\m 



Aphanomyces phycophilus De Bary. 



Paul Weatherwax. 



While some experiments were being made witli alg;e about tlie first of 

 March, 11)13, it was noticed that some Spii-ogyra that had been kept for t(n 

 days in distilled water had been attacked by a fungus. Attention was ^t 

 once given to this parasite, wliich was rapidly destroying the alga, 

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

 fication as AphfDwmyccs i)h}/cophili(s De Bary. 



This fungus, which is one of the few parasitic forms of the Saprolc 

 acea.', was first described by De Bary in 1S60, and as late as 18!»2 Hur 

 phi ey * noted that it had not yet been reported from America. Since the i, 

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

 this country. ** 



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

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

 the sterile filaments the host was Spirogiira diibia Kg. Scattered filamem 

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

 attem]»ts to inoculate other species failed. 



The mycelium traverses tlie algal filament lengthwise, sometimes as 

 single thread, but 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 fungi 

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

 and the cell walls break down. 



The mycelium is regular in size and shape, sparingly branched and noi 

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

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



* James Ellis Humphrey, The Saprolegniacese 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** Since writing this article attention has been called to a .set of unpublished drawings made by 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 189.3. These drawings and the loca- 

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

 herein described. 



