THE LIVING TREE 107
at the tip of the shoot: it is, doubtless, to some extent, protected
by the leaf stalk and the stem and is the least exposed position
on the stem.
A bud, then, is no more than a growing point surrounded
by a cluster of young leaves, each with its axilliary bud or at
least, with the possibility of a bud forming in its exit While
suitable for the growing season, such a bud would appear ill
suited to withstand the vicissitudes of the adverse season, from
which its delicate young parts would seem to require adequate
protection, and it is the general view that the tough overlapping
bud scales serve to protect the inner parts of the bud. Never-
theless, experiments by the Leeds school indicate that the tem-
perature inside the bud at night may be below that of its
surroundings. Other experiments by Professor Priestley and
his pupils involved removal of bud scales in November, thus
leaving the buds exposed to apparently harsh conditions in an
unprotected state : in some plants a surprising number of the
descaled buds still survived when examined in the following June.
These experiments certainly cast some doubt on the protective
value of the bud scales, but a good deal more information is
required before we can reject the widely held view that the bud
scales are protective. For example, it may be that under more
extreme conditions than those prevailing at Leeds, the scales
would have a heat insulating function or that under drier con-
ditions they may serve to prevent water loss. Moreover, it is well
known that some plants can stand freezing and subsequent
thawing, provided the changes in temperature are very gradual.
Even if the bud' scales do not prevent big fluctuations in the
temperature in the bud, they may at least act as lagging and prevent
too rapid a change. Until such time as Priestley's experiments
can be repeated on a wider scale it would be rash to assume that
the bud scales have no protective function: nevertheless,
these experiments give food for thought.
Bud scales are specially modified leaves or parts of leaves.
By dissecting winter buds it is often possible to trace a tran-
sition from the hard, robust bud scales to the delicate normal
leaf within the bud and it may be ascertained that in Sycamore
and Horse Chestnut, for examples, these scales correspond to
leaf bases, in Apple and Beech to stipules. In some trees
the winter buds appear less well protected : in the Common
Elder only the lower part of the bud is surrounded by bud scales
and the tips of the young, green foliage leaves are seen above,
while on the Wayfaring tree (Viburnum Lantana L.) there are no
bud scales and the outermost leaves of the bud, which in winter
are clad in a thick felt of hairs, will later expand into foliage
leaves.