114 



PHYCOMYCETEAE 



Fig. 37. Saprolegniales, Family Saprolegniaceae. Leptolegnia caudata de Bary. (A) 

 Young oogone and two antherids. (B) Same structures five hours later, one antherid 

 discharging contents into oogone. (C) Same structure two and a half days later, 

 oospore wall considerably thickened. (D) Stained section showing entry of sperm 

 nucleus into the egg, with remains of peripheral supernumerary nuclei in both oogone 

 and antherid. (Courtesy, Couch: Am. J. Botany, 19(7) -.584-599.) 



victims. Plectospira (Drechsler, 1927, 1929) is parasitic in plant roots and 

 resembles Aphanomyces except for the production of lobulate masses of 

 hyphae which apparently serve as auxiliary storage parts of the zoospo- 

 rangia, much as occurs in some species of the genus Pythium (see p. 127). 

 The oogones have a single egg but no periplasm and become surrounded 

 by many antherids, up to over 50, of which only a few reach full develop- 

 ment. Leptolegnia resembles Aphanomyces in its slender hyphae and its 

 slender zoosporangium with a single row of zoospores, as well as in the 

 production of only a single egg in the oogone. It differs in that the primary , 

 zoospores swim away immediately and encyst at a distance as inj 

 Saprolegnia. (Figs. 36, 37.) 



Dictyuchus resembles Achlya and like it produces clavate or cylindricj 

 zoosporangia which may be single or in chains or more or less sympodially 

 clustered. They may separate from the supporting hyphae and float 



