New York Agricultural Experiment Station. 505 



diseased tubers. So far as I can learn the disease appeared only 

 to a slight extent on Long Island in 1894, and not at all in 1895. 

 Prof. Green writes that he has heard of no case of the disease 

 occurring in Minnesota in 1895, although diseased tubers were 

 planted in various parts of the State. In Minnesota the disease 

 is known as "rot" or " brown rot." Prof. Green calls it "In- 

 ternal Brown Rot of Potatoes." Inasmuch as the disease is in 

 no sense a rot, I prefer to use the name at the head of this 

 article. 



The cause is not clear. That it is not caused by insects, fungi 

 or bacteria is quite certain for the following reasons: 



(1) The brown spots are frequently entirely surrounded by 

 healthy tissue and have no communication whatever with any 

 portion of the surface. 



(2) Agar-agar cultures made from diseased tissue produced 

 no growth. Attempts to communicate the disease to healthy 

 tubers failed, and diseased tissue placed in a sterilized moist 

 chamber produced neither bacteria nor fungi. 



(3) A careful microscopic examination of the spots shows no 

 disorganization of the tissue, no diminution in the amount of 

 starch, no fungi and no bacteria. 



The cause is probably a physiological one. Certain conditions 

 of growth, perhaps, bring about certain changes in the tuber. 

 There are some reasons for believing that rapid growth favorm 

 the disease. One of these reasons is the fact that the small potn 

 toes, or " seconds," are seldom affected. The small potatoes aie 

 produced late in the season, when growth is slow. 



The disease materially injures tubers for cooking purposea, but 

 the tubers appear healthy and are fre(iuently disposed of before 

 the disease is detected. Hence complaints usually come from con- 

 sumers and dealers, rather than from producers. If the diseased 

 tubers are fit for seed they should be put to that use? Here, two 

 questions arise: 



(1) Will the disease reproduce itself in the crop? 



