834 AQUATIC PHYCOMYCETES 



Zoospores in more than one row in the sporangium 



Some of the primary zoospores swimming away upon dis- 

 charge, others encysting in an irregular clump 



Protoachlya, p. 840 

 All of the primary zoospores encysting upon discharge and 

 forming a hollow sphere at the orifice of the sporangium 



Achlya, p. 841 

 Zoospores in a single row in the sporangium or its evacuation tube 

 Sporangium simple, wholly cylindrical 



Hyphal system extensive, without specialized spiny cap- 

 turing elements Aphanomyces, p. 843 



Hyphal system very sparse, composed of a few branches 

 terminated by spines for the capture of microscopic 



animals Sommerstorffia, p. 844 



Sporangium consisting of a cylindrical evacuation tube arising 



from a lobulate basal complex Plectospira, p. 845 



Zoospores encysting within the sporangium before liberation 

 Oogonium with more than one egg 



Sporangia rare, usually lacking; the zoospores usually germi- 

 nating in situ by a germ tube which penetrates the spo- 

 rangium wall Aplanes, p. 846 



Sporangia not rare, zoospores emerging from cysts as motile 

 bodies 

 Cysts liberated from the sporangia; mycelium coarse 



Cysts liberated by deliquescence or tearing of wall of spo- 

 rangium Thraustotheca, p. 846 



Cysts liberated by dehiscence of an apical cap on spo- 

 rangium Calyptralegnia, p. 847 



Cysts not liberated from sporangium; the zoospores emerging 

 through wall of sporangium as motile bodies; mycelium 



delicate Aphanodictyon, p. 847 



Oogonium with a single egg 1 



Mycelium well developed; spores emerging from their cysts 

 through the sporangium wall leaving a network of cyst 



walls within Dictyuchus, p. 848 



Mycelium depauperate, dense and opaque 



Encysted spores variable in size but majority not more than 15 

 \l in diameter, in one to several rows, thin-walled, liberated 

 by deliquescence of sporangial wall or in some species 

 also as in Achlya or Dictyuchus, forming germ tubes or 

 motile zoospores Brevilegm a. p. 848 



1 For an explanation of the terms used in describing the structure of the mature 

 egg (oospore) of the Saprolegniaceae see p. 796. 



