118 



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 atmos- 

 phere 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 going on, which 

 in turn prevents the 

 transpiration of water 

 and the entire plant is 

 affected. 



The turning brown of 

 little patchs on the leaf 

 with the dead portion 

 finally falling out, leav- 

 ing a small hole in the 

 leaf, is usually a clear symptom of 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. 



FIG. 52. A diseased tomato plant. 



