The Sterile Fungus Khtzoctonia. 



75 



most part very slightly, if at all, colored, and on the outside of the 

 stem and on the roots, where they are often light brown in color. 

 When the hypha; occur in scab ulcers, those near the surface are 

 brown, while the deeper-lying ones are colorless. The sclerotia on 

 the stems and those on the tubers are essentially the same. They 

 are irregular in outline and vary in size from a mere speck to the 

 size of half a pea or even 

 larger. When dry they 

 are dirt colored, and it 

 is difficult to distinguish 

 them from particles of 

 soil adhering to the 

 tubers. This probably 

 accounts for their hav- 

 ing been so generally 

 overlooked. But when 

 wet they become dark 

 brown and very con- 

 spicuous, particularly on 

 the hght skinned varie- 

 ties of potatoes. In spite of vigorous washing, sufficient to 

 thoroughly remove the soil from the tubers, the sclerotia remain 

 firmly attached. Two housekeepers whose attention we have called 

 to the matter assure us that they have long observed that when 

 potatoes are ^^repared for baking there are often found dark brown 

 irregular bodies which are exceedingly difficult to remove by wash- 

 ing. It is necessary to use a scrubbing brush to get rid of them. 

 We suspect that these sclerotia are well known to many of the more 

 observant housekeepers. 



The amount of damage done by the Rliizoctonia when it attacks 

 the subterranean stem and roots of the potato is as yet undeter- 

 mined, but that the fungus is, in some cases at least, a parasite there 

 is little doubt. Where it occurs on the tubers, all of our numerous 

 observations go to show that it is not injurious to them. While the 

 RhizoGtonia hyphge may be abundant in scab ulcers there is no evi- 

 dence that they have anything to do with the formation of the 

 ulcers. The sclerotia are usually seated on the uninjured skin of 



22. — Hyplm (f the potato Rhizoctonia ; from draw- 

 ing by Mr. Sirrine. 



