194 MORPHOLOGY. 



Promycelium bears four sterigmata and four gonidia (or spo- 

 ridia), which in favorable conditions pass back to the bar- 

 berry, germinate, the tube enters between cells into the 

 intercellular spaces of the host to produce the cluster cup 

 again, and thus the life cycle is completed. 



410. Other examples of the rusts. Some of the rusts do great injury to 

 fruit trees and also to forest trees. The ''cedar apples" are abnormal 

 growths on the leaves and twigs of the cedar stimulated by the presence of 

 the mycelium of a rust known as Gymnosporangium macropus. The 

 teleutospores are two celled and are formed in the tissue of the "cedar 

 apple" or gall. The teleutosori are situated at quite regular intervals over 

 the surface of the gall at small circular depressions, and can be easily seen 

 in late autumn and during the winter. A quantity of gelatine is developed 

 along with the teleutospores. In early spring with the warm spring rains 

 the gelatinous substance accompanying the teleutospores swells greatly, and 

 causes the teleutospores to ooze out in long, dull, orange-colored strings, 

 which taper gradually to a slender point and bristle all over the "cedar 

 apple." Here the teleutospores germinate and produce the sporidia. The 

 sporidia are carried to apple trees where they infect leaves and even the 

 fruit, producing here the cluster cups. There are no uredospores. 



G. globosum is another species forming cedar apples, but the gelatinous 

 strings of teleutospores are short and clavate, and the cluster cups are 

 formed on hawthorns. G. nidusavis forms "witches brooms" or "birds 

 nests" in the branches of the cedar. The mycelium in the branches stimu- 

 lates them to profuse branching so that numerous small branches are devel- 

 oped close together. The teleutosori form small pustules scattered over the 

 branches. G. clavipes affects the branches of cedar only slightly deform- 

 ing them or not at all, and the cluster cups are formed en fruits, twigs, and 

 leaves of the hawthorns or quinces, the cluster cups being long, tubular, 

 and orange in color. 



