24 MASSACHUSETTS HORTICULTURAL SOCIETY. 



contrast with that causing the Black Spot. Because superficial in 

 its manner of feeding upon its host this mildew can spread rapidly 

 over the rose leaves and quickly become manifest. 



There is another rose mildew (Peronosjyora sparsa Berk.) 

 which differs in many ways from the one last mentioned. It is 

 deeply seated, in that its fine filaments penetrate through all 

 portions of the leaf and afterwards produce upon the surface a 

 fine growth that has suggested the common name of Downy Mil- 

 dew for this fungous parasite. This mildew is closely related to 

 the ones upon the grape, the onion, the greenhouse lettuce, and 

 several other of the destructive downy mildews. 



As we pass along through the rose house some plants are seen to 

 be nearly defoliated. An inspection of the canes will show that 

 they are covered with small pimples, each one of which abounds 

 in spores. These microscopic spores ooze from the pimples or 

 small rifts in the epidermis of the cane and germinate quickly and 

 spread the trouble. This is the Rose Anthracnose {Gloeosporium 

 rosce Hals.) and is not distantly related to several of the worst 

 diseases of other cultivated plants. Thus Gloeosporium fnicti- 

 gemium Berk., is a widespread fungous trouble, causing bitter or 

 ripe rot in apples, grapes, and other fruits. The somewhat fatal 

 anthracnose of the raspberry {Gloeosporium venetum Speg.) is 

 another near relative of the trouble in hand. The rose plant is 

 most likely attacked through its young parts by the spores of the 

 anthracnose falling upon the leaves or succulent canes and, if the 

 latter, it may girdle the stem and thereby kill it. A plant thus 

 infested by the anthracnose may send up new canes from near the 

 base of the stem, which in turn are likely to bear pale sickly 

 foliage and finally to be destroyed by the fungus that in this 

 instance may spread to it directly from the old stem. This is one 

 of the most contagious of the fungous diseases of the rose. 



Some of the plants in the rose house have foliage that 'is badly 

 marked with gray, irregular, often quite small spots. If these 

 spots are looked at closely — and a hand lens will assist greatly — 

 they are seen dotted over with minute black specks, the spore- 

 bearing organs of SpJuerella rosigena P211., Fig. 1, b. In order that 

 this trouble may have a common name and to avoid the word spot 

 and any confusion with Black Spot the expression Rose Leaf Blight 

 is proposed. 



Before we leave the roses, and in answer to a question that has 

 already been asked, I may say that the peculiar discoloration of 



