518 XEW JEESEY AGRICULTUEAL COLLEGE 



the spread of the niildew. and a second form that matures slowly, 

 ]>erhaps requiring months for this, and remains over winter before 

 they start into growth. 



Expert rose-growers can detect the rose mildew in the greenhouse 

 possibly before it is at all apparent to the eye. There is a peculiar 

 odor to this group of fungi that is not met with elsewhere, and a 

 leaf badly affected with the summer form gives off -this odor so 

 strongly that, when it is held close to the nose, the diagnosis is 

 unquestioned. 



Several of our serious j^lant diseases l^elong among these mildews, 

 and in the following paragraphs they are considered somewhat at 

 length. 



Their Classification. — The kinds of powdery mildews are not nu- 

 merous. According to Salmon there are only forty-nine species and 

 eleven well-marked varieties known in all the world. The differences 

 between the kinds are chiefly microscopic, and belong mainly to the 

 penthicia and their contents. In other words, the mildews, as they 

 first appear from the germinating spore, usually in early summer, 

 are all very much alike, and a student of the subject does not feel 

 that the species or genus can l^e certainly determined without the 

 so-called "winter fruit."' The case is somewhat similar to the classi- 

 fication of apples or pears, peaches or blackberries, without their fruit. 

 The vegetative portion of the mildew corresponds to the stems and 

 leaves of the trees or shrubs, the summer spores to the many buds, 

 and with only these the kind cannot be definitely known. Some plants 

 bear quite generally mildews which fail to produce the winter spores, 

 and in all sucli instances it is uncertain what species of mildew is 

 present. An interesting case is the European grape mildew, which 

 was named Oidium Tucl-eri, by J. M. Berkeley, in England over a 

 half a century ago (1845). Since that time the mildew has 1:>een 

 very destructive to the grape industry throughout Etirope, Asia and 

 the United States, but not until 1892 were the penthicia found asso- 

 ciated with Odium Tucl-eri in the vineyards of France. In the mean- 

 time a mildew was found upon grape vines here in America that 

 produced the "winter fruit," but the question of the identity of the 

 xlmerican and European form was not generally admitted, and the 

 conclusion was only reached by finding both kinds of spores upon 

 the grape in the home of the Oidium. 



To bring the matter closer home, the writer has a matrimony vine 

 upon his house piazza, that mildews each late autumn, but after the 



