THE LIVING TREE 111
in the Pedunculate Oak the leaves tend to be arranged approxi-
mately as rosettes on dwarf shoots, while in the Durmast Oak there
is a regular development of leaves on the long shoots. The more
regular arrangement in the latter tree produces a regular crown,
in the former there are gaps through which the sky may be seen—
a method by which the two species may often be differentiated.
In many plants the lower buds tend always to be more vigorous,
with the result that there is abundant basal growth and a single
tall bole is not produced : in this way the bush or shrub form
arises. This habit, of course, is often inherent in particular
species like Hawthorn and Blackthorn, but sometimes it results
from natural pruning. Thus Kihlmann describes Birches in
Lapland, which are always low, bushy plants because the buds
which project above the snow surface in winter are blasted by the
winter winds. A not dissimilar phenomenon is seen in many
trees growing in very exposed situations. Thus on the sea coast
trees often show a one-sided development with a much more
vigorous crown on the landward side, due to the adverse effects
of the prevailing salt-laden winds on the buds of the seaward side.
It will, of course, be apparent that all the buds which a tree
forms do not grow into branches : theoretically, the buds should
be more numerous than the leaves and in fact they are probably
nearly, if not quite, as numerous. The tangle which would
result if all those buds grew into shoots can scarcely be imagined.
A 10-year-old tree should have 19,683 leafy shoots if two lateral
buds had developed each year. Wiesner found, in fact, 238
shoots on a 10-year-old branch of Birch growing in the light
and 182 on a suppressed branch of the same age : moreover,
instead of the nine orders of branching theoretically possible,
he observed only five. Many of the buds which are developed
die as a result of competition and shading, but many remain
dormant and the figures just quoted illustrate in a striking
manner the enormous potentiality for branching in a tree.
Dormant buds may remain in a resting condition for years.
Those on the main stem of the young tree keep pace with the
increasing girth of the trunk and under suitable conditions come
into activity. This is well shown in the numerous shoots which
develop on Yew burrs and which have arisen from such dormant
buds. This type of bud is known as epicormic; other buds may
appear at any point on a stem, or sometimes even on roots.
They are formed particularly in the region of wounds, and it is
a common sight to see a mass of young shoots arising from a
wounded area of the trunk of the Common Elm, such as might
have been caused by a cartwheel. Such buds are termed
adventitious. In hedging, the vigorous cutting back stimulates
the development of dormant, epicormic buds, while cutting and