But the needles of pines, hemlocks, and firs shed the flakes from their curved and shining surfaces and allow them to fall through the feathery branches toward the ground. Snow occasionally gathers upon the trees in masses sufficient to form a beautiful contrast to their sombre green, but its hold on the slippery needles is so insecure that the least puff of wind suffices to dislodge it.
The broad-leaved evergreens, laurel, laurestinas, holly, bay, and live-oak are native to climates where snow seldom falls heavily, and never lies in unwieldy masses.
The little needle-shaped or scale-like leaves of northern evergreens make up in number what they lack in size.
But though the trees are evergreen their leaves are not. One by one they fade and fall, till, in the course of a few years the entire foliage has been shed. Thus the spruce drops all its needles in the course of six or seven years. The yew-leaves fall after they have weathered the gales of about eight winters, and the leaves of the silver-fir drop to the ground when they have reached the ripe old age of twelve years. The discoloration of ageing leaves is not noticed amid the general greenness of their surroundings, and the void made by their fall is soon filled by fresh individuals.
The larch in the North and the "bald-cypress" in the South have departed widely from the family custom of the cone-bearers. Like the broad-leaved trees they drop their foliage each autumn, and they appear in spring clothed in complete new suits of tender green.
The true evergreens which retain their needles throughout, assume a sombre tint with the coming of the first heavy frosts. This is because the chlorophyll-bodies which give the foliage its hue lose their vivid color in the autumn and change to a brownish-green.
The pines and hemlocks are most noticeable in winter, when there is no other green in the landscape and when they are contrasted with the snow; but in reality their color is more intense in summer. For in the first warm days of spring the chlorophyll bodies in the needle-shaped leaves resume their characteristic color, and with it their "activity of toil".
New-born pine-leaves issue in pairs, trios, or fives, from little brown buds, which are covered with delicate semi-transparent scales. These are regarded as altered "needles," just as the scales which protect the winter-buds of many broad-leaved trees are altered leaves.
The new needles of the white pine (Fig. 76) come into the world in fives. Those of the Jersey or scrub-pine are twins, and those of the pitch-pine grow in clusters of three. Each of our twenty-two native pines is faithful to some old family custom in this respect, so that if we count the needles issuing from the bud we have observed one of the characteristics by which we may determine its species.
Fig. 76. - Leaf cluster and bud scales of the white pine (Pinus strobus).
After the leaf-cluster is mature the little brown bud-scales which sheltered its youth drop away and fall. A slow, gentle shower of them drips earthward in the pine-woods all through the latter year, and adds largely to that soft, mouldering carpet which covers the ground beneath the trees.
In the balsam-fir and in the yew-tree each needle has its own guardian scale-leaf, and the foliage is distributed evenly over the surface of the bough (Fig. 77).
Within the needle-like leaves of the pines and their cousins there is no delicate network of branching-veins such as we see in the foliage of oaks and maples. Instead, there is one compact bundle of vessels and tubes, through which plant-fluids creep out toward the sunlight to be digested, and then back again to growing roots and shoots. This bundle lies at the very centre of the leaf, and is sheathed, and in a measure protected from cold by an enclosing tube of thick cells with corky walls. Outside this corky tube lies the green substance of the leaf, composed of delicate cells containing chlorophyll.
Fig. 77. - A spray of the balsam-fir (Abies balsamea).
This tissue, like the bundle of vessels, is guarded by Nature against frosts and winds, for outside the delicate green cells there is a tough encompassing layer, or, it may be, several layers, of fibrous cells with very thick walls. These strengthen the leaf, rendering it less liable to be broken by gales, and they also serve, in a measure, to protect the inner tissues from sudden changes of temperature and from the drying effect of high winds. Then, outside all, is the leaf-skin or epidermis, which is also thick and fibrous.
The stomata are distributed evenly over the surfaces of these needle-shaped leaves. They pierce through the epidermis, and through the fibrous tissue beneath it, to the delicate green cells which may have superfluous moisture to breathe away. But as the cone-bearers often live on stony ground and in wind-swept situations, it is desirable that their leaves shall not part too readily with their vegetable juices. So each stoma opens at the base of a depression in the leaf-surface, where it is somewhat sheltered from the direct sunlight.
Even in New England there are a number of birds which do not join the great southward migration, but stay to brave winter and rough weather. During latter autumn this remnant is reenforced by the arrival of birds from the North, to whom our latitudes are what Florida is to shivery people of elegant leisure. In the vicinity of Norfolk and of Cincinnati the bird-life of the leafless woods is almost as full and intense as that of the summer. But when the wind swoops down from the North, and deciduous trees afford no protection, the evergreens offer the birds a refuge in the time of trouble. Here they find both shelter and food, for after the "hips and the haws are all gone," and snow has covered the earth, a living can still be eked out, thanks to the juniper berries and the seeds of the cone-bearing trees.