194 MORPHOLOG v. 



Promycelium l)ears four sterigniata and four gonidia (or spo 

 ridia), which in favoraljle coiKHtions i)ass back to the bar- 

 berry, "germinate, the tube enters Ijetween cells into the 

 intercellular s[)aces of the host to produce the cluster cup 

 again, and thus the life cycle is completed. 



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

 fruit trees and als(} to forest trees. The "cedar apples" are abnormal 

 growths on the leaves and twigs of the eedar stimulated Ijy the presence of 

 the mycelium of a rust known as Gymnosporangium macropus. The 

 teleutospores arc two celled and are formed in the tissue of the '^' cedar 

 apple" or gall. The teleutosori arc situated at <|uitc 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 w'ith the warm spring rains 

 the gelatinous substance acccjmpanying the teleutospores swells greatly, and 

 causes the teleutos])orcs to ooze out in long, dull, orange-colored strings, 

 which taper gradually to a slender [joint and Ijristle all over the "cedar 

 apple." Here the teleutospores germinate and ])roduce the sporidia. The 

 sporidia are carried ti> api)le trees where thcv infect leaves and even the 

 fruit, producing here the cluster cu[.)s. There are no uredospores. 



G. glob(jsum is another species forming cedar apples, but the gelatinous 

 strings of teleutos])ores are sliort and clavate, and the cluster cups are 

 formed on hawthorns. G. nidusavis htrms "witches brooms" (.)r "birds 

 nests" in the branches of the cedar. The mvcehuni 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 alTerts the branches of ( edar only slightly deform- 

 ing them or not at all, and the cluster tups are formed on fruits, twigs, and 

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

 and orange in color. 



