9 



we would leave the stump affected with the bacteria for a con- 

 siderable distance; and these would continue to multiply and 

 spread, and shortly the disease would again make itself man- 

 ifest. It is essential then in cutting off the blighted portion 

 of a tree, to cut far below the portion that looks diseased, 

 say from one to three feet according to the size of the limb. 

 It is also safer to cut off the dieased portion just as soon as 

 it appears, and before it has had time to spread to any con- 

 siderable extent. 



In the Fall the leaves that are diseased, as well as the unaf- 

 fected ones, fall to the ground. Here they decompose and 

 the bacteria are set free, for they do not decay, and are again 

 carried to other localities. In this manner the disease is 

 spread from one tree to another and from one field or local- 

 ity to another, and thus it is that the blight has and is 

 spreading all over our country. It is then readily under- 

 stood why it is that, if one neglect to attend to his fruit 

 trees, the blight will ultimately reach those of his neighbors. 



During the past summer I made pure cultures of the bac- 

 teria causing the blight in the pear, quince, apple, and a con- 

 iferous tree. These were made in nutrient gelatine by the 

 usual methjd of plate and tube culture. In this way the 

 bacteria from each kind of diseased tree were grown in sepa- 

 rate tubes of gelatine in which they fed and multiplied, and 

 thus were obtained a large number of individuals of each 

 special kind of bacteria, each tube containing but one kind 

 or species. 



Some of the bacteria from the tube containing the ones 

 obtained from the pear tree blight were then inoculated into 

 the healthy leaves of a pear tree by the use of a sterilized 

 needle dipped into the culture, and then pricked through 

 the epidermis of the leaf. Many leaves were thus inocula- 

 ted in different localities and on different trees, and each in- 

 oculated part labeled. In five days every leaf thus inocula- 

 ted had taken the disease blight, thus proving that these 

 special bacteria were the cause of the disease. 



