SAPROLEGNIALES 157 



groups prior to their germination bj^ swarm spores; 

 oosphere typicallj' centric with many oil drops. 



3. Calyptralegnia, p. 162 



B. Oogonium containing a single eccentric oosphere. 



1. Mycelium well developed, of the usual water mould type, not 

 depauperate; sporangiospores after encysting within the 

 sporangium, escaping from the cysts as laterally 

 biciliate swarmspores and passing to the outside through 

 individual pores in the sporangial wall; the emptied poly- 

 hedral cyst walls giving the emptied sporangium the aspect 

 of a net. 



4. Dictyuchus, p. 162 



'2. Mycelium depauperate, forming a dense opaque mat. 



a. Sporangium in form and method of dehiscence corre- 

 sponding to Thrausiotheca; encysted sporangiospores 

 extremely variable in size and shape; germination by 

 swarmspores or by germ tubes in different species. 



5. Brevilegnia, p. 164 



6. Sporangium containing a single row of large spherical 

 to elongate encysted spores which are finally freed by 

 disintegration of the persistent sporangial wall and 

 / germinate by germ tube; swarmspores unknown. 



6. Geolegnia, p. 164 



II. Sporangiospores not normally encysting within the sporangium, escap- 

 ing through a terminal pore. 



A. Sporangia typically ovoid, not proliferating; swarmspores mono- 



planetic, with terminal cilia; oogonia usually 1-spored. 



7. Pythiopsis, p. 165 



B. Sporangia clavate to cylindrical; swarmspores diplanetic. 



1. Sporangia usually clavate; swarmspores arranged irregularly 

 in the sporangium; oogonium usually several- to many- 

 spored. 



a. Swarmspores escaping separately from the sporangium, 

 not encysting at its mouth. 



(1) Sporangia proliferating, the secondary sporangia 



not developed on lateral branches below the 

 primary. 



8. Saprolegnia, p. 167 



(2) Secondary sporangia arising cither by prolifera- 



tion or by lateral branching. 



9. Isoachyla, p. 167 



6. Some or all of the swarmspores encysting at the mouth 

 of the sporangium. 



(1) All of the spores encysting; sporangia not pro- 

 liferating, the secondary developed as lateral 

 branches below the primary. 



10. Achlya, p. 167 



