Trans. S. E. Union of Scientific Societies, 1901, 4 pp.
The Adaptation of Seedlings to their Surroundings
By Ethel Sargant.

For some years I have been raising seedlings of plants belonging to the lily family. This very large order includes annual herbs, trees, shrubs, and even climbers, as well as herbaceous perennials and bulbous plants. The characteristic habit of liliaceous plants is, however, herbaceous. The thickened underground stem or bulb is perennial, and, early in each season, produces leaves and flowers which die down at the end. The roots of some forms are perennial; more commonly they appear afresh each season. Such plants are found in the temperate and semi-tropical zones of both hemispheres, and are characteristic of regions with an annual dry season—as the South African veldt—or of Alpine stations where the snow lies for many months in every year, and the flowering season is short and brilliant.

During the annual periods of drought or frost, nothing is seen of such plants above ground. Their underground stems are safely buried many inches below the surface of the soil, but, with the first rains or the flood of melting snow, tufts of leaves and flowers appear with startling rapidity. During the season of vegetation—which, in such climates, is commonly short—the plant is extraordinarily active. The flowers often appear before the leaves, in order that the seed may be formed, may set and ripen within the prescribed time; and the leaves, in their short existence above ground, are forced to replace the food advanced by the bulb for this early start, to supply nourishment directly to the ripening seed, and in many cases to the underground shoots or off-sets which reproduce the plant vegetatively.

An early winter on an Alpine summit destroys all seed not yet fully ripened, and may therefore completely exterminate an annual species. Hence the rarity of annuals at high elevations. Perennials can survive the loss of a single crop of seeds, or indeed of several successive crops. Similarly, a bulbous plant will live through several years of prolonged drought, and finally ripen seeds in the first genial season. The bulbous habit is, in fact, an adaptation to climates in which a period of vegetative activity is regularly succeeded by one of vegetative rest.

The seed of a bulbous or tuberous plant is commonly ripe at the end of an active period of vegetation. When scattered abroad, it is exposed to the uncongenial period which succeeds the fine season. Sound seed easily survives exposure to extreme cold, and will stand a good deal of dry heat, but the young seedling is easily killed by frost, or shrivelled up by the sun. Thus, the most critical period in its life is when the end of its first season of growth approaches. The frost or drought, which could not injure the seed, is fatal to a tender seedling.

Such considerations as these explain the fact that the seed of a bulbous plant, when sown under favourable conditions of warmth and moisture immediately on being gathered, does not often germinate at once. This year's seed, sown in July or August, commonly germinates early in the spring of the following year. In its wild state, a long dormant period is forced on the seed, and the habit persists under artificial conditions.

Another peculiarity of such seedlings is the very early appearance of the bulb. A good example of this is given by Fritillaria plants. Very soon after the seed has germinated, a little swelling in the slender axis shows the position of the embryonic bulb. Before the end of the season the bulb is a structure complete in itself, though no larger than a grain of maize. It is slung on the slender axis formed by the single cotyledon and the primary root, by the membranous sheath derived from the expanded base of the cotyledon. When this axis disappears, the bulb will be left in the ground to lie dormant through the dead season, and resume its growth in the spring. But, in order to resist drought or frost, it is essential that the bulb should be at a certain depth below the surface of the ground. It has been formed on or near the surface by the seed, and before the end of the season it is dragged down by the contraction of the roots attached to it. These roots are themselves fixed in the ground by the roothairs found near their extremities. Thus, the contraction of the roots in their upper part is met by the anchoring of their tips, and the result is that the bulb is pulled down to a depth sufficient to give some protection during the winter or dry season.

If we were able to observe these seedlings in their natural haunts, no doubt many details in their structure would be explained by the influence of their surroundings, but, though we can trace the effect of their native climate or soil in the general structure of such plants, much must remain obscure until we know more of the actual conditions of growth. Thus, the Aloë seedlings which I have raised, are clearly adapted to a dry climate. The seedling does not appear as a slender thread-like axis, as in Fritillaria, for this would be withered by a few hours of hot sun on dry sand. The first thing which appears from the germinating seed is a small green bladder, filled with watery tissue; from this, a root grows downwards and a little fleshy green leaf upwards, its base buried in the watery green cushion which protects it from withering. Later on, when the seedling has grown, and the leaves are capable of flourishing by themselves, the cushion-like sheath loses its watery contents, and is reduced to a membrane investing the leaf base.

Some years ago, I had the opportunity of examining the seedlings of a wild plant growing under natural conditions. This was the wild arum (Arum maculatum), a very common plant in hedgerows and waste places. It appears from the researches of Rimbach that, in Germany, the seeds of this plant are not ripe until September, and that they lie dormant in the ground until the following spring. They then germinate, but the seedling remains underground during the whole of the succeeding year, and the first green leaf is pushed up early in the second season's growth. The observations made by Mrs. Scott and myself in England, shew that—at any rate in the south—the Arum seeds are ripe in July, and begin to germinate in the autumn. They remain underground until the second spring, and thus their subterranean life extends over a season and a half. The cotyledon is, in this case, a hollow cylinder, at the base of which is formed the young tuber. This grows at the expense of the food stored in the seed. When all the food has been completely transferred to the tuber, the whole of the cotyledon is cast off like a cap, leaving the stem-bud exposed. At the same time—i.e., between May and October of the second season—the seedling becomes buried more deeply in the earth. Some seedlings growing in a pan were less than an inch from the surface in May. In October, they were found—after a prolonged search—at the bottom of the pan, or about three inches below the surface of the soil. They are dragged to this position by the contraction of the first adventitious roots, and perhaps of the primary root, too, though this dies away early.

Seedlings of Arum maculatum are very common in the wild state, though the plant is also reproduced vegetatively. We know too little of the reproduction of our wild plants. Many problems of distribution would be cleared up if we knew as much of the adaptation of seedlings to their environment as we know of the adaptation of mature forms, and I suspect that more perennials are commonly reproduced by seed than we are apt to think. It is too often assumed that if a plant is reproduced freely by a vegetative method, its increase is due solely to that method.

A systematic investigation into the reproduction of our native plants in a wild state would, I believe, give very valuable results. We ought to know what proportion of the mature plants belonging to any one perennial species has grown from seed; what the adaptations of the seedling are to the conditions of its life; as well as the methods by which the seed is actually dispersed. Such work is peculiarly suitable to members of a Natural History Society, and if the results were checked and recorded by a specialist in each Club, the body of evidence accumulated by the joint exertions of a number of affiliated Clubs should be very considerable. Such a scheme is, I think, worthy the consideration of the South-Eastern Union.