160 DISEASES OF TROPICAL PLANTS CH . 



They are true parasites ; they do not contain chloro- 



Ehyll and therefore cannot elaborate their own food, 

 oon after germination of the seed the young plants 

 attach themselves to the host plants from which they 

 draw their nourishment and cause a reduction in the 

 vigour of the plant, and frequently the death. Oro- 

 banche cernua occurs on the tobacco in India, and 

 0. ramosa in Japan, India, Egypt, Europe, the United 

 States, and Cuba. These two species attack many 

 other plants as well as tobacco, and there are many 

 other species which do not attack the tobacco but do 

 attack other plants. 



The seeds do not germinate unless brought into 

 contact with the roots of the host plants, and many 

 remain in the soil for long periods of time without 

 germinating. 



The plants should be destroyed during the cultiva- 

 tion of the crop so as to prevent their maturing seeds. 

 Care should be taken that the tobacco seed is free from 

 impurities. 



COFFEE 



Rust (Hemileia vastatrix, Berkeley and Broome). 

 This is by far the most destructive disease known on 

 the coffee. 1 The leaves become more or less covered 

 with orange red spots and eventually wither and drop. 

 Parts, and frequently the entire plants, die. The 

 disease reaches its highest development during the 

 rainy season. During the dry season the tree is 

 invaded by superficial mycelial threads, which enter 

 the stomata and feed upon the parenchyma, although 

 but very little external evidence of the disease is to be 

 seen at this time. However, there are a few of the 

 characteristic red spots to be seen at any season of the 

 year, and with the opening of the rainy season these 

 spots become very abundant. They first appear as 

 slightly transparent discolorations which are not easily 



1 This fungus is now believed to have spread to the coffee from some 

 Rubiaceous plant of little or no importance. 



