428 THE SCLEROTIUM DISEASE OF CLOVER. 



Draining the soil well, and especially replacing clover for 

 several years by wlieat, corn, or other crops not attacked by 

 the Sclerotinia, are recommended where it appears. 



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

 the resemblance of their fruit to the conidia or stylospores of 

 Ascomycetes. beveral of these cause diseases of grasses. 



The brown-spot disease of pigeon- 

 grass, early spear-grass, and other species, 

 is due to Septoria graminnm, (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 

 Fig. 173. parasite, within which slender colorless 



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

 by a related fungus (DilopJiospom graminis, Desm.) whose spores 

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

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

 grasses. Mastigosporium alhim, (Riess), and Scolecotrichum gram- 

 inis, (Fckh), cause diseases of the leaves of grass in Europe. The 

 l^'.st named appeared on orchard grass in great abundance about 

 Madison, Wisconsin, in 1886. Hadrotrichum 2)hragmitis, (Fckl.), 

 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 (Cke.), 

 another imperfect form that bears pear-shaped conidia on threals 

 that protrude through the stomata of the gray spots. 



Sporoiolus indicus, a grass of the Southern States, somewhat 

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

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

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

 sporinm ravenelii, (Curt.), that is often so abundant as to form a 

 Fig. 17'i.— Septoria graminwm 



