858 AQUATIC PHYCOMYCETES 



with the exception of the large oil droplet, which persists. The oospore 

 enlarges and cracks open the surrounding oogonial wall. One or 

 two somewhat irregular thick germ tubes protrude through the wall of 

 the oospore. These tubes elongate, become constricted at intervals, and 

 eventually establish the new mycelium. A plug is formed in the first 

 constriction which prevents the backflow of materials into the now 

 empty oospore. Frequently the oospore after cracking open the oogo- 

 nial wall slips out of its container and falls to the bottom of the culture 

 dish. 



In Apodachlyella completa, Humphrey (1893) and Indoh (1939) have 

 shown that the sex organs are of a most peculiar type (Fig. 69 F, p. 875). 

 The contents of the oogonium divide into from two to twelve (usually 

 from four to seven) oospheres, which eventually become oospores. The 

 suboogonial segment gives rise to from one to three branches, which are 

 constricted and segmented like the ordinary vegetative hyphae. The 

 terminal segment functions as the antheridium and is applied laterally 

 to the wall of the oogonium. The contents then fragment into from four 

 to ten small spheres, each of which produces a short germ tube and 

 simulates a germinating zoospore. According to Indoh, these tubes 

 penetrate the antheridial and oogonial walls and accomplish fertiliza- 

 tion. It is not clear whether all the antheridial spheres discharge their 

 contents into the oogonium. Indoh's observations on this extraordinary 

 phenomenon closely follow those of Humphrey. The latter noted, 

 however, that although the tubes usually grew toward the oogonium 

 there were occasional exceptions, which appear from Indoh's figures 

 to have been present in his material also. These exceptions, together 

 with the occurrence of a few empty terminal segments devoid of such 

 cysts and tubes, led Humphrey to suspect that his material was parasi- 

 tized. 



The sex organs of the Rhipidiaceae are in several ways more highly 

 specialized than those of the Leptomitaceae. The oogonium always 

 bears a single egg, the contents of which during maturation are strongly 

 differentiated into a large somewhat dense mass of ooplasm and a thin 

 vacuolated peripheral layer of periplasm. A single well-defined anther- 

 idium is formed which is usually fairly constant as to its point of appli- 

 cation to the oogonial wall and which always produces a conspicuous 



