428 THE SCLEROTIUM DISEASE OF CLOVER. 



wheat, corn, or other crops not attacked by the Peziza, are 

 recommended where it appears. As the potato, rape, and hemp 

 sometimes suffer from a similar sclerotium disease, they should 

 not be used in rotation with each other or with clover in case of 

 its appearance. 



A large number of fungi are spoken of as imperfect fungi from 

 the resemblance of their fruit to the conidia or stylospores of 

 Ascomycetes. Several of these cause diseases of grasses. 



The brown-spot disease of pigeon- 

 grass, early spear-grass, and other species, 

 is due to Septoria gramhuim, (Desm.) 

 (Fig. 173), that form a mycelium within 

 the plant, usually killing it in places 

 which turn brown and are finally dotted 

 with the minute black fruit-bodies of the 

 PiQ. 173. pai'asite, within which slender colorless 



spores are produced. In Europe, a similar disease is also caused 

 by a related fungus [Dilophospora graminis, Desm.) whose spores 

 differ in having brush-like appendages at their ends. Both are 

 at times destructive, but affect the cereals more than the smaller 

 grasses. Mastigosporium albu?n, (Riess), and 8colecotrichum gram- 

 inis, (Fche.), cause diseases of the leaves of grass in Europe; the 

 last named appeared on orchard grass in great abundance about 

 Madison, Wisconsin, in 1886. Hadrotrlclium pliragmitis, (Fche.), 

 forms small, dark-brown pustules on leaves of the reed, resem- 

 bling those of a rust-fungus, even under a hand-lens. The gray- 

 spot disease of crab-grass is due to Pyricularia grisea (Che.), 

 another imperfect form that bears pear-shaped conidia on threads 

 that protrude through the stomata of the gray spots. 



Sporobolus indicus, a grass of the Southern States, somewhat 

 esteemed for pasturage while young, is often called '^black-seed 

 grass" or "smut-grass" from the fact that its flowering parts 

 are generally covered by the dark-brown fruit of Helmintho- 



