670 AQUATIC PHYCOMYCETES 



branched strongly tapering rhizoids; asexual plant bearing terminally, 

 sympodially, or in basipetal succession thin-walled zoosporangia which 

 discharge their fully formed posteriorly uniflagellate zoospores through 

 one or more pores produced upon the deliquescence of prominent 

 papillae, and persistent or deciduous resting spores with a thick brown 

 punctate outer wall and a thin inner one, the resting spores upon 

 germination producing either (a) posteriorly uniflagellate planonts which 

 give rise directly to new asexual plants or to sexual plants, or (b) 

 posteriorly flagellate planonts which immediately encyst, each of the 

 cysts forming endogenously four isogamous uniflagellate gametes which, 

 after emerging from the cyst through a pore, fuse in pairs, the zygote 

 germinating to form asexual plants; sexual plant similar to the sporo- 

 phyte, monoecious, bearing male and female gametangia terminally in 

 pairs or alternating in basipetal succession, gametes anisogamous, 

 posteriorly uniflagellate, the small male always pigmented, the larger 

 female colorless, the planozygote posteriorly biflagellate and germinat- 

 ing to form the asexual plant. 



In water and soil on plant and animal remains. 



Emerson (1938a, 1941) established three subgenera, based on the 

 type of life cycle exhibited. His groupings have been adopted here (but 

 not as subgenera). They are more fully discussed under "Life Cycles" 

 (see pp. 624-627). 



KEY TO THE SPECIES OF ALLOMYCES 



Life cycle of the Euallomyces type; pits on resting spore closely spaced 

 Gametangia when first formed developing in pairs, with the female 



terminal A. arbuscula, p. 671 



Gametangia when first formed developing in pairs, with the male 

 usually terminal 

 Primary male gametangia sometimes hypogynous; female game- 



tangium slightly longer than male A. x javanicus, l p. 673 



Primary male gametangia always terminal; female gametangium 



two to four times longer than male A. macrogynus, p. 674 



Life cycle of the Cystogenes type; pits on resting spore widely spaced 

 Resting spores mostly beaked or fusiform, cytoplasm often pigment- 

 ed A. moniliformis, p. 676 



1 Natural hybrid between A. arbuscula and A. macrogynus. 



