112 



THE PESTS OF CULTIVATED PLANTS 



of the plant. This is usually attributed to the fact that the 

 transpiration of water from the leaves is greater than the 

 absorption by the roots. A similar condition is also noted 

 when insects, such as the cutworms or the wireworms are 



eating the roots, thus 



cutting off the supply 

 of food and water and 

 causing the plant to turn 

 yellow. The yellowing 

 of plants also results from 

 the presence of gases, 

 either in the atmosphere 

 or in the soil. This trouble 

 is often found in cities 

 where leaks occur in the 

 gas mains, and it does 

 great damage to shade 

 trees and to ornamental 

 shrubs. Where the root 

 and the crown of the plant 

 are injured from gas it 

 results in the improper 

 physiological process go- 

 ing on, which in turn pre- 

 vents the transpiration of 

 water and the entire plant 

 is affected. 



The turning brown of 

 little patches on the leaf 

 with the dead portion 

 finally falling out, leaving 

 a small hole in the leaf, is 

 usually a clear symptom 

 of a fungous trouble. The 

 brown and the discolored areas on fruit, such as the rots 

 of the apple or the peach, are the outward signs of a fungous 

 disease. The abnormal swelling of certain portions of some 

 plants are indications that they are affected with some 

 organism. Two well-defined examples of abnormal swellings 



Fig. 51. — A diseased tomato plant. 



