ORDER BLASTOCLADIALES 



85 



Fig. 25. Blastocladiales, Family Blastocladiaceae. Allomyces arbusculus Butler. Life 

 cycle. (After Emerson. Courtesy, Sparrow: Aquatic Phycomycetes, Exclusive of the 

 Saprolegniaceae and Pythium, Ann Arbor, Univ. Michigan Press.) 



same stage of development. Those from the thick-walled resting sporangia 

 behave differently according to the species. In the main the reproduction 

 is of two distinct types. In the section Euallomyces, represented typically 

 by A . javanicus Kniep and A . arbusculus Butler, the zoospores from the 

 thick-walled resting spores produce gametophytes of approximately the 

 same structure as the sporophytes described above. In place of the 

 sporangia, chains of gametangia are produced terminally on the branches. 

 There are usually two, rarely more, in each chain. These consist of a 

 smaller and a larger gametangium, the former being terminal in A. java- 

 nicus, the latter terminal in A. arbusculus. The smaller, male gametangium 

 is salmon-pink to orange in color, the larger, female gametangium is 

 colorless. The gametes emerge from one to three exit papillae. The male 

 gametes are smaller and faintly colored and about twice as numerous as 

 the colorless female gametes. They fuse promptly and the biflagellate 

 zygote germinates almost at once to produce the sporophyte. This type 

 of sexual reproduction and alternation of generations in this genus was 

 first reported by Kniep (1929, 1930) in A. javanicus. Hatch (1933) demon- 

 strated it in A. arbusculus. Since then Hatch (1935, 1938), Emerson 

 (1941), McCranie (1942), and Wolf (1941) have given the genus intensive 



