THE LEAF-SMUT OF TIMOTHY. 



415 



grasses, whicu are finally reduced to brown shreds, covered with 

 dusty spores. 



The first appearance of this disease is in. the 

 formation of lead-colored, thickened lines, 

 about 1-64 in. wide and 1-16 to in. long, be- 

 tween the nerves of the leaf. The epidermis, 

 which at first covers them and gives them their 

 gray color, soon breaks away, revealing a pow- 

 dery mass of black-brown spores, which are ir- 

 regularly rounded or egg-shaped, and closely 

 studded with short spines. They measure 10- 

 12 micro-millimeters, and in their microscop- 

 FIG. 159. i ca l characters closely resemble the spores of 



the corn-smut. 



Similar black lines are formed in the leaves of species of Glyce- 

 ria by Ustilago longissima (Sow.) which has smooth brown spores, 

 3.5 to 7 micro-millimeters in diameter, and in the leaves of wild 

 rye and other grasses by Urocystis occulta (Wall.) the dark 

 brown opaque spores of which measure 10-20 micro-millimeters, 

 and usually occur in clusters of 2-4, closely surrounded by masses 

 of half-round, colorless cells of slightly greater diameter. 



Ustilago hypodytes (Schl.) occurs on the stem of quack grass 

 and other species, usually forming black smut masses inside the 

 leaf -sheath, and U. grandis (Fr.) causes cat-tail-like swellings on 

 the interned es of the reed. 



The fruit of many grasses is replaced by otker smut fungi, the 

 number of which is very considerable. The commonest are: 

 Ustilago panici glauci (Wall.), very abundant in autumn on 

 pigeon grass; U. rabenhorstiana (Kuehn), on crab grasses and 

 sand burs; and U. segetum, (P.), in oats, barley, wheat, etc. 



Draining the soil well, transferring the crops to new land 

 when they have begun to smut badly, and exercising care with 

 respect to manure are preventive measures. 



