TOMATO DISEASES 133 



takes the hint and modifies his methods so as to per- 

 mit a more balanced growth. On the other hand, the 

 ill effects of over-feeding and pruning may reach a 

 point where the plant is seriously crippled. 



Edema. — Under certain conditions plants in green- 

 houses or even in the open field, may absorb w'ater 

 through the roots faster than it can be transpired 

 through the leaves, w-ith the result that dropsical swell- 

 ings 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 sub- 

 ject 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 mutila- 

 tion 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 ac- 

 count of an excess of nitrogenous fertilizer or too high 

 temperature. Close, clayey soils, on account of their 



