109 



Aphanomyces phycophilus De Bary. 



Paul Weatherwax. 



While some experiments were beiug made with alyte about the first of 

 March, 1913. it was noticed that some Spirogyra that had been kept for ten 

 days in distilled water had been attacked l)y a fungus. Attention was at 

 once given to this parasite, which was rapidly destroying the alga. In 

 about a week it was producing oospores, thus making possible its identi- 

 fication as Aphanomyces phycophilus De Bary. 



This fungus, which is one of the few parasitic forms of the Saprolegui- 

 ace*. was first described by De Bary in 1860, and as late as 1892 Hum- 

 ;)h;ey * noted that it had not yet been reported from America. Since then, 

 as far as we have been able to learn, no one has mentioned finding it in 

 this country. ** 



It is clear that the plant is a parasite, and, in this instance, it seemed 

 confined to the one species of host. As well as could be determined from 

 the sterile filaments the host was Spirogyra duMa Kg. Scattered filaments 

 of other species of Spirogyra in the same vessel were not attacked, and all 

 attempts to inoculate other species failed. 



The mycelium traverses the algal filament lengthwise, sometimes as a 

 single thread, liut more often as two, side by side. (Fig. 5.) Branches 

 may grow for some distance inside the filament of the alga, or they may at 

 once grow through the cell wall of the host and extend for some distance 

 into the water. Decomposition of the alga begins soon after the fungus 

 attacks it; the chloroplasts draw together into a mass and begin to decay, 

 and the cell walls break down. 



The mycelium is regular in size and shape, sparingly branched and non- 

 septate except where reproducing. The diameter of the filaments is from 

 9 to 16 microns; the branches are usually as large as the main filaments. 



* James Ellis Humphrey, The Saprolegniaceae of the United States. 



** Since writing this article attention has been called to a set of unpublished drawings made by 

 Prof. D. M. Mottier, of an unidentified fungus that he found in 1893. These drawings and the loca- 

 tion in which the fungus was found indicate very clearly tliat it was the same species as the one 

 herein described. 



