384 AQUATIC PHYCOMYCETES 



a sporangium and produces a discharge tube through which the zoo- 

 spores emerge. Karling ( 1 936b : 469), on the other hand, who has observ- 

 ed many instances of germination in this same species, states that the 

 contents emerge through a pore and form a thin-walled zoosporangium 

 sessile to the thick-walled structure. Germination in the latter manner 

 has been witnessed in Diplophlyctis laevis (Richards, 1951). 



Evidence for sexual reproduction preceding resting-spore formation 

 in Diplophlyctis intestina has been presented by Sparrow (1936d). More 

 recently, Haskins (1950) furnished confirmation for it in the case of 

 another species. He observed that in D. sexualis bodies resembling 

 zoospores, which had germinated within small sporangia ("male 

 gametangia"), produced rhizoidal systems which penetrate the wall 

 of the structure bearing them and anastomose with the rhizoidal 

 system of the receptive thallus. The female, after receiving the contents 

 of the male, formed a resting spore. Since asexual resting spores were 

 recorded also it is, of course, a question whether here the "sexuality" 

 is not, in fact, a process of "rejuvenescence" similar to that noted in 

 Chytridium lagenaria (Sparrow, 1936a). Cytological evidence is needed 

 to settle this point, but support for the occurrence of sexuality is given 

 by the failure of the unfused male and female plants to develop. 



As in Entophlyetis, the order in which rudiments of the thallus in 

 members of Diplophlyctis develop varies. Schenk (1858b), Zopf (1884), 

 and Karling (1928b) all show clearly that in D. intestina in a characean 

 substratum, the rudiment of the sporangium is immediately laid down 

 at the tip of the penetration tube by the zoospore and that the apophysis, 

 from which the rhizoidal system emerges, is formed next. The sequence 

 is illustrated in a series of continuous observations by Zopf. A further 

 study by Karling (1930) on this species indicates that the rudiments of 

 the rhizoidal system were first to originate from the germ tube, then 

 those of the sporangia were formed at the tip of one of the diverticulae. 

 Lastly, the apophysis appeared as a swelling between a sporangium and 

 its concomitant rhizoidal element. This second type of development 

 has also been reported in D. laevis by Sparrow (1939a) and Richards 

 (1951). In his study of D. sexualis Haskins (1950), however, states that 

 "at the end of a branch (usually a short lateral one) of a germ tube 

 from the encysted zoospores, a tiny more or less dumb-bell-shaped 



