246 



RUSTS (UREDINE^S) 



appropriate Grass, whereupon hyphae grow out through special 

 thin areas of the wall (Fig. 131, /), to start a fresh generation 

 of the Rust. In this way the disease rapidly spreads during 

 the summer months. 



In rare cases the Fungus may persist through the winter by 



FIG. 131. Rust of Wheat (Puccinia graminis). a, small part of leaf of 

 Barberry, showing a group of aecidia ; b, group of uredospores (u.) 

 and one teleutospore (t.) ; c, germinating teleutospore (only the hypha 

 growing from one of the two cells is shown at its full length), with 

 developing basidiospores (ba.) ; d, group of teleutospores, seen in 

 section of leaf of Wheat ; e, section of Barberry-leaf, showing cluster- 

 cups or aecidia (ae.) in two stages of development, and spermogonia 

 (s.) ; /, germinating uredospore. (b, d, and/ after De Bary ; c after 

 Tulasne ; e after Sachs.) 



means of these spores, and possibly also as a parasite on wild 

 Grasses. As a general rule, however, special winter- or teleuto- 

 spores are produced towards autumn, and these remain dormant 

 in the soil until the following spring. The formation of teleuto- 

 spores is evidenced by a darkening of the spots on the Grass- 

 leaves. Microscopic examination shows that they are now caused 



