1899.] PUBLIC DOCUMENT — No. 33. 161 



activity in transpiration takes place during sunshine. This 

 fact is frequently demonstrated by young cucumber plants 

 in tolerably good conditions of health, which not infrequently 

 show some indications of wilt in sunshine, though not enough 

 to cause any amount of harm. This is especially so when 

 they are forced too rapidly, and when the texture of the leaf 

 is not sufficiently developed. The temperature of the air 

 affects transpiration. A plant in an atmosphere saturated 

 with moisture will not exhale any watery vapor, provided 

 that the temperature of the plant is not higher than that of 

 the air ; but when the temperature of the air is high, and 

 the proportion of moisture small, transpiration is promoted. 

 Transpiration is further affected by the temperature of the 

 soil in which the roots are embedded. When the roots are 

 warmed, transpiration becomes more active, and conse- 

 quently there exists more root absorptive activity. The 

 nature of liquids which the roots absorb and the kind of soil 

 in which they grow also affect transpiration. Plants tran- 

 spire more when grown in sandy soil than when grown in 

 clay soil ; also when grown in acid soil than when grown in 

 alkaline soil. One per cent, solutions of potassium nitrate 

 and other salts diminish transpiration, and we have been 

 able to produce severe cases of the wilt by watering pots of 

 cucumber plants with a one per cent, solution of potassium 

 nitrate. 



The wilt, however, in the houses mentioned before was 

 not due to temperature or constituents of the soil, but was 

 brought about, as we have already inferred, by irrational 

 methods of treatment of the plants, and depends upon 

 other causes. In all probability, the cause of the wilt may 

 be attributed partially to the characteristic peculiarities of 

 the varieties of cucumbers grown, as most of the varieties 

 are Telegraph or Giant Pera. In many cases hybrid forms 

 are obtained by crossing these with the White Spine. These 

 varieties present a different appearance from the AVhite 

 Spine ; their stem and leaves appear to be small, and the 

 plants do not appear normally as green and rugged as the 

 White Spine. 



The methods of o^rowinj; cucumbers where the wilt occurs 



