126 DISEASES OP CSOPS. 



infested leaf of wheat is examined under a low power of 

 tlie microscope, it will be seen covered (more or less) with 

 sori somewhat similar to those of Puccinia mixta (see 

 Fig. 18 A and B). These sori of a bright-yeUow colour 

 rupture the epidermis of the leaf. If a transverse section 

 of a small sorus is examined under the higher powers of 

 the microscope, a mass of oval -shaped spores is easily- 

 discovered, supported on erect hyphal filaments rising 

 from a densely matted mycelium which passes between 

 the cells of the host-plant. The yellow spores (uredo- 

 spores) of this fungus are liberated by bursting the 

 epidermis of the infested plant. These spores are wafted 

 about by air currents, and may ultimately fall on the 

 leaves of wheat plants, where they germinate by giving 

 rise to hyphse. These hyphae pass into the interior of the 

 infested plants through the stomata. The production of 

 mycelia and spores goes on for many weeks. 



Later in the season the Uredo spots disappear, and 

 black spots, belonging to the second stage in the life- 

 history of this fungus, make their appearance. These 

 small black spots are the sori of the mature P. rubigo- 

 vera, and are seen upon an infested wheat-stem. When 

 these sori are examined under a low power of the micro- 

 scope they have a similar appearance to those represented 

 in Fig. 37 B. If a thin transverse section of a small 

 sorus is magnified 100 diameters, an appearance somewhat 

 resembling Fig. 18 will be observed. The epidermis 

 of the host-plant is ruptured at certain points where com- 

 pound spores (teleutospores) protrude. The teleutospores 

 are supported on erect (more or less) hyphse rising from 

 a densely matted mycelium (spawn). The teleutospores 

 (resting-spores) of P. rubigo-vera are developed in the 

 autumn, and then hibernate until the following spring. 



