210 AGRICULTURAL EXPERIMENT STATION. [Jan. 



13. Powdery mildews (^Perisporiacem) are external para- 

 sites of herbaceous parts of plants. The white threads of 

 the mycelium spread over the surface, sending absorbing 

 organs into the tissues, and bear abundantly the fruiting 

 structures, -which are recognizable by the naked eye as tiny 

 black bodies, when ripe. Each of these bodies consists of 

 a hard shell, surroundino^ from one to several somewhat es^g- 

 shaped sacs, in which the spores are contained. The best- 

 known of these fungi are the powdery mildews of the grape 

 and the gooseberry. 



14. Black fungi (^Pyrenoyhycetes) may be so called from 

 the fact that a large majority of them produce a blackened, 

 carbonized appearance of the leaves or liranches which they 

 attack, making them look as though burned. Sometimes, 

 however, they are of a light or bright color, so that the 

 name is not entirely appropriate. In cavities in these black 

 or colored fruiting structures are contained the spores, 

 enclosed in oblong or club-shaped sacs, which escape into 

 the air through tiny pores connecting with the exterior. 

 Many of these fungi also produce summer spores, on threads 

 which cover the outer surface with a "bloom," or line 

 cavities similar to those which contain the spores in sacs. 

 Most of these plants are saprophytes, but a few attack 

 hosts still living. Of them there are a few which are too 

 well known, notably those which cause the " black-knot" of 

 plum and cherry trees, and the " black-rot" of the grape. 



15. Saucer fungi (Discomycetes) are so called from the 

 form of the fruiting portion of many members of the group, 

 though, on account of their wide variations, no single 

 descriptive term is applicable to all. They are chiefly 

 saprophytes, and the larger forms sometimes strikingly 

 recall the toadstools in habit and place of growth. The 

 spores are contained, as in the last two groups, in closed 

 sacs, which, in the saucer fungi, stand erect and closely 

 packed tngether on the upper or inner face of the saucer, 

 which they cover with a distinct spore-bearing layer. A 

 few of these fungi live, at least under certain conditions, as 

 parasites, and develop small sclerotia in the tissues of their 

 hosts, thus producing the so-called " sclerotia diseases " of 

 clover, onions, hemp, etc. 



