8 



of the bacteria in consuming the tissues, or it may be as a 

 result of the chemical action of the waste products (pto- 

 maines) thrown off during the growth and metabolism of 

 the bacteria. Hence it is observed that there are many spe- 

 cies or kinds of bacteria; and they not only act differently 

 and produce different results and diseases, but each species 

 as a rule has its particular animal or plant or substance in 

 which it will grow and multiply and will not do so in any 

 other. 



The bacteria that cause the disease in fruit trees known as 

 blight are carried by the wind, or by insects in some cases, 

 from the soil to the buds or leaves of the trees. Here they 

 gain access to the interior of the leaves by means of the 

 stomata or minute openings in the epidermis of the leaf, of 

 which there are in some cases many thousand to a square 

 inch. Once on the tender buds or inside the leaves the bac- 

 teria find suitable food and conditions for their growth and 

 multiplication. They feed upon the tissues of the host 

 plant and destroy it, and as they increase in number, they 

 gradually come to infest the entire leaf, and finally the peti- 

 ole and the twig to the stem and other healthy parts. In 

 this way the disease once started in a single place in the 

 tree, will spread so as to include in time the entire limb or 

 even the entire tree. The disease works down towards the 

 trunk of the tree as well as in all other directions, and since 

 the tissues affected soon die, it follows that if the blight 

 start low down on a branch, it will necessarily kill the entire 

 branch beyond the diseased portion. 



The peculiar coloration of the blighted portion does not 

 in reality indicate the entire area affected, since the bacteria 

 are in many cases, especially in the stem, far below or down 

 the branch before the coloration appears there, the coloration 

 not being produced immediately upon the appearance of a 

 few bacteria. Hence in cutting off of a diseased limb it is not 

 sufficient to cut off the portion showing the coloration, since 



