424 



THE BLACK-SPOT DISEASE. 



times extensively attacked by this parasite, but in America it 

 has not been noticed to any great extent on the more valuable 

 species — its presence being possibly overlooked in meadows be- 

 cause concealed by the spreading blades above, 



A black fungus related to this, which occurs on grass, is Hy- 

 pocrella hypoxylon (Pk.) 



7. The black-spot disease of grass, {Phyllacliora yraminis, 

 P.) Coal-black spots usually under 1-32 in. wide, and 1-32-^ in. 

 long, on the leaves of grasses ; especially conspicuous on the up- 

 per side. 



This is one of the commonest and most no- 

 ticeable of grass-diseases, especially toward 

 the end of the season, but does little harm to 

 valuable species. It is most abundant on 

 quack grass, hedgehog grass and the broad- 

 leaved Panicum. The black spots are com- 

 posed of dense mycelium. In them, usually 

 after the death of the leaf, oval colorless spores 

 Fig. 168. are formed in asci. These sjoores carry the 



species over the winter. Smaller spores (stylospores) are pro- 

 duced in the same spots earlier, and serve for summer propaga- 

 tion. If the disease should prove troublesome, the grass may be 

 cut early before the fungus develops, and the meadow should be 

 burned over on the approach of cold weather to destroy the form- 

 ing winter spores. (Fig. 1G8 illustrates the above species.) 



8. The hlack-spot disease of clover, {Phyllachora trifolli, 

 P.) On the lower side of clover leaves, forming at first dull-black 

 patches, often ^ in. across ; later occurring in the form of slightly 

 glossy-black dots, 1.64 in. in diameter, on small whitish or pale- 

 brown spots. (See Fig. 169.) 



