1 66 THE SAPROLEGNIACEAE 



obscuring the oogonial stalk; the contents emptying completely into the 

 oogonium. 



Collected only once and then in a little wet weather branch on the 

 north border of Strowd 's low -ground meadows (No. i of March 8, 1922). 



In some respects the present species resembles A. scaber. The size of 

 the oogonia in the two plants is about the same. In A . scaber the oogonial 

 walls may be set with numerous short warts or prominences, or may be 

 merely irregularly roughened, while in the former the oogonial walls may 

 be covered with blunt spines or with long, conspicuous, sharp spines, the 

 walls approaching most often the latter condition. Thus the most uneven 

 type of oogonia in A. scaber resembles the least spiny type of ^. parasitic^. 

 The two plants are readily distinguished by their antheridia: in the Chapel 

 Hill form of A. scaber the antheridia are absent; in the Massachusetts form 

 (Humphrey) the antheridial branches are of androgynous or diclinous 

 origin, the antheridia are small and are not present on all the oogonia. 

 In A. parasitica^the antheridial branches are of diclinous origin, the an- 

 theridia are large and are present on all oogonia. 



The present form could hardly be confused with any other described 

 species of Aphanomyces. In A. stellatus t\\e la-rgev oogonia are covered 

 with thick, blunt papillae and there are several, usually androgynous, 

 antheridia on each oogonium. In A. laevis spines are totally absent from 

 the oogonial wall but quite often the wall is angular. In A. phycophiliis, 

 a form parasitic upon algae, the oogonia have small sharp spines, but 

 the oogonia and eggs are much larger. Of the three species added since 

 deBary established the genus Aphanomyces, all are either insufficiently 

 known or of doubtful validity. In A. coniger Petersen (doubtful species) 

 the oogonia are 30-40iA thick, and in A . norvegicus the oogonia are borne 

 outside the host and ha\e brown walls. 



In its parasitic habit this plant is exacting. Several Achlyas have 

 been successfully inoculated with the parasite, but the plant refuses to 

 grow on Aplanes Treleaseanus or Isoachlya unispora. Four attempts 

 have been made to grow single spores from the parasite on corn meal agar, 

 but the spores in each case refused to sprout. Epiphytic threads of the 

 parasite ha^'e been cut out and placed on corn meal agar, termite ants 

 and pieces of boiled corn grain, but no growth took place. Single 

 Achlya threads, apparently exhausted by the parasite, were placed on 

 corn meal agar. The Achlya threads sprouted and grew but no Aphan- 

 omyces threads were recognizable until after the Achlya threads had 

 attained a length of about two centimeters, and then the threads of the 

 parasite were seen within the Achlya threads. All efforts so far to grow 

 the plant apart from an Achlya have been unsuccessful. 



