KEYS TO THE FAMILIES AND GENERA OF LAGENIDIALES 119 



The oospore is thick-walled and roughened areolately. Its manner of 

 germination has not been reported. (Fig. 39 A-D.) 



Araiospora, with four species, grows on vegetable matter in water. It 

 has a thick supporting or storage body from which arise the numerous 

 slender constricted branches bearing the reproductive organs. The zoospo- 

 rangia are of two kinds, ovoid or club-shaped ^^•ith smooth walls, and 

 subspherical and covered with stout spines. The zoospores are similar in 

 each type, being biflagellate and kidney-shaped. The spherical oogones 

 are borne on similar branches, sometimes on distinct plants. They are 

 characterized by a cellular periplasm layer around the oospore. The 

 oogone is fertilized by a basally applied antherid which may arise near by. 

 (Fig. 39 E-G.) 



Mindeniella also has zoosporangia of two kinds. The thin- walled 

 clavate or ovoid sporangia are pedicellate on or near the apex of the stout 

 cylindrical or clavate basal segment. They may be spiny at the upper end 

 or without spines. The resting zoosporangia are ovoid or almost spherical 

 and pedicellate. They are spiny and thick-walled. Their germination has 

 not been observed. No sexual organs are known. 



It is apparent that the Rhipidiaceae form a group of more highly 

 specialized genera which have probably arisen from the Leptomitaceae. 

 Whether the latter arose from the Saprolegniaceae or vice versa is uncer- 

 tain. In view of the somewhat more specialized sexual organs in the 

 genus Apodachlya it is possible that this family arose from the Sapro- 

 legniaceae or that both arose from the Lagenidiales. However it is also 

 possible that the latter represent ends of series of reductions from various 

 ancestral forms in the Saprolegniales and possibly in the Peronosporales. 

 Because of the difference in zoospore structure and in the composition of 

 the cell wall it seems unlikely that these orders have any close relationship 

 with the Chytridiales-Blastocladiales-Monoblepharidales series. 



Keys to the Families and Genera of Lagenidiales 



Key to the Genera of Family Woroninaceae 



I" Plasmodium " forming a cluster ("sporangiosorus") of numerous cellulose- 

 walled zoosporangia or a cluster ("cystosorus") of thick-walled, angular resting 

 spores. Parasitic in Saprolegniaceae and green algae. Woronina 



Plasmodium" becoming surrounded by cellulose walls forming an elongated 

 and sometimes branched thin-walled tube. The contents separate into naked 

 "spore mother cells" each of which produces 8 zoospores. Resting spores 

 unknown. Saprophytic in marine Florideae. Pyrrhosorus 



'Plasmodium" at maturity filling the infected portion of the host and forming 

 its wall pressed closely against that of the host. Forming a single more or less 

 rounded zoosporangium or a row of cylindrical zoosjiorangia. Resting spores 

 where known round and spiny and free from the cell wall of the host. Parasitic 

 in Pythiaceae and Saprolegniaceae. Rozellopsis 



