86 THE CULTIVATION OF THE 



tagious diseases, like cholera, small-pox and diphtheria, 

 etc., and do not generally grow and increase in tissue 

 that is perfectly healthy. When the tissues become 

 weakened from any cause, the proper conditions are 

 produced, the germs found everywhere begin at once to 

 develope, taking up the food that would otherwise go to 

 the nourishment of the tree, and the result is the 

 destruction of the latter. 



Among the causes that may bring about this 

 weakened condition, are, first, a late, immature or soft 

 growth, which, upon exposure to severe cold, is so 

 injured that the very unstable elements of which the 

 tissue is composed, break up quickly, and fermentation 

 begins, or, in other words, a very rapid growth of the 

 bacterial cells, or germs, takes place. In some cases 

 the tree is killed very soon after warm weather sets in, 

 or, if less injured, decay goes on more gradually* 

 Another cause of weakness may be found in the exhaus- 

 tion of the soil, by the plant-food being all taken up by 

 the roots, which are gross-feeders, and fermentation may 

 result from the cells being in an inactive condition. 



Exhaustion of the plant may also result from over- 

 bearing, when the cells are not only exhausted, but the 

 plant-food of the soil is so reduced that the supply is 

 insufficient to keep up a healthy action. Perhaps the 

 greatest factor in the weakening of the tissue is the 

 peach-borer. This insect is so well known that I will 



