54 THE SAPROLEGNIACEAE 



of that group except 5. mixta, which has weaker hyphae. The material 

 was cultivated for nearly a year and a half on flies, in agar, and by trans- 

 fer from a strong culture medium such as pea decoction or peptone, 

 into haemoglobin, leucin, peptone, or other solution. During all this 

 time no oogonia were produced. Toward the end of this time a 

 series of tests was made with several cultures by transferring vigorous 

 mycelium to leucin to which various sugars and salts had been added. 

 Among other combinations there was used leucin 555+levulose jhs- 

 and in this a mycelium out of pea extract produced an abundance of 

 oogonia. When these were examined they proved to be indistinguish- 

 able from the oogonia and antheridia of S. monoica Pringsh. Rarely an 

 oogonium was found on which there was no antheridium, but in some 

 solutions this may also be the case with 5. monoica. 



"The fact that cultures of S. monoica were going on at the same 

 time suggested the possibility of contamination. Check cultures were 

 made, therefore, by taking mycelium from the dish in which the oogonia 

 were formed and growing this on fly. Had the mycelium producing 

 oogonia been that of S. moiioica (No. 79c of my series), plenty of oogonia 

 would have been produced. In fact, no oogonia were formed on the 

 fly culture, but a fresh culture from this fly through pea decoction into 

 leucin and levulose again produced oogonia as before. 



"We seem to have here, therefore, the remarkable case of a variety 

 of 5. monoica having lost sexuality, but recovering it under stimulus 

 of this special combination, leucin and levulose in concentration ^0 each. 



"The gemmae of this form are perhaps a little more varied in shape 

 than is the case with the species, but the shape of these organs is so 

 variable in most species that they are of no value for systematic pur- 

 poses. 



"Had time permitted, it would have been interesting to cultivate 

 this form for many generations in leucin-levulose solutions to determine 

 whether the vigorous production of oogonia which characterizes such 

 forms of 5. monoica as my 79c would be regained by this variety. 



"The forms described in this paper are remarkable examples of the 

 intimate dependence of the members of this group on external condi- 

 tions." 



ID. Saprolegnia litoralis n. sp. 



Plates 15 and 16 



Growth about as in Saprolegnia ferax, more vigorous, extensive 

 and irregular than in Saprolegnia delica, the hyphae reaching a length of 

 1-1.5 cm. on a mushroom grub. Sporangia not abundant, far less so 

 than in Saprolegnia diclina, early ones nearly cylindrical, or more often 



