New York Agricultural Experiment Station. 421 



II. THE COMMUNICABILITY OF POTATO STEM-BLIGHT. 



The iiotato stem-blight herein discussed is the one described by 

 the writer in Bulletin No. 101 of this Station, pp. 83-84. The 

 symptoms of the disease, as there given, are as follows: " First, 

 there is a cessation of growth. The topmost leaves take on a 

 yellowish, or in some varieties a purple color, and roll inward 

 from the edges and upward, exposing the under surfaces. This 

 condition is followed by wilting and complete drying up of the 

 entire foliage, the process taking from one to three weeks. The 

 tubers appear to be sound, but, when cut at the stem-end, black- 

 ened fibers are seen penetrating the flesh to a considerable dis- 

 tance materially injuring it for cooking purposes. No rot de- 

 velops in the tubers. The stem just beneath the surface of the 

 soil first shows discolored spots and later becomes dry and 

 shriveled." 



This disease has continued to be destructive in 1896 and 1897, 

 but the cause of it is still unknown. Formerly, a species of 

 Oospora was suspected of having some connection with it, but it 

 is now very doubtful if any organism is responsible for the 

 tro.uble. The portion of the stem which is below ground is quite 

 evidently the seat of the disease, but no fungus hyphse can be 

 found in the tissues of this part of the plant in the early stages of 

 the disease; neither are bacteria abundant, and the few which 

 are found in the tissues may easily have gained entrance after 

 the death of the stem. Numerous Petri-dish cultures of tissue 

 from the interior of diseased stems were made with varying re- 

 sults. Because of the nature of the disease and the position of 

 the diseased part it is very difficult to prevent the intrusion of 

 foreign germs. While these cultures were in progress portions 

 of diseased tubers were placed in moist chambers, but without 

 exception they failed to develop any growth whatever. This 

 gave rise to the suspicion that the disease may not be due to any 

 organism but is purely physiological. It was, therefore, deemed 

 advisable to determine, by experiment, whether the disease is 

 communicable. 



