58 COMPARATIVE MORPHOLOGY OF FUNGI 



Blastocladiaceae. — In the differentiation of the thallus into principal 

 and secondary axes, this family is reminiscent of the Leptomitaceae, 

 from which it differs by its typical uniflagellate zoospores. As sexual 

 organs are unknown, its systematic position and classification are still 

 obscure. 



In Gonapodya siliquiformis and G. polymorpha, on fruit and twigs 

 lying in water, the mycelium is differentiated into principal and secondary 

 axes (often indefinitely); the individual hyphae are divided by slight 

 constrictions into more or less easily visible segments (Fig. 35, 1). The 

 sporangia are terminal and ovoid and renew by proliferation. They 

 open by an apical pore through which the zoospores pass out singly and 

 swarm or creep away. The systematic position of this genus is doubtful, 

 as zoospores of varied size and flagellar number have been reported in 

 G. polymorpha. 



The other genera, also saprophytic and aquatic, are characterized by 

 the differentiation of its thallus into a highly developed basal cell attached 

 to the substrate by rhizoids and into true hyphae growing from the basal 

 cell and generally ending in sporangia (Fig. 35, 2). The basal cell 

 corresponds essentially to the turbinate cells of the Cladochytriaceae ; 

 it arises from the body of a germinating zoospore while its germ tube 

 develops to a rhizoid system. The sporangia are mostly solitary and 

 terminal, in Allomyces also occasionally moniliform. Their content 

 is split directly into single zoospore initials as in Monoblepharis, i.e., 

 without the formation of a large central vacuole. Germination of most 

 species takes place slowly in the form of a sac out of which the zoospores 

 swarm. They generally creep around like amoebae. The number of 

 their flagella varies from one to three, but in typical cases is one. 



In Allomyces arbuscula (Blastocladia strangulata) the zoosporangial 

 branches still have constrictions as in Gonapodya (Butler, 1911; Barrett, 

 1912; Kanouse, 1927). In these constrictions several broad trabeculae, 

 which permit a free circulation of cytoplasm are formed centripetally 

 from the wall, chiefly in age and upon damage to the hyphae fuse into 

 a false septum. The sporangia are ovoid with several emission collars. 

 In forma dichotoma (Septocladia dichotoma) the constrictions are absent 

 (Coker and Grant, 1922; Kanouse, 1927). 



In Mindeniella spinospora (Kanouse, 1927) the sporangia and oogonia 

 are pedicellate and the oogonial walls echinulate. 



In Blastocladia, the false septa of trabeculae are absent and the sporan- 

 gia are cylindrical with one emission collar. In B. prolifera, the sporangia 

 proliferate as in Saprolegnia. The basal cell in B. ramosa, B. gracilis 

 and B. tenuis is cylindrical and dichotomously branched, in B. globosa 

 is subspherical, in B. rostrata B. Pringsheimii and B. prolifera is variously 

 branched. In B. globosa, antheridial branches have been reported by 

 Kanouse (1927) but the process of fertilization was not observed. Since 



