DEVELOPMENT OF PLANTS 



257 



spring, variously shaped masses of hyphae bearing numerous 

 teliospores radiate out from these galls and in the early spring 

 rains these strands swell up, forming conspicuous yellow, jelly- 

 like masses. The basidiospores are developed in the jelly and 

 infest the leaves of the apple, thorn, shadbush, etc. In some 

 of the genera of rusts all the stages appear upon the same plant 

 as in the May apple and jack-in-the-pulpit. In the early spring 



Fig. 165. A rust, Gymnosporangium, that infests the juniper and mem- 

 bers of the apple family: A, cluster cups on leaf of thorn apple. B, telio- 

 spore stage on red cedar, juniper. 



the stems and leaves may often be seen infected with the yellow 

 cluster cups which are followed later by the dark-colored teli- 

 ospores. In other cases, teliospores only are produced, as in the 

 hollyhock, and this was doubtless the original form of the spore. 

 Numerous physiological species have been reported among the 

 rusts as in the case of the powdery mildews, and in both groups 

 we find some of these specialized forms able to grow upon differ- 

 ent plants if an intermediate plant is used to "bridge" them over. 

 Thus a physiological species that grows normally upon the oat 

 but not upon rye or wheat may be made to do so by first growing 

 it upon barley. Spores derived from the barley will now infest 

 rye or wheat. 



96. Order b. Ustilaginales or the Smuts. — These parasites 

 are more primitive than the rusts to which they are doubtless 

 17 



