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MINNESOTA STATE HORTICULTURA.L, SOCIETY. 



a new fungus, and as they are very small the wind carries them 

 readily from tree to tree. Later in the season other dark-colored 

 spores are formed by true fertilization, which takes place when two 

 threads cross each other (as seen in Fig-. 4,5). The young perithecia^ 

 or sporocarps, are at first nearly colorless, then gradually assume a 

 yellow, brown and nearly black color. Such a perithecium (Fig. 3, a) 

 is spherical, flattened upon one side and covered with numerous 

 reticulations, which indicate cells below them. Some reticulations 

 produce peculiar and strangely formed appendages peculiar to 

 powdery mildews. Each perithecium contains a single spore-cavity 

 (Fig. 3, d), in which are eight spores. When this cavity breaks open 

 in spring, the spores escape and start new colonies of disease-pro- 

 ducing fungi. 



All powdery mildews thrive best during a warm and drj^ summer. 

 If such a dry spell is followed b}^ a light rain, the disease appears 

 everywhere as if b}^ magic. Much and heavy rain has the opposite 

 effect, as it washes down the spores or seeds of these plants. As 

 such mildews thrive only upon the outside of their hosts, they are 

 easily reached by fungicides. During the last summer the disease 

 was very common upon a great variety of plants, in fact, nearly all 

 the members of the rose family were more or less affected. As a 

 number of shad-berries (Ainelanchier Canadensis) were badly 

 infested behind my house, I tried a number of remedies and found 

 that powdered sulphur dusted over the diseased foliage destroyed 

 all traces of the fungus. Some plants of spiraea, equally badly in- 

 fested, were treated with a liquid fungicide in the form of a fine 

 spray. Potassium sulphide or sulphuret of potassium proved 

 excellent. One-half ounce of this substance was dissolved in one 

 gallon of water. This fluid is also an excellent remedy against the 

 gooseberry mildew, as I had an occasion to prove. 



The Brown Rot of the Plum-Fkuit. (Fig. -i.) 

 ( Monilia fructigena, Pers.) 



Fig. 4. Brown RoT; a, 6, germinating spores and mycelium; c, spores ar- 

 ranged in chains; d, diseased leaf; e, diseased fruit, and others in which the 

 disease was produced artificially; a, h, c, greatly enlarged; r/, e, natural size. 



