916 AQUATIC PHYCOMYCETES 



In both the Olpidiopsidaceae and the Lagenidiaceae the resting struc- 

 ture may also be asexually developed (Zopf, 1884; Scherffel, 1925a; 

 McLarty, 1941a; Karling, 1944g; Sparrow, 1950). 



The process that precedes resting-spore formation in Olpidiopsis has 

 been studied by many observers (Cornu, 1872a; Reinsch, 1878; Fischer, 

 1880, 1882; Butler, 1907; Barrett, 1912b; Shanor, 1939a, 1939b; Mc- 

 Larty, 1941a, 1941b; etc.). In hypertrophied portions of fungous hyphae 

 in which several parasites are developing, certain thalli of unequal size 

 may become associated, usually in pairs. The larger continues to increase 

 in size and its contents become characterized by the production of 

 numerous fat bodies. The two unequal-sized thalli then secrete cellulose 

 walls and are fused together at one point. A pore develops in the wall of 

 contact, through which the contents of the smaller thallus pass into the 

 larger, receptive, body. After the contents have fused, an endospore 

 wall of cellulose forms around the larger thallus. At maturity the outer 

 surface of the wall of the receptive thallus bears on it a considerable 

 amount of material, derived, according to McLarty {op. cit.), from 

 localized deposits of host protoplasm during maturation. This material 

 is usually laid down unevenly and, as a consequence, produces an 

 exospore layer of spiny, tuberculate, fibrillose, or irregular character. 

 The numerous variations found by McLarty in the character of the 

 exospore occurring in cultures of O. achlyae derived from single zoo- 

 spores have rightly brought into question the value of using the exospore 

 wall as a character in distinguishing species. 



The sexual process in Olpidiopsis has been examined cytologically by 

 Barrett (1912b) and McLarty (1941b). Both the contributing and the 

 receptive thalli are at first uninucleate, but by repeated simultaneous 

 mitotic divisions they become multinucleate (Fig. 74 H-I, p. 908). The 

 spindles are intranuclear and the number of chromosomes, according 

 to Barrett, is six. Barrett believes that fusion of the nuclei in pairs occurs 

 after the contents of the smaller thallus have passed into the larger one. 

 This is denied by McLarty, who states that, though plasmogamy does 

 unquestionably take place, there are no nuclear fusions. At germination 

 the resting spore becomes converted into a sporangium (Shanor, 1939a; 

 McLarty, 1941b). No evidences of meiosis could be found by McLarty, 

 and this, together with the absence of karyogamy and the frequent 



