84 PHYCOMYCETEAE 



In B. cystogena Couch and Whiffen the thin-walled zoosporangia are 

 wanting. The zoospores from the resting sporangia encyst almost immedi- 

 ately and soon produce four smaller gametes each, also posteriorly 

 uniflagellate, which fuse in pairs and germinate at once to produce the 

 original stage. When cultured on an agar medium, several other species 

 besides B. siuhenii are spherical, with rhizoids on all sides, but on other 

 media clavate or cylindrical with a septum setting off the sporangium or 

 gametangium. (Fig. 24A-E.) 



Blastodadia. This genus is more complicated in its structure. The 

 basal segment, bearing at its base tapering branched rhizoids, may be 

 spherical (in B. glohosa Kanouse) and bear on its surface the cylindrical 

 zoosporangia and subspherical or ovoid resting sporangia, sometimes 

 interspersed with slender threads. On the other hand, it may be cylindrical 

 and branched into more or less dichotomously dividing cylindrical hyphae 

 which bear the sporangia of both types. Often the hyphae bear a spo- 

 rangium apically and then branch sympodially so that the successive 

 sporangia appear racemose in arrangement. Slender setae may also be 

 present. The commonest species is apparently B. pringsheimii Reinsch, 

 which varies from a large clavate structure bearing the zoosporangia and 

 resting spores and setae at its apex or which may branch as described 

 above. In what was apparently this species the author (1939) observed 

 the union of equal swarm cells whose subsequent fate could not be fol- 

 lowed and whose origin, whether from thin-walled zoosporangia or thick- 

 walled resting sporangia was not ascertained. Miss Blackwell (1940) 

 studying apparently the same species very intensively was unable to 

 confirm this observation. (Fig. 24F, G.) 



Allomyces. About six species are recognized in this genus. They are 

 distinguished mainly by their reproductive structures and life cycles. 

 Vegetatively they consist of a basal cylindrical segment attached by 

 tapering branched rhizoids to the substratum, and branching dichoto- 

 mously or sympodially into gradually more slender hyphae, sometimes 

 forming a tangled mycelial mass. The branches are blunt at the tip and 

 show here and there the pseudosepta characteristic of the genus, there 

 often being a constriction at each pseudoseptum. These are sometimes 

 wheel-Uke in appearance with radiating rods separating a circle of more 

 or less triangular openings. At the ends of the branches, singly or some- 

 times in chains, are produced the cylindrical or somewhat oval, thin- 

 walled zoosporangia. By sympodial branching these may come to have 

 the appearance of a racemose arrangement. The zoospores escape by one 

 or several inoperculate openings. The same plants may also bear the 

 thick-walled resting sporangia which vary in shape from spherical to 

 ovoid or even lemon-shaped and with the brown outer wall deeply 

 punctate. The zoospores from the thin-walled zoosporangia produce the 



