DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 503 



The urediniospores are about 22-26/x by 18-20/x, and repeated 

 crops of these may be produced. The teliospores are formed in sori 

 with the urediniospores, as the season advances. They are one- 

 celled, thick walled and measure 20-35/x by 15-22^- The teliospores 

 germinate in the ordinary way by the formation of a four-celled 

 basidium each producing a basidiospore. No satisfactory method 

 of controlling clover rust is known. 



Coffee (Cojfea arabica, L.) 



Leaf-spot {Cercospora caffeicola, B. & €.).■ — The leaves and fruits 

 of coffee plants in the Dutch East Indies, Mexico, Cuba, Jamaica, 

 Trinidad and Brazil are attacked by the leaf-spot fungus, which causes 

 large blotches at first visible only on the upper leaf surface. The spots 

 are dark brown at first, later becoming grayish above and clear below. 

 The center of these blotches die and here the spores are borne. The 

 disease causes the leaves to fall, thus reducing the vigor of the plant 

 and preventing the proper maturing of the coffee berries. Infected 

 berries fall before ripening. 



Rust {Hemileia vastatrix, Berkeley & Broome) .^ — The coffee rust is 

 widely spread through the coffee-growing regions of the old world, 

 and it has been reported from the American tropics, but there is some 

 uncertainty about reports. It is the most destructive disease of the 

 coffee plant and American coffee growers should be on the lookout 

 for it. 



Orange-red spots appear on the leaves, which finally wither and drop, 

 and frequently parts or whole plants die, especially during the rainy 

 season, when the red spots increase in number. The spots appear as 

 shghtly transparent discolorations, which are not easily observed until 

 the leaf is held up to the Hght. An older spot is yellow in color and then 

 a bright orange color. They vary in size, but are usually circular in 

 outhne, and increase in number during June and July, when the disease 

 reaches its culmination, if the weather conditions are favorable. The 

 spores are produced in great abundance in the orange-red spots and on 

 being set free are carried by the wind and insects to other coffee plants 

 on the leaves of which they germinate sending a germ-tube into the 

 leaf through the stomata. The urediniospores 35 to 40/x by 25 to 28ju 

 are single, usually egg-shaped, provided with a papilla and without 



