212 ANNUAL REPORT. 



1880 he began more exhaustive researches and found that bacteria 

 was certainly the cause. Besides microscopic studies he made prac- 

 tical experiments. His plan was to take a little piece of bark that 

 was diseased and put it in a healthy tree and then watched it and after 

 a few days, a week or more, the healthy tree would become diseased 

 and begin to blight. Then he used another mode of experimenting. 

 He took a little of the fluid from diseased bark on an inoculating 

 needle and introduced that into the bark of a healthy tree. This pro- 

 duced the disease just as before. He not only inoculated the pear 

 trees from pear trees but also pear trees from diseased apple trees. 



He found that fifty -four per cent of the pear trees inoculated from 

 diseased apple trees took the disease, and in the case of pears inocu- 

 lated from pear trees seventy-two per cent. That shows very plainly 

 that the disease is identical in the two trees; it is the same in the 

 apple tree as in pears. 



He also inoculated apple trees, but the experiments on the apples 

 were not quite so strong; the disease didn't work quite so freely. The 

 apple trees inoculated from diseased pear trees took the disease in only 

 thirty per cent. In cases of the inoculation of apple trees he also 

 found that the progress of the disease was very much slower than 

 ordinarily supposed. He found that it did not start very rapidly; that 

 it was always slow; he found that it progressed an inch or so in the 

 stem up and down before it became noticeable and the leaves he found 

 did not turn black until a week or so after the disease had spread in 

 the bark. At first the color of the bark is only slightly changed; it 

 becomes black gradually, and it is only after the disease has been there 

 for some time that it is noticed at all. 



Mr. Whipple. Is that the Fire Blight you are describiug? 



Prof. Seymour. Yes, sir. 



Mr. Whipple. I have seen cases of Fire Blight when the first 

 appearance on the leaves, the circle affected being probably one-six- 

 teenth of an inch through. It looks as if it was scalded by throwing 

 hot water on the leaves and similar to that made by a drop of hot 

 water on the leaves of the trees, and probably the next day the leaves 

 would be all white. 



Prof. Seymour. Probably that is the beginning of the blackening 

 of the leaf observable. Probably the stem had been diseased before. 



Mr. Whipple. It is possible that such was the case, but I couldn't 

 discover any trace of it before. 



Prof. Seymour. This change is very slight at first. 



