Some Potato Diseases. 



and Irish Potato," by Erwin F. Smith. U.S. Dept. Agric. Bull. 



No. 12 f 1 896). 



Description of Figures ( Plate II.). 



1. Section of a potato showing the entrance of the bacterium 

 into the tuber through its underground stem. The discoloured 

 zone is small and indicates a quite recent attack. 



2. Section of a potato showing the disease in an advanced 

 stage. 



III. — Sclerotium Disease of Potatoes. 



Sclcrotinia sclerotiorum (Massee). 



In this instance the tubers are not directly attacked by the 

 fungus, but their growth is either checked or entirely arrested, 

 owing to the destruction of the leaves of the plant. 



The base of the stem just above the ground-line becomes 

 covered with a white fluffy substance, the mycelium of the 

 fungus. This mould gradually grows up the outside of the stem 

 if the atmosphere remains moist and the temperature sufficiently 

 high. After some time the fluffy mould collapses and becomes 

 more compact, and bears numerous variously-shaped black 

 bodies, which sometimes attain the size of a grain of wheat, 

 imbedded in its substance. These bodies, which consist of densely 

 compacted fungus spawn, are called sclerotia. During this 

 period of the development of the fungus the potato stem has 

 become limp and the leaves wilted, and both perish early in the 

 season. 



When the weather is dry and warm, the mycelium extends 

 most vigorously in the hollow of the stem, where numerous 

 sclerotia are formed, very little fluffy mycelium appearing on the 

 surface of the stem. 



Collecting and burning diseased plants is the only certain 

 method of stamping out the disease. If infested tops are left 

 on the ground to decay, the sclerotia remain in the' ground 

 until the following season, when they form reproductive bodies 

 that bear spores which infect the growing crop. In addition to 

 the potato, beans, peas, cucumbers, marrows, turnips, &c, are 

 also attacked ; in fact, probably, every kind of cultivated plant, 



