THE SCLEROTIUM DISEASE OF CLOVER. 437 



white mycelium that bears such numbers of wliite spores as to 

 suggest u dusting of meal or flour. 



This mildew is usually found through the 

 entire open season on grass growing in damp 

 and shaded positions; it is especially abundant 

 on June grass. Its cobwebby mycelium, which 

 does not penetrate the leaves, does not at first 

 appear to injure them but in time they succumb 

 Pia. 173. and dry up. Through the summer it spreads 



by means of its light conidia, that are easily blown about and 

 germinate quickly while fresh, though they are unable to live 

 through the winter. On the dead leaves, small black fruit- 

 bodies, scarcely visible to the naked eye, are formed, in which 

 winter-sj^ores are produced in asci. (Fig. 172 is the illustration 

 for the grass-mildew.) 



Usually grasses do not suffer much from mildew, except in 

 damp and shaded places. Drainage is likely to prove beneficial 

 where it is troublesome, and infested wheat-fields have been 

 advantageously dusted with flowers of sulphur in Europe. 



11. Sclerotium disease of clover, {Sderotinia trifoUonim, 

 Eriks.). On clover, causing a browning of leaves or stem, which 

 are soon covered in spots by a white mold that ultimately forms 

 solid, wavy, black bodies, often ^ in. long, white within. 



In Europe, clovers and medicago are occasionally attacked by 

 this fungus, which is very destructive when it occurs. The 

 entire plant becomes flUed with a mycelium which soon kills it 

 and afterwards breaks through in places, forming black sclerotia 

 on the various parts of the decaying plants as winter approaches. 

 These bodies lie dormant in the soil until the following summer, 

 when they produce fruit-bodies in the form of wavy stems, bear- 

 ing brown disks or inverted cones, -^^ to ^ in. in diameter, on 

 their ends. When these reach the surface they shed their spores 

 and so spread the disease. 



