108 THE ESSEX NATURALIST
Most buds are formed fairly early in the year prior to their
opening and they are in fact resting during the summer and
winter which precedes their unfolding. Much attention has
been given to discovering the causes of opening : it is not merely
due to a rise in temperature in spring, for there is a period during
which buds cannot be forced to open. In Lilac these young buds
can be made to expand up to the end of August, and from
November onward, but there is no known method by which
the buds can be made to open in September and October ; this
difference in behaviour appears to be related to chemical changes
which occur in the bud during its resting period. Frost appears
to hasten opening, perhaps because it converts the starch in
the buds into sugar, but the actual opening depends upon
warmth. The late opening of the winter buds in the spring of
1947 was doubtless due to the severe conditions which prevailed
in the early spring and the tardy arrival of higher temperatures.
When the buds do open in spring their leaves expand and
there is a period of rapid extension growth which may be of
relatively short duration. Thus in Beech extension growth
ceases before the end of June and a new winter bud is produced
ready for next year's increase in length. Horse Chestnut likewise
has a short period of extension growth, but in some plants,
like the rose and the willows, the shoots increase in length through-
out the growing season until growth is stopped by autumn frosts.
Where extension growth is of short duration a definite number of
leaves open each year ; they were formed in the previous year.
Lateral buds in Larch have been fully formed in May, while in
a Common Spruce bud the leaf primordia are all formed by winter;
it is thus in the summer prior to that in which the leaves appear
that it is determined how many leaves can be formed—presumably
depending upon weather conditions. Similarly, flower buds of
trees are formed in the year prior to that in which the flowers
appear, to give rise to fruit later in the year. It may thus be
safely asserted that the prevalent notion that the severity of a
coming winter may be gauged by the number of berries on the
trees during autumn is without a foundation of fact ; the amount
of fruit which will appear in the autumn is to a large extent
influenced by the weather during the summer of the previous
year.
Although we have referred to the early formation of winter
buds in some trees, extension growth for the year does not
necessarily cease at that time. In some trees, like the Oak,
and especially in young trees, the winter bud may break into
activity again in the later summer and there is a new period of
extension growth. Because this second period corresponds more
or less with Lammas time, i.e. the beginning of August, such new