her bacteria away from your trees you must see to it that all the
trees in the neighborhood of your orchard are kept free from mischievous
enemies. If harmful bacteria exist in near-by trees, insects will carry
them to your orchard. You must therefore watch all the relatives of the
pear; namely, the apple, hawthorn, crab, quince, and mountain ash, for
any of these trees may harbor the germs.

[Illustration: FIG. 119. A RESISTANT VARIETY OF SEA ISLAND COTTON
All the other plants in this field died. This one row lived because it
could resist the cotton wilt]

When any tree shows blight, every diseased twig on it must be cut off
and burned in order to kill the germs, and you must cut low enough on
the twig to get all the bacteria. It is best to cut a foot below the
blackened portion. If by chance your knife should cut into wood
containing the living germs, and then you should cut into healthy wood
with the same knife, you yourself would spread the disease. It is
therefore best after each cutting to dip your knife into a solution of
carbolic acid. This will kill all bacteria clinging to the knife-blade.
The surest time to do complete trimming is after the leaves fall in the
autumn, as diseased twigs are most easily recognized at that time, but
the orchard should be carefully watched in the spring also. If a large
limb shows the blight, it is perhaps best to cut the tree entirely down.
There is little hope for such a tree.

A large pear-grower once said that no man with a sharp knife need fear
the fire-blight. Yet our country loses greatly by this disease each
year.

[Illustration: FIG. 120. FIRE-BLIGHT BACTERIA
Magnified]

It may be added that winter pruning tends to make the tree form much new
wood and thus favors the disease. Rich soil and fertilizers make it much
easier in a similar way for the tree to become a prey to blight.

=EXERCISE=

Ask your teacher to show you a case of fire-blight on a pear or
apple tree. Can you distinguish between healthy and diseased wood?
Cut the twig open lengthwise and see how deep into the wood and how
far down the stem the disease extends. Can you tell surely from the
outside how far the twig is diseased? Can you find any twig that
does not show a distinct line of separation between diseased and
healthy wood? If so, the bacteria are still living in the cambium.
Cut out a small bit of the diseased portion and insert it under the