1184 | Pear Blight and its Cause. [ December, 
every evidence of having been arrested in the midst of rapid 
growth. The conviction was established that the germs enter 
the tree in spring through the moist glandular surfaces within 
the flower or the tender surfaces of expanding buds, but that the 
disease does not make sufficient progress to become conspicuous 
till the warm days of June or July. As the flowers drop and the 
branches cease extending less and less chance exists for the tree 
to take the disease. Insects may now and then transfer the 
germs, for two pears were found the present season filled with 
blight, in both cases showing the point of entrance, evidently a 
puncture made by an insect. It is only in some such exceptional 
way that the germs can gain admittance through the well pro- 
_ tected surface of fruit. 
If the germs pass from the air into the tree, in what manner 
do they get out into the air again at the proper time for the next 
season's attack ? Manifestly the bacteria within the tree are se- 
curely imprisoned by the bark, which as effectually prevents their 
escape as it does their entrance; and at any rate, in spring, the 
time for attack, there are few bacteria left alive in the tree. 
Limbs with tender tissues exude great numbers of germs during 
July and August, but so agglutinated that the air cannot dislodge 
them, until the rains have washed them to the ground and dissolv- 
ed the gum which binds them together. The query now presents 
itself whether the germs may not be able to thrive outside the 
tree. To test this, cultures were tried in various media, and it 
was found that infusions of hay, corn meal, starch and various 
other vegetable substances make a nutritive fluid in which the . 
_ blight bacteria flourished in varying degrees, no matter whether 
the solutions were acid, alkaline or neutral. When transferred 
from the culture fluid to the tissues of the tree, the usual form of 
blight follows. This plainly indicates that the germs washed 
from the tree by rain may find congenial nidus among vegetable 
— refuse, thrive and multiply, pass the winter, for cold does not 
i injure them, even pass an unfavorable year or two, and at times 
: ; swept into the air be brought by gentle rains or an arrest- 
of dew into contact with the delicate surfaces of expand- 
ot or flower and infection be secured. 
hay g shown the | progress of the disease to be coordinat- 
Le ent of germs and traced the life cycle of the 
still persons who do not believe that 
