PARASITIC FUNGI AND MOULDS. 



15 



Basidiomycetes have no endogenous spores, but 

 they may have as many as four forms of exogenous 

 spores. This is the case with the rust of wheat, 

 termed by naturalists Uredo or Pucdnia graminis, 

 which appears in the spring on the blades of this 

 plant. The patches of rust are covered with a fine 

 dust, which, under the microscope, is seen to consist 

 of small elongated bodies of a reddish brown, resting 

 on a filament; these are the first 

 spores of the fungus, and are 

 termed uredospores (Fig. 5). If 

 they are scattered over a blade 

 of wheat which was previously 

 healthy, they germinate by means 

 of a hypha of mycelium, which 

 penetrates the leaf and develops 

 a fresh patch of rust. In harvest- 

 time the patches are of a darker, 

 almost black shade, owing to the 

 development of a second kind of ^^ST^^fS** 

 spore. These are pear-shaped, SS^SftSSi 

 divided in two, with an enveloping ^**ff^ 

 membrane of considerable thickness ; they are called 

 teleutospores (Fig. 5). 



Teleutospores cannot germinate on a healthy blade 

 of wheat, and consequently do not communicate rust. 

 They may remain through the winter on thatch 

 or wheat straw, awaiting the ensuing spring, and 

 even then they cannot be developed upon a blade 



