FUNGI: THE RUST FUNGI 



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so called because there is a thin membrane, the remnant of the 

 palets, which covers the mass of smut, so that it does not so readily 

 scatter. There is also another kind of wheat smut, the stinking 

 smut (two species), so called because 

 of its foul odor. This smut injures 

 only the interior of the wheat grain, 

 which it changes to a greasy mass of 

 black smut spores covered by the 

 uninjured seed coats and ovary wall. 

 The grains have the appearance ex- 

 ternally of being perfectly sound, but 

 they are somewhat stouter than the 

 normal grains. Infection takes place 

 as in the case of the oat smut, but 

 the promycelium of the germinating 

 spore is undivided, and the sporidia, 

 which are narrow, long, and slightly ary spores - 

 curved, are borne in a cluster at its apex. 



444. Treatment for the prevention of smut. To prevent 

 the loose smuts of wheat and barley, seed should be selected from 

 fields free from smut. Oat smut and the stinking smut of wheat 

 can largely be prevented by treating the seed wheat with formalin, 

 or by a solution of copper sulphate, or by hot water (at i28-i32 F. 

 for a few minutes). In the case of corn smut infected stalks 

 should be cut out and destroyed before the smut masses ripen. 



Fig. 243. 

 Spores of "bunt," or "stinking 



Rust Fungi (Uredinales)* 



445. The rust fungi. There are a large number of species of 

 rust fungi on grasses, cereals, herbs, trees, and ferns. All of 

 them are parasites, and some cause great injury and loss. The 

 loss to the wheat crop in the- United States is estimated variously 

 from $20,000,000 to $60,000,000 annually. The yellowish or 

 blackish spore masses, often thickly scattered over parts of the 



* The wheat rust can be used for the practical study. If the cluster 

 cup on barberry cannot be had, use other cluster cups. 



