SAPROLEGNIACEAE 



Key to the Genera 



I. Sporangia rare or absent; oogonia willi \ery thick pitted walls, the ai'.theridia arising 

 from immediately helow them and running up their sides At>lanes{p.~6) 



1 . Not as above 2 



2. Spores normally leaving the sporangium by a common mouth 3 



2. Spores not leaving the sporangium by a common mouth (see also Aciilya ditbia) 8 



3. Spores all (normally) swarming separately on escaping from the sporangium 4 



,1. Spores all collecting in a hollow sphere or an irregular group at the mouth of the spor- 

 angium on escaping 7 



3. Part of the spores on emerging swimming away or sluggishly jerking away and encysting 



separately from the remainder, which stop at the sporangium mouth. Sporangia 

 rounded at the tip and not tapering, in great part proliferating cymosely as in Aclilya, 

 but at times threads may grow through empty sporangia as in Saprolegnia. Eggs 

 centric Protoachlya (p. 90) 



4. Sporangia not thicker than the vegetative hyphae; zoospores in a single row 



Leploleguia (p. 157) 



4. Sporangia usually thicker than the hyphae; zoospores not in a single row 5 



5. New sporangia formed within the empty ones Saprolegnia (p. 22) 



5. New sporangia formed in greater part by cymose branching 6 



6. Antheridia on every oogonium, androgynous Pythiopsis (p. 17) 



6. Antheridia absent, or on less than half the oogonia, diclinous Isoachlya (p. 81) 



7. Sporangia usually thicker than the vegetative hyphae; zoospores not in a single row 



Achlya (p. 95) 



7. Sporangia not thicker than the vegetative hyphae; zoospores in a single row 



Aphanomyces (p. 160) 



8. Spores encysting within the sporangium, then emerging separately through the spor- 



angium wall and swarming Dictyttchus (p. 150) 



8. Spores set free by the breaking up of the sporangial wall Thraustotheca (p. 148) 



PYTHIOPSIS de Bary, 1888, p. 609. 



Hyphae slender, much or little branched. Sporangia typically 

 short and plump, spherical, oval, pyriform with a distinct apical papilla, 

 or varying to elongated and irregular, primarily borne at the tips of the 

 hyphae and multiplied from lateral stalks below the old ones to form 

 more or less dense clusters. Spores emerging and swimming as in Sapro- 

 legnia, pip-shaped with two apical cilia, sprouting after the first encyst- 

 ment (monoplanetic). Gemmae resembling the sporangia or oogonia, 

 formed plentifully, often in chains, producing zoospores after a rest. 

 Oogonia borne like the sporangia and gemmae and resembling them 

 in youth, typically spherical, oval or pyriform with unpitted walls, 



