102 PHYCOMYCETEAE 



tode. The nucleus divides into several nuclei and then an exit tube is 

 formed, but the actual production of the zoospores was not observed. 



The members of this family are parasitic, rarely saprophytic, in cells 

 of algae (mostly fresh-water species), microscopic animals, or their eggs, 

 and in the case of Lagena, parasitic in the roots of grasses. Sometimes a 

 small individual is nonseptate and is scarcely to be distinguished from 

 one of the Olpidiopsidaceae while in Lagenidimn giganteum Couch the 

 fungus body is elongated, multiseptate, and quite mycelium-like and up 

 to 40 fj. thick in extreme cases. It is in cases like this that the supposition 

 is strengthened that this family represents a reduction in size and com- 

 plexity from higher, better developed fungi, perhaps close to Pythium. 

 The three genera recognized by Karling and by Sparrow are Lagenidium, 

 with 15-20 species, Myzocytium, with 4 or 5 species, and Lagena with one 

 species. 



In the genus Lagenidium the coenocytic segments may be few in 

 number and all included within one cell of the algal host or they may 

 pierce the cell walls of the latter to continue through several cells. In 

 L. giganteum the hosts are small aquatic Crustacea and larvae of mos- 

 quitoes. Not only does the extensive coarse mycelium fill the host but it 

 extends out into the surrounding water up to a distance of 0.1 mm. This 

 species has been brought into pure culture by Couch. Its sexual stage is 

 unknown. In those species where sexual reproduction has been observed 

 the female gametangium usually enlarges considerably as the oospore 

 develops. The antherid is an unmodified or only slightly modified vegeta- 

 tive cell, either adjacent to the oogone in the same filament or in an 

 adjacent filament. In the latter case this may indicate heterothallism. 

 Lagena (Vanterpool and Ledingham, 1930) is a parasite in the roots of 

 wheat {Triticum aestivum L.) and other grasses, which are weakened by 

 the presence of this fungus. The organism may be much elongated or 

 even more or less coiled in the host cell but not septate. It produces a 

 single exit tube through which the contents of the zoosporangium emerge 

 into a vesicle in which they undergo their final transformation and swim 

 away after rupturing its membrane. Ne,ar-by thalli may unite by a 

 conjugation tube through which the contents of one cell pass into the 

 other, rounding up there to form a thick-walled oospore. The mode of 

 germination of the latter is unknown. (Figs. 32, 33.) 



Possibly belonging to this family is Aphanomycopsis (Scherffel, 1925) 

 forming a more or less elongated and coiled, often somewhat branched, 

 coenocytic thallus in the cell of a Diatom. This thallus is transformed into 

 a zoosporangium with one or more exit tubes at whose mouths the primary 

 (nonflagellatc) zoospores encyst, later emerging and swimming away as 

 zoospores of the secondary type. Sexual reproduction has not been 

 demonstrated although thick-walled resting spores are formed in enlarged 



