78 THE ESSEX NATURALIST.
The salient features of B. alba are:—Height 75 to So feet,
the thin branches, as they fray out, pendulous, young branches
with resinous peltate glands, hairs absent, leaf lamina acuminate,
doubly serrate, veins raised on upper surface, lateral lobes
of the bracts more or less falcate (Plate VIII. fig. 2), wing of fruit
twice or three times the diameter of the nutlets.
The chief points respecting B. pubescens are:—Rather less
in height than B. alba, young branches with hairs, often densely
pubescent, not infrequently with small rudimentary verrucosities,
leaf lamina not acuminate, irregularly serrate, veins raised on
the under surface, more or less hairy when young, often glabrous
or sub-glabrous later, wing of fruit as broad as or a little broader
than the nutlets.
The white birch has a deeply furrowed bark, but the depth
of the furrows, and the extension from the base of the trunk
upwards, vary considerably.
The birch is shallow rooted. Great numbers of slender roots
are found at very little depth below the surface of the soil and
should there be an accumulation of decaying leaves, at or near
the foot of the tree, numerous, thread-like rootlets, each infected
with mycorrhiza will be found ramifying throughout the decaying
mass.
Birches, owing to their shallow root-system, are considerably
damaged by heavy storms. At the present time there still
remain evidences of the damage done to these trees by the
great snowstorm of Sunday, 27 April 1919. It fell upon the
birches when they were in full spring foliage. Being heavily
weighted with snow, the shallow root-system proved quite
inadequate to withstand the severe strain. Some trees are now
growing out of the perpendicular, others that were brought
to the ground were soon afterwards stripped of their branches
(Plate VIII. fig. 1). The trunks of some still remain upon the
ground forming an excellent nidus for saprophytic fungi.
The groves of the High Beach—Epping plateau are, in some
localities, as close around the church of the former place, and at
Long Running, almost pure birch, while in others the wood is
of the type, oak-birch-heath association, with a large propor-
tion of birch. The association has not been invaded by Pinus
sylvestris although this tree was planted some forty years ago
at Piercing Hill.