164 



VETEKINAEY HYGIENE 



and spots. The colour is due to the spores of the fungus, 

 which can be shaken off the leaf and are found to be of a 

 rusty appearance. These spores, known as uredosjyores, 

 are produced by the growth of a mycelium in the substance 

 of the leaf, and should they get detached from the plant 

 by air currents or otherwise, and fall on members of the 

 grass tribe, these become infected with rust. 



As the summer advances, the mycelium on the leaf 

 which has been producing the orange-red uredospores, now 



Fig. 27- — Rust and Mildew (Fream). A, part of stem of oat plant attacked by 

 Puccinia graminis ; B, Two of the blotches from A enlarged 20 diame- 

 ters ; C, Puccinia graminis within the stem, but near the surface, burst- 

 ing the cuticle at D, beneath which are seen the teleutospores ; E E, 

 Spores of Urcdo linearis, which sometimes surround the teleutospores of 

 P. graminis; G, Teleutospores genninating and producing sporidia at H. 

 These sporidia on germinating give rise to ^Scidimn herheridis. 



produces a second kind of spore ; the reddish-yellow lines 

 and spots on the leaf give way to marks of a much darker 

 colour. Finally, the further production of orange-red 

 spores ceases, and only the second kind of spore is formed 

 from the mycelium. This is the condition known as 

 mildew. 



This second spore, known as a teleutospore, is incapable 

 (unlike the first kind) of producing disease if placed on a 

 healthy plant, the fungus must pass through another plant 



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