved in the metabolism of reproduction." 



Chance alone seems to decide whether or not male and female 

 gametes, once discharged, will meet and fuse. There is no evidence to 

 indicate that gametes from the same thalli are incapable of doing so. 

 In fact, Emerson and Wilson (1954) reveal that fusion between gameies 

 of the same species of plant is immediate, whereas that between gametes 



1 See Turian's important paper on this process in Bull. Soc. hot. suisse, 67 : 458. 1 457. 



