Hold-Over Blight in the Pear 
7 
Table No. 2 gives the summary of the results of the two years’ ob¬ 
servations. 
Summary of Hold-Over Blight Determinations. 
1909-1911. 
(Table No. 2.) 
Date of Col¬ 
lection 
Date of Ex¬ 
amination 
No. of Twigs 
Examined 
No. containing 
living B. 
amylovorus 
Per cent con¬ 
taining living B. 
amylovorus 
Feb. 28, 1910 
Mar. 4, 1910. 
21 
7 
33.33 
Jan. 26, 27. 1911 
Feb. 4, 1911. 
28 
6 
21.43 
April 2, 4, 1911 
Apr. 21, 22, 1911 
34 
8 
23.53 
Total number twigs examined, 83. 
Total number twigs containing living B,. amylovorus, 21. 
Total per cent twigs containing living B. amylovorus,, 25.3. 
Closely related to the question in hand, is the persistence of the 
blight organism in the pruned twigs. We have always advocated and 
insisted upon the prompt collection and early destruction of this mater¬ 
ial because of the supposed danger of the disease being carried to the 
healthy parts of the tree. Through the courtesy of Prof. H. R. Fulton 
of the Pennsylvania Experiment Station, I am permitted to give here 
the results of his recent investigation along this line. While his work 
has been carried on in Pennsylvania, it is only reasonable to believe 
that, here again, the dry climate of Colorado would be even more severe 
upon the bacteria than the moist conditions which prevail in the East. 
“Twigs in which the blight bacillus seemed to be actively spread¬ 
ing were selected. These were cut in the ordinary way, and allowed to 
lie on the ground in thick clover and grass sod during the process 
of each test. The indication of viability of the organism in each in¬ 
stance was taken to be the inducement of characteristic blighting of 
succulent twig growth of apple, following its inoculation with bits of 
inner bark tissue from the tested twigs. These bits of bark were 
removed with sterilized instruments from three points in the region 
most recently invaded by the bacteria. Thev were introduced separately 
under the young bark of the rapidly growing twigs; and the incisions 
were covered with paraffin. Such a test was made first of all on the 
day the tested twigs were cut, in order to be sure of the viability of the 
organism at the outset. Subsequent tests to determine the time of its 
persistence were made in the same way after three days, five days, 
seven days, and in a few instances after a longer period.” 
“Out of a total of 35 twigs containing viable Bacillus amylovorus 
when cut, thirty-one twigs, or about 9-I0 did not contain living bac¬ 
teria at the end of a week; and most of these became inactive in three 
to five days. The death of Bacillus amylovorus in the twigs was rather 
uniform in the different tests, and there was not apparent such differ- 
