=Edema.=--Under certain conditions plants in greenhouses or even in the open field, may absorb water through the roots faster than it can be transpired through the leaves, with the result that dropsical swellings or blisters occur on the leaves and more succulent stems. There is also a deformation of the foliage, much like the leaf-curl produced by over-feeding. This trouble, known as edema, occurs when the soil is warmer than the air, or during periods of moist, warm, cloudy weather, which checks transpiration. The grower should cease pruning, and withhold water, and in the field cultivate deeply. In the greenhouse, adequate ventilation should be given, keeping the house dry rather than moist. =Mosaic disease.=--The tomato is occasionally subject to a trouble allied to the mosaic disease of tobacco. It is characterized by a variegation of the leaves into light and dark green areas, usually accompanied by distortion and reduction in size. In severe cases a whole field may become worthless. While the nature of this malady is not fully understood, it is known to be due to a disordered nutrition of the young leaf-cells. It can be produced by severe pruning or by mutilation of the roots in transplanting, both of which should be carefully avoided. It is more likely to occur in seedlings that have made a soft, rapid growth on account of an excess of nitrogenous fertilizer or too high temperature. Close, clayey soils, on account of their poor physical condition, also favor the development of the disease after transplanting. =Western blight (Yellows).=--In the North Pacific and Rocky Mountain states, serious losses are annually caused by a disease apparently unlike any eastern trouble. It is marked by a gradual yellowing of the foliage and fruit. Development is checked, the leaves curl upward and the plant dies without wilting. The nature and cause of this disease is as yet unknown. It appears to be worst on new land. Experiments that have been made indicate that in older cultivated fields thorough preparation of the soil, manuring and cultivation, combined with care in transplanting to avoid injuring the roots and checking growth, will greatly restrict the spread of this blight. DISEASES CAUSED BY PARASITES There are several fungous parasites of tomatoes, which, for the readers convenience, may be briefly mentioned and the treatment of all discussed together. The first three are indeed somewhat difficult to tell apart without a microscope, as they produce a similar effect on the leaves and all yield to the same treatment--thorough spraying with Bordeaux mixture. =Leaf spot= (_Septoria lycopersici_ Speg.) has been widely prevalent and injurious during recent years. It produces small, roundish dark-brown spots on leaves and stems. The lower leaves are attacked first and gradually curl up, die and fall off. The vitality of the plant is reduced and it is only kept alive by the young leaves formed at the top.