DISEASES OF FLOWERING PLANTS 209 



214. Preventives. Careful attention to watering and ven- 

 tilation will, in a measure, prevent an attack of black-spot. 

 Its presence outdoors usually indicates imperfect soil drain- 

 age. Black-spot is more prevalent on roses grown in heavier 

 soils than on those grown in light soils. The temperature of 

 the rose house should never drop below that required for the 

 varieties grown. The house should be kept entirely free of all 

 diseased leaves. 



215. Remedies. As soon as the disease becomes apparent, 

 pick off affected leaves and spray the plants with ammoniacal 

 copper carbonate. 



216. Leaf-spot on carnations. Classification: Sphaerioideae ; 

 Septoria dianthi Desm. Leaf-spot on carnations is very preva- 

 lent. It forms circular spots in the center of the leaves, or ir- 

 regular blotches on the margin, and it may attack the stems. 

 The center of the spot is gray-brown, while the margins have a 

 purplish tint. The leaf becomes deformed as its tissue shrinks, 

 and in a short time it turns yellow and dies. 



217. Microscopical nature. The mycelium enters the leaf 

 tissue through the stomata, spreads throughout the intercellular 

 spaces, absorbs the cell contents, and causes the characteristic 

 spotting. 



218. Reproduction. In a short time, pycnidia form in the 

 lighter portions of the spot. Pycnidia are black, flask-shaped 

 bodies, and^contain numberless, many-celled spores. In their 

 development, they rupture the epidermal cells and are liberated. 

 They are carried by air currents or by water in syringing, to 

 moist, healthy tissue, where they germinate quiekly and inoculate 

 other leaves. 



219. Ecology of leaf-spot. A close, humid atmosphere, and 

 too much water at the roots, are causes of leaf-spot. 



220. Preventives. To prevent leaf-spot give careful atten- 

 tion to temperature and atmospheric conditions in greenhouses, 

 and avoid over-watering. 



221. Remedies. The writer's attention was recently called 

 to a bed in which leaf-spot had gained a decided foothold. The 

 affected tissue was removed and burned ; careful attention was 

 given to watering; the temperature was kept comparatively 

 low, and the plants were sprayed with ammoniacal copper car- 

 bonate. The bed soon began to show a marked improvement, 

 and within two months the disease had entirely disappeared. 



222. Leaf-spot on chrysanthemums. Classification: Sphae- 

 rioideae, Septoria chrysanthemi Allesh. Leaf -spot on chrysanthe- 

 mums is quite general, and during seasons when the temperature 



