PLANT PATHOLOGY. 183 



2. Starvation, which is like that of animals, namely the lack 

 of a sufficient amount or kind of food. We know well enough 

 that to do well a domestic animal must have what we call a 

 "balanced ration," that is, one in which all the constituents 

 which are necessary to build up all parts of the body are present 

 in proper proportions. Now it is just so with a plant; it must 

 have a balanced ration also in order to do best, and if any of the 

 necessary food constituents are wanting it will suffer from 

 starvation. Fruit trees never starve for the food constituents 

 which come from the air, but they frequently suffer for want 

 of some which they ^should get from the soil. Now and then in 

 Nebraska a soil is deficient in nitrogen or phosphorous, or per- 

 haps iron, and the tree suffers. In other regions there may be 

 a deficiency of potash or lime, but this is rarely if ever the case 

 in Nebraska. 



3. Poisoning. This may be from gases in the air, which, 

 when absorbed by the leaves kill or injure their tissues. This 

 is not likely to occur in Nebraska, but it is common in manu- 

 facturing regions, especially near smelting works, coke ovens, 

 and like establishments which emit chemical fumes in consider- 

 able volumes. A much more common source of poisoning is 

 from the presence of harmful substances in the soil. Most 

 fruit trees can not endure the presence of appreciable quanti- 

 ties of common salt, and when this occurs in the soil in sufficient 

 amount the trees are slowly poisoned. So too, the presence of 

 "alkali" is harmful, as indeed is the case with many other soil 

 constituents. It must be borne in mind that lime, magnesia, 

 soda, iron, etc. etc. very dilute solutions of which plants need, or 

 at least are tolerant of, when in strong solutions become fatally 

 poisonous. In some cases the soil may be helped by the appli- 

 cation of some corrective, but for the most part it will pay the 

 fruit grower best to make selection of a soil which does not con- 

 tain any of these substances in poisonous quantities. 



4. Wounds. Attention has been repeatedly called to the in- 

 jurious effects of wounds on trees; in fact they are comparable 

 in their harmfulness to open wounds in animals. And just as 

 in animals a wound is a place through which harmful bacteria 

 may gain entrance to the body, so a wound in a tree allows 

 various kinds of injurious fungi to enter the inner tissues. 



