348 GREENHOUSE MANAGEMENT. 



Another disease is the lettuce "Mildew." It is seldom 

 troublesome, except in dark houses, where the plants are 

 making little or no growth, on account of a cold, wet soil. 



A third trouble is "Leaf -burn," which causes the 

 edges of the leaves to turn brown. This is a common 

 trouble with the head varieties, and greatly reduces the 

 value of the crop. It is much less likely to appear in 

 the variety known as Grand Rapids than in most 

 other sorts. The usual cause of the trouble is growing 

 the lettuce at too high a temperature, especially if the 

 changes are sudden and extreme. A deficiency of water 

 in the soil, especially if the air is hot and dry, will also 

 lead to its appearance. In short, it may be attributed 

 to anything that will cause the water to be given off 

 from the tissues at the edges of the leaves faster than 

 it can be supplied to them. If the soil is light, the 

 roots will penetrate deeply and water will be supplied 

 much more readily than if it is heavy. 



DISEASES OF THE CUCUMBER AND MELON. 



Both of these vines are attacked by a downy mil- 

 dew (Plasmopara Cubensis, B. and C), which first shows 

 in the yellow color of the spots where the fungus is at 

 work, followed by the appearance of the frost-like 

 patches of spores on the underside of the leaves. In the 

 case of the cucumber, the spores are of a violet color. 

 This disease appears when the houses have been cold and 

 damp, and unless a radical change can at once be made, 

 the chance for a crop will soon be lost. The vines 

 should at once be treated with Bordeaux mixture, after 

 picking off all leaves that are affected and throwing out 

 the plants that have been much injured. 



CUCUMBER POWDERY MILDEW. 



The cucumber, when grown under glass, especially 

 if the air has been kept too dry, is sometimes attacked 

 with a fungus that is thought to be ErysipJie Cichora- 



