trunks.

The cordon can be reestablished in this case by allowing a vigorous
sucker to develop one year from which to form a new trunk the next.
The following year the old trunk is removed entirely. An objection to
this method is that it makes very large wounds in the most vital part
of the vine--the base of the trunk.

Figure 27 is a photograph of a four-year-old Colombar vine,
illustrating the unilateral, horizontal cordon system. It consists of
a trunk about seven feet long, supported horizontally by a wire two
feet from the ground. Arms and spurs are arranged along the whole
horizontal part of the trunk.

[Illustration: FIG. 27. Unilateral horizontal cordon with fruit
spurs.]

This system accomplishes the same objects as the vertical cordon. It
allows a large development of the vine and numerous fruit spurs
without crowding. It is superior to the vertical cordon in the
distribution of the fruit, which is all exposed to approximately the
same conditions owing to the uniform distance from the ground of the
fruit spurs. All parts of the trunk producing an annual growth of wood
and fruit are equally exposed to light and the tendency of the growth
to occur principally at the part of the trunk farthest removed from
the root is counteracted by the horizontal position. There is not the
same difficulty therefore in maintaining this form of vine permanently
that there is with the vertical cordon.

This system should not be used for small weak vines, whether the
weakness is a characteristic of the variety or due to the nature of
the soil. It is suited only to very vigorous varieties such as
Emperor, Almeria, and the Persian grapes when growing far apart in
rich, moist soil.

_Periods of development._

The first year in the life of a vine is devoted to developing a
vigorous root system; the next two or three years to building up a
shapely trunk and head, and a like period to forming the full
complement of arms. At the end of from five to nine years the
framework of the vine is complete and should undergo no particular
change of shape except a gradual thickening of trunk and arms.

There are, therefore, several periods in the life of the vine with
varying objects, and the methods of pruning must vary accordingly.
These periods do not correspond exactly to periods of time, so it may
be misleading to speak of pruning a two-year-old or a three-year-old
vine. One vine under certain conditions will reach the same stage of