I 



KEYS TO THE FAMILIES AND GENERA OF SAPROLEGNIALES 121 



or a gametangium. Zoospores forming in a vesicle at the tip of the exit tube. 

 In fresh-water algae, pollen grains, and microscopic aquatic animals, etc. 



Thallus strongly constricted at each septum. Antheridial cell poorly differ- 

 entiated. Myzoajtium 



Thallus not, or only slightly, constricted at the septa. Antherids sharply dis- 

 tinguished from the oogones, with well-developed conjugation tube. Some- 

 times septa fail to be formed. 



Lagenidium 



Thallus and sexual reproduction much as in Lagenidium, but no zoospores 

 formed. Aerial conidiophores discharge the single conidia violently from the 

 apex. See Ancylistes 



in Order Entomophthorales (Chap. 7) 



Key to Family Thraustochijtriaceae 

 Single genus. Epibiotic zoosporangium with rhizoids. Thraustochytrium 



Keys to the Families and Genera of Saprolegniales 



Key to the More Important Genera of Family Saprolegniaceae 



(Based in part upon Coker and Matthews, 1937) 



Fertilization of oogones reportedly by uniflagellate sperm cells, otherwise as in 

 Saprolegnia. Probably a species of the latter with Chytridiaceous 

 or Protozoan parasites. Archilegnia 



Oogone fertilized by male nuclei introduced from adhering antherids; develop- 

 ment sometimes parthenogenetic. 

 Sporangia rare or wanting, the spores encysting in the sporangium without a 

 swimming stage and germinating by germ tubes, very rarely by 

 swimming cells. Aplanes 



Sporangia abundant, the spores encysting within them. 

 Oogones usually with more than one egg. 



Encysted spores liberated by the irregular rupture of the sporangial wall, 

 then germinating by germ tubes or by emergence of zoospores of 

 the secondary type. Thraustotheca 



Encysted spores liberated in successive groups by the breaking off of the 

 apical portion of the sporangium, later germinating by emergence 

 of zoospores of the secondary type. Calyptralegnia 



Encysted spores escaping as zoospores of the secondary type through 

 exit papillae which pierce the zoosporangium wall. Mycelium very 

 slender, growing on keratinized media. Aphanodictyon 



Oogones with only one egg. 



Mycelium of vigorous and extensive growth; encysted spores in several 

 rows producing a net-like appearance, germinating by germ tubes 

 or more often by emergence of zoospores of the secondary type. 



Didtjuchus 

 Mycelium of very limited growth, dense and opaque. 



Encysted spores in one to several rows, thin-walled, escaping by disso- 

 lution or rupture of sporangial wall, usually germinating by germ 

 tubes, more rarely by emergence of zoospores of the secondary type. 



Brevilegnia 

 Encysted spores in one row, thick-walled, multinucleate, never forming 

 a swimming stage. Geolegnia 



