Minnesota Plant Diseases. 397 



coat over the leaf surface. The sac-capsules appear in the fall, 

 but in some cases do not mature until the following spring. 

 They have appendages somewhat similar to those of the pow- 

 dery mildew of grasses are unbranched, dark in color and inter- 

 woven with the mycelial threads. The capsules contain nu- 

 merous sacs, in each of which are produced eight spores. 



See also Powdery Mildew of Cucumbers. Diseases of Gar- 

 den Crops. 



Powdery mildew of mints (Erysiphc galeopsidis DC.). This 

 mildew occurs on many wild plants of the mint family. The 

 mycelium appears as a superficial whitish film on the leaves and 

 stems. The fungus is very similar to the powdery mildew of 

 vetches and peas. It differs from this fungus in the form of its 

 sucker threads. The sac-capsules are formed in the fall, but 

 do not mature until the following spring. The fungus is not 

 known extensively on cultivated plants. In case of a serious 

 attack the usual methods against powdery mildews would prob- 

 ably be effective. 



Witches'-broom of cherry [Exoascus cerasi (Fckl.) Sad.] 

 See Diseases of Orchards and Vineyards. 



Witches'-broom of birch (Species of Exoascus). See Dis- 

 eases of Timbers and Timber Trees. 



Plum pockets and cherry pockets (Species of Exoascus, 

 chiefly Exoascus pruni Fckl.). See Diseases of Orchards and 

 Vineyards. 



Black-knot of plum and cherry [Ptowrightia morbosa 

 (Scliia 1 .) Sac$.]. See Diseases of Orchards and Vineyards. 



Mold of mushrooms (Sporodinia grandis Link.). Mush- 

 rooms of various kinds, wild as well as cultivated, are attacked 

 by a mold of the bread- or black-mold group. The mold is 

 particularly abundant on mushrooms that have been picked and 

 kept in moist situations for some time. It lives chiefly as a 

 saprophyte and forms on the mushroom a dense, white, moldy 

 felt which is composed of comparatively coarse threads. This 

 white felt later turns brown and then black. When in the 

 brown state one usually finds an abundance of spore-cases, each 

 containing several to many spores. When the felt has become 

 black the sexual reproductive bodies are produced, similar to, 

 but in much greater abundance than in, the ordinary bread 

 mold. Their fusion results in the production of a thick-coated. 



