MAINE AGRICULTURAL EXPERIMENT STATION. 9 



If the stems of potatoes affected in this manner are cut off 

 close to the surface of the ground, either above or below, 

 but more especially the underground portions, it will be seen 

 that they show a ring of discolored or browned tissue a little 

 way below the surface. This is in the region of the water 

 conducting system and undoubtedly the wilting and death of 

 the plant is due to the clogging of the conducting vessels, 

 thus shutting off its water supply. 



The fungus also attacks the roots and tubers. In my expe- 

 rience such tubers as have already formed at the time of the 

 examination of plainly diseased plants usually show some signs 

 of infection at the stem end. This may be indeed slight, just 

 at the junction' of the stem and tuber, or it maj appear in the 

 form of a distinct brownish ring a little below the surface of 

 the potato, and extending some distance from the stem end. 

 The small amount of wilt observed in Maine, while the general 

 effects are similar, appears to be of a slightly different type 

 than that described, in that the growth of the fungus, and the 

 resulting browning of the stem may extend up for considerable 

 distances, often into the leaf stalks. The wilting characteristics 

 are more pronounced, for the plants will often suddenly wilt 

 and die without much previous signs of disease. Regardless of 

 the cause, potatoes from plants so affected should never be 

 used for seed purposes. 



We frequently find in Maine a potato trouble where the dis- 

 eased tubers might- be mistaken for those affected with the wilt 

 fungus. . Here the tissues, usually confined to that portion out- 

 side the vascular ring; show a peculiar mottled browning, or 

 irregular netted appearance. This has been given the name of 

 net-necrosis. There is no evidence that it is of a parasitic 

 nature, but it may indicate a constitutional weakness, therefore 

 tubers so affected should not be used for seed. Even the 

 browning of the vascular ring, in our experience, does not 

 always indicate the ipresence of a parasite that we can discover, 

 but all these things do indicate a weakness of the tuber.* 



Potato leaf-roll, a disease which has been receiving consider- 

 able attention in Germany during the past few years, has only 



♦Experimental work conducted after this article was written, but be- 

 fore publication, has shown conclusively that planting tubers affected 

 with net-necrosis results in a material reduction in yield. 



