ELISHA MITCHELL SCIENTIFIC SOCIETY. 83 



the plant to recover from the effects of the disease. Tliese roots, 

 in turn, are attacked and deformed as represented in the figure. 

 Other plants were found with the tap root still alive, very much 

 enlarged and cracked, and the disease in an active state. The 

 enlargements of the I'oots of the Irish potato are similar in form 

 to those of the tomato, though on specimens I have examined 

 they are not so large or numerous. The surface of affected 

 tubers first presents minute elevations usually at the point on 

 the surface corresponding to a lenticel. The minute elevation 

 soon grows to be quite a large convex elevation and finally 

 cracks. In the seed potato in tl'e figure, Plate I, the cracks can 

 be seen, while on the young potato represented in the upper left 

 hand corner the projections aie still quite smooth. These char- 

 acters of the disease in the tubers will be referred to again. 



There is great variation in the form of the galls even on the 

 roots of a single species. Plate V, Figures 31 and 32, represent 

 respectively the galls on the roots of the cotton plant and peach. 

 The fibrous roots of the peach possess short ovoid, usually lateral 

 galls; sometimes they are symmetrical. As the root becomes 

 older and the disease spreads the external appearance is more as 

 represented by the larger root in the figure, the surface irregu- 

 larly enlarged, roughened and cracked. 



This description of the external characters of the disease will 

 serve to introduce the subject. A more detailed comparison of 

 the variations in different plants will be given below. 



III. 



MICROSCOPIC CHARACTERS. 



Upon examination the enlargements proved to be the galls 

 produced by the presenee of a nematode worm, Heterodera radi- 

 cicola, Miill.* (Angulllula radiclcola, Greeff,'f AnguiUula arena- 

 ria N.X ex-parie). If we cut directly across one of these tomato 



*Mittheilungen uber unseren Kulturpflanzen schadliehe, das Geschlecht Heterodera 

 bildenden Warmer, Landwirtlischaftliehe Jahrbucher. Band XIII, Heft I, S. 1-42, Ber- 

 lin, 1884. 



fSitzungsberioht. der Marburg Gesell. z. Beford. d. Naturwiss, 1872, S. 169. 



^Bulletin No. 20, U. S. Department of Agriculture, Division of Entomology, Washing- 

 ton, 1889. 



