Sand-storms, once the terror of the town, were thus entirely prevented.
We have now laws for the protection of forests, and it has been suggested that government might, with equal wisdom, concern itself in the preservation of those grasses which hold together mud-flats and sandy shores.
For if such vegetable friends are wantonly removed, or are allowed to perish, valuable tracts of ground are buried under sand, or are altogether washed away, and harbors are rendered unsafe by accumulating shoals and bars of sand or mud, brought from other shores.
Some species of grass, in the course of many summers, convert marshes and half-submerged shores into firm land, and hence have been called "Nature's most valuable colonists".
They hold territory which has been wrested from the waters, and which, but for them, would speedily be retaken.
Thus they fix, if they do not change, the bounds of land and sea, and help to make geography for the boys and girls of coming generations.
To the evolutionary botanist the grasses are peculiarly interesting, for while many of their characteristics show the highest possible adaptation to the conditions of their lives, their flowers are conspicuous instances of degeneration.
They have reached, it seems, the last stage in a strange, eventful history. It is surmised that the first flowers ever born into the young world had stamens only, or a pistil only, as the case might be, had neither calyx nor corolla, and were windfertilized. The cone-bearing trees have blossoms which still adhere to these most ancient of all floral customs.
Later came the insect-fertilized flowers, with pretty corollas developed especially to charm their winged friends.
The grasses, in their present form, seem the latest flowers of all. They have reached a third condition, and after acquiring calyx and corolla to please insects, have abandoned these little messengers, - or been abandoned by them, - and have reverted to the primitive ancestral habit of dependence upon the wind.
Though the wind and the grasses take opposite sides in the contest between earth and sea, they are, on the whole, close friends. For the wind is not only the agent for the cross-fertilization of the grasses. He is the master-artificer who has moulded and fashioned them in every part, from root to flower.
If we pick a spear of "red-top" we find that its stem is hollow. The hollow stems of the grasses, like those of the dandelion, have the utmost strength obtainable with economy of material, and both strength and economy are needed in the structure of a stalk which must uphold, in the wind-swept fields, a proportionately large and heavy mass of bloom.
Fine whitish ribs run all down the length of the stem. These are woody and give it strength, and further re-enforcements are lent by the bases of the leaves, which are wrapped around the stem, so as to enclose it in a series of sheaths.
Each of these sheaths has an opening all down its length, and is welded to the stem by its base only, and just at the point of junction the stem is solid and swells into a knot (Fig. 38).
These knots or "modes," and the clasping leaf-bases also, are closest together near the ground.
Fig. 38. - Stems of the rye, showing the knots or "nodes".
(From the Vegetable World).
And the lower part of the grass-stem, which Nature thus reenforces, is just the portion subjected to the greatest strains when winds sway the head of blossom above.
The Indian corn, the giant among native grasses, with its large leaves and long slender stalk, seems peculiarly likely to fall a victim to the wind. And its fibro-vascular bundles, which are water and food conduits, might, one would think, be squeezed or crushed by the swaying of the breeze-rocked stem. A beautiful provision is made against either of these mischances.
Each bundle, in the first place, is invested by a strong, tough bundle-sheath. And being thus well protected individually, the bundles are used, collectively, as a means to reenforce the stem. For the course of each from the ground to the leaf is a long arch, curving outward. To each bundle with its sheath acts as a strut, and if the bundles interweave, as they do most beautifully, in some grasses and rushes they resemble the network of girders in an iron bridge.
A like adaptation enables the palmetto to support its heavy crown, despite the winds which blow so lustily in southern latitudes.
The gales which bend but do not snap the grass-stalk pass harmlessly over the long, narrow leaves, which have taken the form of pennants to meet a like necessity. For both grass-blade and yacht-pennant must expose the largest possible area to the light, and yet present no broad surface to be torn by winds.
These narrow leaves are born one by one along the hollow stem which botanists call a haulm. They are traversed by straight veins, which run lengthwise, almost parallel to one another. At the point where the leaf or "blade" bends away from its sheathing-base there is a little whitish, semi-transparent scale - the ligule or "shoe-latchet" (Fig- 39).
While "a grass" is speedily recognized by the merest tyro, the trained botanist is sometimes puzzled" in the effort to identify his particular grass, and to differentiate it from near relations, which resemble it as confusingly as Dromio of Ephesus resembled Dromio of Syracuse. Under such circumstances the ligule sometimes gives the clue, for in one species it may be chopped off abruptly, in another drawn out into a delicate point, and in a third cut into a fringe.
Its purpose in the plant's domestic economy is not evident.
As grass-flowers send their pollen abroad only by the wind, they have no need to lure insect messengers, and hence have no striking colors, and, in most cases, no perfume. They are generally very small, and are massed together in compact groups, which live in close propinquity to other groups, forming large floral communities.
Fig. 39. - Ligula of millet-grass.
(From the Vegetable World).