280 



Introduction to Botany. 



and appropriates the materials manufactured there. These 

 spores, called summer spores, or uredospores, when brought 



A FIG. 141. 



A, clusters of uredospores of wheat rust breaking through the epidermis 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 slender sprouts which 

 enter the leaf through the stomata, 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 winter spores, or 

 teleutospores, survive 



parasitized by Puccinia. The mycelium of the 



fungus extends through the leaf and bears clus- the Winter, and the 

 ters of teleutospores at the upper surface. following; Spring ger- 



minate and produce filaments, each bearing several small 

 spores (Fig. 143) which may grow into the leaves of barberry 



FIG. 142. 



Photomicrograph of a cross section of a grass leaf 



