VII 



POTATOES 209 



and after a few days the leaves become yellowish, show 

 a tendency to curl inward, and die. Furthermore, this 

 disease is not accompanied by the vile odour which is 

 so characteristic of the late blight. 



The disease is due to the fungus Macrosporium 

 solani, 1 E. & M., which is decidedly different from the 

 Phytophthora infestans. The mycelium is also fila- 

 mentous, and after working in the tissues of the host 

 comes to the surface through the stomata and gives rise 

 to numerous, multicellular club-shaped spores. These 

 spores germinate, and the new mycelium readily 

 penetrates the tissues of the host. 



This disease is equally injurious to the tomatoes, and 

 attacks other Solanaceous plants. It can be readily 

 controlled by the use of Bordeaux mixture in the same 

 manner as recommended for late blight. 



Tip Burn, Leaf Burn, or Scald. These are climatic 

 diseases which are frequently confused with the blight 

 diseases. They usually begin at the tips and margins 

 of the leaves and work inward, but do not show the 

 spots which are so characteristic of the blight. 



Rhizoctonia Blight. A great many plants suffer from 

 a soil fungus known as Rhizoctonia. Eecent investiga- 

 tions have led the workers to classify this fungus of the 

 potato, and possibly of many other plants, as Corticium 

 vagum, B. & C., var. solani, Burt. The disease is very 

 widespread, and although the writer is unable to find 

 any record of its occurrence in the tropics, diseases of 

 this class are so common in tropical countries that there 

 is little or no reason to doubt its presence. Further- 

 more, it has been reported from the semi-tropical 

 countries of both hemispheres, and a very similar 

 disease has been reported as destructive in Porto Kico. 

 The fungus attacks the roots, tubers, and other under- 

 ground parts of the stems, spreading over the surface 

 and penetrating the pith. The young stems rot as soon 

 as formed, many of them die, and others are enfeebled. 

 Frequently the tops of those which live are aborted and 



1 Syn. Alternaria solani, E. & M. 



P 



