IGO 



THE LOWER FUNGI— PHYCOMYCETES 



of the genus and the inclusion of these species in Achlya and 

 Saprolegnia. It should be emphasized in this connection that 

 the sporangiospores of various members of the family may ger- 

 minate in situ under certain adverse environmental conditions. 



2. Thraustotheca Humphrey (1893: 131). 



Until recently the type species, T. clavata (de Bary) Humphrey, 

 comprised the genus. Although relatively rare it occurs both 

 in Elurope and America, and has been studied by various investi- 

 gators. Earlier workers (Humphrey, 1893: 131) believed the 



Fig. 56. — Thraustotheca clavata (do Bary) Humphroy. («) Mature sporangium. 

 (b) Escape of sporangiospores (After IVenton 1918.) 



sporangial wall to be very fragile, and described the encysted 

 sporangiospores as escaping only by its disintegration. This view 

 has been taken also by Coker and Hyman (1912: 88). On the 

 other hand Weston (1918: 160) finds that swelling of the spores, 

 due to imbibition of water, causes an internal pressure which 

 ruptures a normally thick sporangial wall (Fig. 56). The open- 

 ing which results is usually large and may occur at any point. 

 The spores thus freed then germinate, some by germ tube, others 

 by emission of a reniform, laterally biciliate zoospore (Fig. 57). 

 The genus at present contains one other species, T. primoachlya 

 Coker & Couch (1924: 197). In it the sporangium is said to 



