28o 



Introduction to Botany. 



and appropriates the materials manufactured there. These 

 spores, called summer spores, or uredospores, when brought 



w Fig. 141. 



A, clusters of uredospores of wheat rust breaking through the epiderinis between 

 the parallel veins of a leaf of wheat. B, a cross section through one of the 

 spore clusters of A, showing the uredospores highly magnified. 



to other leaves by the wind, put forth 

 enter the leaf through the stomata. 



Fig. 142. 



Photomicrograph of a cross section of a grass leaf 

 parasitized by Puccinia. The mycelium of the 

 fungus extends through the leaf and bears clus- 

 ters of teleutospores at the upper surface. 



minate and produce filaments, each 

 spores (Fig. 143) which may grow into 



slender sprouts which 

 and thus within the 

 leaf new rust plants 

 are started, which in 

 turn produce summer 

 spores. 



Later in the season 

 spores are formed 

 which are two-celled, 

 pear-shaped, and 

 darker in color (Fig. 

 142) ; these, known 

 as the ivi titer spores, or 

 teleutospores, survive 

 the winter, and the 

 following spring ger- 

 bearing several small 

 the leaves of barberry 



