84 Minnesota Plant Life. 



There must be at least a thousand different kinds of leaf-spot 

 fungi growing in Minnesota. Not all leaf-spot fungi are cer- 

 tainly black fungi; but the great majority of them belong to 

 that group. Neither do all leaf-spot fungi develop fruit-bodies, 

 for some of them are able to form only a simpler sort of spore- 

 cluster. Yet in most instances it is believed that this is because 

 the fungus has abandoned for some reason the formation of 

 true fruit-bodies. As already observed in the account of the 

 wheat rust a most instructive object of study a fungus may 

 acquire the habit of developing one kind of fruit-body upon 

 one leaf and another kind upon another. It is very probable, 



FIG. 30. Fungus spot-disease of strawberry leaf. After Bailey. Bull. 79, Cornell Univ. Ag. 



Expt. Station. 



v/here leaf-spot fungi fail to develop their ordinary fruit-bod- 

 ies and provide themselves with spore clusters, that they 

 may on other plants develop the true fruit-bodies, or that 

 they have, as is often probable, ceased altogether to produce 

 them. 



Not only do these spot-fungi find pasture upon the tissues 

 of living leaves but closely related forms browse upon old pieces 

 of paper, upon straw, leather, decaying cloth, the shells of nuts 

 and seeds, and even upon such curious fields as the inner sur- 

 face of roasted chestnuts, the feathers of fowls, the hair and 

 hoofs of cattle, and, in short, wherever they can find food-ma- 

 terials suitable for their growth. 



