bark of a healthy, juicy twig within a few inches of its tip and
watch it from day to day. Does the tree catch the disease? This
experiment may prove to you how easily the disease spreads. If you
should see any drops like dew hanging from diseased twigs, touch a
little of this moisture to a healthy flower and watch for results.

Cut and burn all diseased twigs that you can find. Estimate the
damage done by fire-blight.

Farmers' bulletins on orchard enemies are published by the
Department of Agriculture, Washington, D.C., and can be had by
writing for them. They will help your father much in treating
fire-blight.

=Oat Smuts.= Let us go out into a near-by oat field and look for all the
blackened heads of grain that we can find. How many are there? To count
accurately let us select an area one foot square. We must look
carefully, for many of these blackened heads are so low that we shall
not see them at the first glance. You will be surprised to find as many
as thirty or forty heads in every hundred so blackened. These blackened
heads are due to a plant disease called _smut_.

[Illustration: FIG. 121. LOOSE SMUT OF OATS
The glumes at _a_ more nearly destroyed than the glumes at _b_]

When threshing-time comes you will notice a great quantity of black dust
coming from the grain as it passes through the machine. The air is full
of it. This black dust consists of the spores of a tiny fungous plant.
The fungous smut plant grows upon the oat plant, ripens its spores in
the head, and is ready to be thoroughly scattered among the grains of
the oats as they come from the threshing-machine.

These spores cling to the grain and at the next planting are ready to
attack the sprouting plantlet. A curious thing about the smut is that it
can gain a foothold only on very young oat plants; that is, on plants
about an inch long or of the age shown in Fig. 121.

When grain covered with smut spores is planted, the spores develop with
the sprouting seeds and are ready to attack the young plant as it breaks
through the seed-coat. You see, then, how important it is to have seed
grain free from smut. A substance has been found that will, without
injuring the seeds, kill all the smut spores clinging to the grain. This
substance is called _formalin_. Enough seed to plant a whole acre can be
treated with formalin at a cost of only a few cents. Such treatment
insures a full crop and clean