110 THE ESSEX NATURALIST
few years or remain as a stump bearing a few buds or again, as in
Sloe, the dwarf shoot often loses its apical bud, its tip becoming
hard and forming a thorn. Dwarf shoots commonly bear the
flowers and in general lie nearer the base of the year's growth:
possibly this position, with its inevitable shading, is less favourable
for growth, hence the stunting ; but it seems more probable that
we are dealing with an inherent factor and one which is not
glibly explained merely in terms of shading and nutrition.
The forms of trees are numerous. Where there is strict
monopodial growth, as in the Spruce, a tree of very regular
conical form is produced, for growth of the main trunk continues
year after year from the same growing point and similarly the
growing point at the tip of every branch is responsible for its
extension growth throughout life; and since the older branches
are lowest on the trunk they will grow longest and thus will be
produced the regular conical form so familiar in the Christmas
tree. Strangest form of all, perhaps, in a tree with monopodial
growth is that of a variety of the Common Spruce (Picea Abies
var. monstrosa (Loud.) Rehd.), in which lateral branching is
suppressed, the tree consisting of a single trunk with stiff leaves.
The monopodial habit is often lost later owing to lateral
branches growing more vigorously than the leading shoot and
the subsequent suppression of the leader. In Silver Fir (Abies
alba) the Christmas tree habit is retained for many years, but
in old trees the leader dies and the upper lateral branches grow
vigorously, giving a tufted top, a habit aptly named by the
Germans the eagle's eyrie habit. Young Pines are likewise
monopodial, but later, with loss of the leading shoot, become
more or less flat topped—branching has become sympodial.
Most broad-leaved trees show the sympodial type of growth—
without a leading shoot. Concerning their shape, much depends
on the branches : they may diverge at a small angle with the main
trunk and give rise thus to the fastigiate habit so characteristic
of the Lombardy Poplar and the Cornish Elm : again the branches
while emerging at an acute angle, may later bend down, and in
extreme forms give rise to weeping trees such as occur in some
Willows, Elms and Ashes. Again, branching may lead to other
characteristically shaped crowns : the flattened shoot systems
of the Beech, borne on main branches which are first obliquely
erect and distally nearly horizontal, produce the stratified
appearance which characterises that tree. On the other hand,
more rounded crowns are produced by a spiral arrangement of
branches. Sometimes, the lower lateral branches grow much
more rapidly than the upper ones, so that most of the branches
reach the same height, producing the flat-topped crown seen in
many leguminous trees. Busgen and Munch point out that