856 AQUATIC PHYCOMYCETES 



for the diplanetic (dimorphic) nature of the zoospore. Thus, in Eepto- 

 mitus lacteus and Apodachlya brachynema the first swarmers to emerge 

 are of the primary, apically biflagellate type (Hartog, 1887; Coker, 

 1923; Shen and Siang, 1948; Tndoh, 1953) (Fig. 69 B, I, p. 875). 

 These quickly come to rest and encyst, and from each cyst a laterally 

 biflagellate secondary zoospore eventually issues (Fig. 69 J-K). In A. 

 pyrifera (Zopf, 1888; Shen and Siang, 1948), however, there is a pro- 

 nounced tendency for the immediate encystment of the primary swarmers 

 at the orifice of the sporangium (Fig. 69 E). In the Rhipidiaceae the 

 primary swarm stage is apparently suppressed, although it is possibly 

 represented by the exceedingly ephemeral vesicle which is some- 

 times formed (Thaxter, 1896b) (Fig. 71 B, p. 894). The zoospores of this 

 family are exclusively of the laterally biflagellate type (Fig. 71 F). There 

 have been no reports except in Mindeniella spinospora (Sparrow and 

 Cutter, 1941) of the repeated emergence of the secondary zoospores. 

 The zoospores of most species of the order show no unusual features. 

 In Araiospora spinosa, Rhipidium, and Mindeniella, however, they are 

 unique and striking objects by reason of the presence within the contents 

 of great numbers of colorless refractive globules (Fig. 71 F, p. 894; Fig. 

 72 C, p. 902). The body of the zoospore, although differing somewhat 

 in the various genera, conforms for the most part to the "kidney-shaped" 

 or "bean-shaped" configuration common to all zoospores of the second- 

 ary type. The flagella are apparently of equal length, oppositely direct- 

 ed, and attached in a shallow groove. 



Sexual Reproduction 



Sexual reproduction is known to occur in the majority of species. It is 

 apparently lacking, however, in Leptomitus lacteus, Rhipidium parthen- 

 osporum, and Mindeniella spinospora, the oospore in the last two species 

 being supplanted as the resting structure by a parthenogenetically devel- 

 oped resting spore (Kanouse, 1927). Where known, sexual reproduction 

 is oogamous. The oogonia originate in the same manner as the zoo- 

 sporangia and either terminate hyphal segments or are borne on the 

 basal cell on short pedicels. Except in the aberrant species Apodachlyclla 

 completa (Humphrey, 1893; Indoh, 1939) only a single egg is formed in 



