The Night is Mother of the Day,
The Winter of the Spring; And ever upon old Decay,
The greenest mosses cling.
Behind the cloud the starlight lurks, Through showers the sunbeams fall;
For God, who loveth all his works, Has left His Hope with all. - Whittier.
When the "leaves have forsaken the trees and the forest is chilly and bare" it seems that the wandering botanist will find nothing there to interest or amuse him.
But botany, like evil doing, has all seasons for its own, and even when leaves and flowers are gone, there are still in the woodlands a few signs that the world's heart is beating still under its slumber-robe of snow.
Some humble plants go on growing, even at a season when one would suppose all vegetation to be benumbed with winter's icy breath.
In sheltered hollows, where the sunshine causes a little thawing now and then, we can always find a few green ferns. Lichens, which make their homes as far north as the Arctic circle, are not discouraged by the worst our January can do. Some mosses are green, still, under the snow, and on the trunks of many trees, even now, we may notice a green film which is caused by the growth of some tiny and humble cousins of the rich green "sea-lettuces" which float at the edges of tidal pools on rocky coasts.
Probably the very great-grandparents of these little land algae were seaweeds or fresh-water weeds, and the family love for coolness and shade is constant through all changes. For when the leaves are gone, and even subdued colors "tell" amid the general grayness of the woodlands, we see how persistently the land algae choose the north sides of the tree trunks. Lichens, too, love best to grow where the direct rays of the sun cannot reach them.
We look southward through the woods, and every tree from earth to branches is spotted or filmed, or shrouded with a close-clinging growth of sober but living green. We see the north sides of all the tree-trunks and they are covered with minute shade-loving plants.
But if we turn and look northwards through the woods the trunks appear bare. By this little bit of wood-lore Indian hunters used to "get their bearings" in the pathless forests.
Raising our eyes we notice the great beauty of the patterns which interlacing boughs and twigs trace against the sky. Each tree has its own beauty, for the form of the bare branches is almost as distinctive as that of the leaves, while bark is so characteristic that a hunter or a lumberman can often tell the name of a tree from its bark alone.
By time the dark days of November come the trees are all asleep and each is wrapped from its topmost twigs to its lowest roots in a slumber-robe of Nature's own weaving, a close tissue of cork-cells.
Though every plant of the field and every tree of the wood is entirely built of cells, these cells may differ widely from one another in shape, size, and use.
They may be filled or partly filled with colorless jelly, they may contain resin, tannin, mucilage, oil, or mineral crystals, or they may be empty. They may be many sided, or cylindrical, or spindle-shaped, or thread-like, and the thread-like ones may be straight or twisted or branched. Sometimes the cell walls are very thick, sometimes they are thin, and sometimes they are pitted or barred or ringed so that under the microscope they show patterns of great beauty.
A tiny sliver of wood may be made up of many kinds of cells, which are alike only in one respect - that the tree has had a use for them all.
Toward the centre of the trunk and larger branches lie the oldest cells, whose work is nearly or entirely done.
They form the "heart-wood" which, as every cabinetmaker knows, is darker in color and closer in texture than the younger "sap-wood " which surrounds it.
Outside the "sap-wood" there is in spring a layer of young growing cells which are building up new bark and new wood. In April we shall find this forming tissue lying just below the bark, between it and the wood.
But at this season no active growth is going forward, and no delicate new cells are forming and swelling between the tree and its bark.
In the bark itself, at varying depths according to the kind of tree, lie several layers of cork-cells.
In summer this cork undergarment covers all the tree except the tops of its tenderest twigs and the ends of its slenderest rootlets. Nature has taken care that the water sucked in by the roots shall not be evaporated and lost as it goes up through trunk and branches to the thirsty little shoots at top. So the year-old twigs have a tough skin, which is nothing more nor less than a thin sheet of cork, while older branches are encased by a thicker cork-covering, which lies, as a rule, below the surface. Be it thin or thick it is perfectly water-proof.
The peel of a potato is nothing more nor less than a layer of cork-cells, and, by observing the quickness with which pared potatoes "dry out," we realize how effective even a thin cork-covering can be in preventing the transpiration of vegetable moisture.
The life-giving juices of the tree can not get through the cork-layers of the bark to nourish the outermost tissues of the trunk and branches. So all these parts of the tree which lie outside the cork-layer dry up, shrivel, crack apart, and at last flake off and fall to the ground.
These dried and drying tissues may include cells of many sorts and sizes, which in their younger days served various uses in the tree's domestic economy. But now we speak of them all together as the "outer bark.'
The sheet of cork which is wrapped around a branch may lie near its surface or deep in its tissues.
And their various and sundry ways of wearing their union suits cause marked differences in the appearance of the trees even in winter, for the cracks which begin at the outer surface of trunk or bough will go " clear through" till they come to the cork sheet, wherever that may be.