8 
Colorado Experiment Station. 
ences in the persistenc as might have been expected from the difference 
in rapidity of drying of the twigs. There was indication of slightly 
longer persistence in the last two tests when lower temperature was a 
more conspicuous feature perhaps than increased moisture. Twigs that 
had been blighted for a longer period did not show any difference in 
persistence from those of shorter period, the test in each instance be¬ 
ing made from portions of the bark recently invaded. 
Incidentally it was noted that the dried distal parts of blighted 
twigs did not, as a rule contain viable blight bacteria. The extent of 
the zone containing them was not determined, but it evidently varied, 
and included in general the discolored bark that was apparently moist. 
The characteristic dried exudation made up of blight bacteria, was 
tested in several instances, and the bacteria in this seemed regularly to 
remain alive longer than in adjacent dried bark; and their persistence 
after the twigs were cut was two to four days longer than of bacteria 
in recently invaded bark of the same twig. 
When one considers the comparatively rapid death of blight bac¬ 
teria in cut twigs left on the ground, which these tests indicate, and the 
unlikelihood of any ready transfer of infective material from such a 
situation to living parts of orchard trees, one is inclined to question 
the necessity for rigid destruction of cut off twigs. It may, however, be 
well to defer final judgment until the effect of leaving such material 
on the ground, has been observed in actual orchard practice.” 
CONCLUSIONS. 
1. In the arid Western climate, the prevalence of Hold-over Blight 
in the small limbs and twigs of the pear has been underestimated. 
2. LTnder Colorado conditions, at least 20 per cent, of hold-over 
cankers on the small limbs and twigs contain virulent blight organisms 
at the time of blossoming. 
