PLANT PATHOLOGY. 185 



are the most necessary organs of plants, especially of trees, and 

 yet the leaves are frequently destroyed so that the plant is 

 naked. Now the leaves are not the clothing of the tree, as is 

 supposed by some people, but they are much more like the 

 stomach, in which the food is prepared so that it can be used 

 by the plant. A tree without leaves is in practically the same 

 condition of an animal which has no stomach. Of course this is 

 a very crude comparison but it is true to this extent that both 

 leaf and stomach are necessary organs in the preparation and 

 digestion of food, on the one hand for the tree, and on the other 

 for the animal. When insects eat the leaves of a tree they de- 

 stroy to that extent the power of the plant to use the available 

 plant food, especially that derived from the air. And this is 

 the real nature of the injury of the tree when its leaves are lost 

 whether by insects, frost, hail or any other means. The result 

 is always the same, namely the loss of the power of utilizing 

 food. Such a condition is in fact one form of starvation, and 

 the final result so far as the plant is concerned is the same. 



Roots are sometimes destroyed by insects, moles or other 

 burrowing animals. The principal function of roots is to ab- 

 sorb water and food matters from the soil, so that the loss of 

 roots implies the loss of the power to absorb water and such 

 foods as are in the soil water. A tree whose roots have been 

 eaten off is in danger of dying from thirst as well as from starva- 

 tion. But trees suffer from the loss of their roots at the hands 

 of man himself, when he digs them out in such a way as to cut 

 off the roots close to the base of the trunk, A tree so mutilated 

 is in as pitable a condition as when it has suffered such a loss 

 through other means. The mere fact that the owner of the 

 tree has purposely cut off the roots does not help the poor tree. 

 It is quite as likely to die from thirst and starvation as though 

 the mutilation had been been done by rascally gophers or 

 moles. 



Some years the flowers of apple trees suddenly die before 

 the fruit has set. Here the disease is confined to the reproduc- 

 tive organs of the tree, and while the life of the tree itself is not 

 threatened, the crop of fruit is ruined. This disease is often 

 due to a form of blight, closely related if not identical with the 



