DISEASES OF GREENHOUSE PLANTS. 325 



tions of the leaves to take on a brown color. The 

 spores of the fungus are developed on the mycelium, 

 just beneath the cuticle, and, as this finally bursts and 

 rolls hack, they appear as at B. When magnified 500 

 diameters, the spores are seen to be two-celled (B) and 

 oblong in shape. If they fall upon 

 a damp rose leaf they will germinate 

 and cause another "spot" to form. 

 For the destruction of this fungus, 

 a perfect remedy is found in Bor- 

 deaux mixture, except for its giving 

 the plants a whitewashed appear- 

 ance. The copper carbonate solu- fig. 113. black spot, 

 tion is nearly as effectual and does Section ma « Illfled - 

 not have this fault. Evaporated sulphur will also keep 

 the disease in check. As in most other cases, prevention 

 will be found the best cure, and to effect this have the 

 beds well drained, avoid over-watering and maintain a 

 regular temperature of from 56 to GO degrees, according 

 to the requirements of the variety. 



powdery mildew of the rose (Sphmrotheca pannosa.) 



This common disease of the rose appears as a mealy 

 or powdery covering upon the young leaves, and if the 

 attack is severe they become twisted and distorted, and 

 the disease even affects the stems. It develops rapidly 

 upon the young leaves, its mycelium forming a fine cob- 

 web from which the spore-bearing stalks are sent up. 

 These stalks or hvphae become constricted and break up 

 into oval bodies — the spores, which are so numerous as to 

 form a fine powder upon the leaves, whence the name of 

 the fungus. This disease has another form of repro- 

 duction, the spores of which are formed in the fall and 

 arc designed to carry the disease 'through the winter. 

 The spores are in sacs, which are themselves enclosed in 

 a thick sac known as a theca. The winter spore cover- 



