ORDER SAPROLEGNIALES 



109 



Fig. 34. Saprolegniales, Family Saprolegniaceae. Thraustotheca prirnoachlya Coker 

 & Couch. (A) r/ira«sto</iemtypeof zoosporangium. (B) ^c/i/ya type of zoosporangium. 

 (C) Oogone and antherid. (D) Oospore germinating and producing several small 

 zoosporangia. (Courtesy, Coker and Couch: J. Elisha Mitchell Sci. Soc, 40(3-4): 

 197-202.) 



tube which produces a new mycelium. In Thraustotheca prirnoachlya 

 Coker & Couch the germinating oospore may divide into several internal 

 spores or these may be formed in short germ tubes growing out through 

 the pits of the oogone wall (Coker and Couch, 1924). Ziegler (1948) 

 studied the germination of 26 species of this family representing 6 genera 

 and found the following 4 types. (1) "A long or short germ tube is formed, 

 with an apical sporangium"; (2) "the germ tube produces a sparsely 

 branched mycelium with a sporangium at the apex of the main hypha or 

 a branch"; (3) "the primary germ tube forms a branched mycelium"; 

 (4) "the primary germ tube forms a long unbranched hypha." (Fig. 34 D.) 



Apparently the primitive form of zoospore in this family is pear- 

 shaped with two equal anterior flagella. Only such primary zoospores are 

 formed in the two known species of Pythiopsis. Far more often the species 

 of this order are dimorphic. Other forms show various modifications of 

 the dimorphic plan. 



The zoosporangia are typically terminal segments of hyphae, but 

 sometimes several are formed one behind the other. When the zoospores 

 are discharged a new zoosporangium may arise by proliferation, some- 

 times five or six times. In other cases the new zoosporangia are formed 

 on short or long sympodially produced branches. Usually they are slender, 

 like the supporting hypha, or clavate or ovoid. Under certain cultural 

 conditions the hypha may form ovoid or clavate zoosporangia in chains, 

 each opening by an exit pore near its apical end. Under some conditions 



