INSECTS, DISEASES AND SPRAYING 53 



to the disease. Dr. B. D. Halsted has seen 

 the black spot upon a species of wild rose 

 (Rosa humilis), where it was causing the 

 leaves to become spotted and yellow. The 

 wild plant was growing but a short distance 

 from a neglected estate where garden roses 

 were badly spotted. 



The Actinonema, the fungus causing the 

 disease, belongs to a small genus, and some 

 of the species are parasites upon the bass- 

 wood, beach, ash, viburnum. The one upon 

 the rose is not found upon plants outside of 

 the genus Rosa, and there has its favourite 

 species and varieties. This is shown in a 

 remarkable manner with some of the cul- 

 tivated sorts grown side by side in the same 

 house. It is often very bad upon the Amer- 

 ican Beauty. 



The Rose Leaf Blight disfigures and injures 

 the rose leaves almost as badly as the black 

 spot. A thoroughly diseased leaflet has 

 large irregular blotches of grey colour sur- 

 rounded by a margin of dark purple. The 

 grey dead centre of the spot bears a number 

 of pimples or specks — more numerous and 

 conspicuous near the centre— and in these the 

 spores are produced, It is closely related to 



