112 JOURNAL OF THE 



disease of cabbages and turnips vulgarly known as "club-foot/' 

 The surface of a healthy potato is quite smooth with here and 

 there minute rounded elevations which are usually of a little 

 lighter color than the ground color of the surface and sliglitly 

 roughened or granular. These are known as the " lenticels/' 

 the cork cells of which being loose and rounded have many inter- 

 cellular spaces and permit an easy interchange of gases between 

 the cells of the potato and the outside. It is supposed that the 

 potato scab disease begins in the vicinity of these lenticels. An 

 increase in the tissue of the potato takes place here, so that a 

 low convex elevation is formed, the surface of which becomes 

 "scurfy" by the pealing off of the outer coats. From this the 

 tissues break down and decay sets in, and unless the disease is 

 arrested the whole surface of the potato is affected. It appears 

 that the larvae of Heterodera radicicola mainly attack a potato in 

 the vicinity of these lenticels, for the first external sign of the 

 presence of the parasite is the enlargement of tliese lenticels 

 until elevations of considerable size are formed, which are scurfy 

 on the surface. Finally the elevation cracks, decay sets in and 

 in many cases the external appearance strongly resembles a 

 " scabby '^ potato. Usually, however, when the disease is arrested 

 the tissues being softened gradually shrivel and the potato has a 

 wrinkled and shriveled appearance which I never saw in a potato 

 affected bv what is called the "scab.'' Usually also the roots 

 will present the irregularly fusiform or ovoid galls. For the 

 purpose of comparing "scabby" potatoes with those infested by 

 the Heterodet'a requests were made of several gentlemen in Ala- 

 bama and in some of the Northern States for " scabby" potatoes 

 from their respective sections. Specimens were received from 

 Peter Collier,* Director of the New York Agr. Exp. Station at 

 Geneva, N. Y. ; from Prof. E. S. (joff, Horticulturist of the 

 Wisconsin Agr. Ex. Station at Madison, Wis.; from Mr. Clar- 

 ence M. Weed, Entomologist of the Ohio Agr. Exp. Station at 

 Columbus, Ohio; frojn Mr. Wilson Newman, Assistant Director 



*Tlie author wishes to express his obligation to these gentlemen for their kindness. 



