The embryo nuts of the walnut, butternut, hickory, and beech, and the baby-acorns, appear on this year's new wood. The buds from which they have issued tipped the branches and contained, besides the pistillate flowers, a few of this year's tender leaves. The staminate flowers in all these trees issue from other buds, which grow lower on the boughs, on the old wood of last year.
But in all these trees we notice that the pendulous chains of stamens are more numerous on the upper branches and the pistil-bearing flowers grow more plentifully on the lower boughs. So the swing of the tree-tops in spring winds helps to shake the pollen out of the stamens, and the natural falling of the golden grains helps them to find their way to the waiting pistils.
The seedlings of these trees may have but one plant-parent apiece, and every healthy and mature tree of these species yields seed.
The poplars, as we have seen, conduct their affairs after a different fashion, and so do the willows, their nearest of kin. They bear stamens on one tree, and pistils on another. Each seedling-poplar or willow has had two tree-parents, and only certain individuals among the poplars and willows yield seed.
But some spring-flowering trees are apparently in a curious state of indecision and transition. Their habits are described by the technical botanist as "monceciously" or "diceciously" polygamous.
Sometimes their blossoms contain both stamens and pistils, sometimes they have only stamens and devote all their energies to the production of pollen, and sometimes they have only a pistil or pistils, and attempt nothing else except the perfecting of their own seed.
The perfect blossoms which bear both stamens and pistils may live in a household of staminate brother-flowers, or in a household of pistillate sister-flowers, or all three sorts of blossoms may grow together on one tree.
The red maple and the elm among early-flowering trees, and the holly, prickly-ash, and hackberry among the later trees, are thus unsystematic in their mode of conducting their affairs.
Their seedlings are born by the crossing of two flowers, or by the crossing of two trees, as circumstances may determine.
The seedling born of two flowers has a double advantage over the one which springs from a seed set by aid of pollen from the flower in which it grew. The offspring of two flower-parents is the stronger, and also the readier to accommodate itself to change in its circumstances and surroundings. It is therefore likely to live to maturity, and to bear many flowers, which will take after their "forbears" in a decided inclination to produce pollen in one blossom and seeds in another.
The seedling born of two plant-parents is even stronger and more adaptable than the one born of two flower-parents, and in the struggle for existence it is the likeliest of the three to survive. And its plant-children will follow the parental habit of setting seed by aid of pollen brought from another plant. So age by age the "dioecious" flowers have been separating their stamens and pistils more and more widely, and if the world lasts long enough the elms and red maples may reach the condition of the willows and poplars, with all the stamens borne on one tree, and all the pistils on another.
In Nature's school, elms and red maples seem to occupy an intermediate class with the walnuts and hickories below them, and the willows and poplars above.
The white-ash trees, which blossom in latter March or early April, are somewhat unsettled in their habits. Like the elms, they use both breezes and insects as pollen-carriers, and they have generally, but not entirely, adopted that plan of bearing stamens and pistils in separate flowers, which has become a fixed rule among the poplars.
The staminate flower-buds of the ash are very noticeable in earliest spring, when they are inkyblack, as Tennyson, that close observer of Nature, knew, for beautiful Judith in his "Gardener's Daughter" had hair "blacker than ash-buds in the front of March" (Fig. 12).
Under the purplish-black wrappings which enclose these spring parcels, there is brown wool, which has protected the bud's contents from wintry blasts, and under this blanketing we shall find stamens innumerable, but, as a rule, stamens only. These are minute at first, but they begin to stretch as soon as the bursting of the black case sets them free, and soon the stamen cluster becomes a conspicuous greenish-purple plume, branching freely, and composed of many long anthers on slender filaments. Towards the end of April these stamen-plumes fall, having shed all their pollen, and on the trees which have borne them seeds are not to be expected. For the pistils of most of the ashes grow on separate trees, in green, branching bunches, and by the time the leaves unfold each pistil will have developed into a winged fruit.
But the April aspect of the common or "white" ash hints to us that once upon a time ash-trees bore both stamens and fruits. For here and there on the boughs of this species a pistil can be found standing between two stamens. The modest trio attract no attention, by color, petals, or fragrance. Yet the technical botanist calls the little group "a perfect flower," and the evolutionary botanist sees in it an indication that once all ash-flowers contained both stamens and pistil and each tree was sufficient to itself.
Fig. 12. - Buds of the ash. (From the Vegetable World).
Fig. 13. - Perfect (a), staminate (b), and pistillate (c) flowers of the European ash (Fraxinus excelsior}. (All magnified).
The European ash, frequently cultivated in parks and gardens, is an individualist even to this day. Parted from all its kind by leagues of sea, like Crusoe on his island, it could take entire charge of its own affairs and carry them to a successful conclusion. The stamens and pistils are borne always on the same tree, and often in the same flower (Fig. 13).
But in all our native species, except the white ash, the future of the race depends upon the mutual helpfulness of the present generation. The stamen-bearing trees, which yield no seed, exist entirely for the benefit of the family. And the pistil-bearing trees, which are the hope of the race, cannot accomplish their task without help from their neighbors. The trees are learning cooperation, just as individuals do in a society which is emerging from savagery toward civilization.