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in developing large black seeds, which are embedded in a pulp that not even an anthropoid ape could eat with any pleasure.

"Is it possible that the slightly bitter, dry, tasteless, white pith surrounding these large inedible seeds could have been any attraction to primitive man in Africa, so that he protected and fostered one of these species of Musa until it developed into the cultivated banana, exactly like the cultivated banana separately developed in Eastern Asia?

"It would be difficult in any case to make a Nuganda of to-day believe that his beloved food substance which provides him with a mass of nourishing vegetable pulp, with a dessert fruit, with sweet beer and heady spirit, with soap, plates, dishes, napkins, and materials for foot - bridges, was not always indigenous to the land he dwells in, and of which it has become the distinguishing feature.”

CHAPTER XIV.

NATURAL SELECTION OF SPECIES.

THE Outcome of the struggle for existence is, as we have seen, the elimination of the less fit; but the selection of races is determined more by conditions of existence than by direct conflict between competing species-more by quality of soil and climate than by a direct struggle between individuals of different

races.

We believe that by natural law every locality tends to produce the most highly organised race of animal or plant that its soil, climate, and other conditions can adequately support. In other words, Nature automatically selects the race that makes the greatest demands on resources she can supply, and thus determines the predominance of a particular species of animal or plant in a locality.

In civilised countries the distribution of the larger mammalia is due to man's inter

vention, and therefore examples of Nature's method of selecting races are few; but we know that the size and quality of domestic animals depend on the quality of their food and conditions of life. Graziers, for example, can tell by the appearance of cattle or sheep the character of the pasture on which they have been reared. The superior quality of Lochleven trout, so well known to the angler and the epicure, is due to the character of the bed of the lake. Its fertile mud is covered with highly nutritious aquatic plants, on which molluscs and other forms of life find abundance of food; these, again, provide generous nutrition for fishes, and they respond both in number and quality. Trout in streams or lakes on mountains composed principally of granitic rocks also exemplify the law, but in the opposite direction. Neither the soil nor the water in such localities contains much nutrition for plants or the lower forms of life; food is in consequence scanty and innutritious, and the trout small in size and poor in quality.

It is, however, in the vegetable world that Nature's law of selection can be most easily studied. Among the Rothamstead agricultural experiments one of the most interest

L

ing and instructive is a series of plots showing the effects of different manures on pastures of mixed grasses.

The plots were differently manured for many years, the same manure being continuously applied to each, but they were neither cultivated nor artificially seeded, yet in the course of years the proportions of the various grasses in the several plots have greatly changed. Where manure, chiefly of a stimulating character, had been applied, the coarse, rank, innutritious grasses have largely increased; and where another kind enriched the soil principally with mineral food, the fine, highly nutritive grasses have prevailed and ousted the coarser and ranker varieties, although the latter are in appearance more robust.

Success in farming is largely based on this principle of natural selection, and its operation is very noticeable in bringing an exhausted farm, overrun by weeds, into a high condition of fertility.

So long as the farm remains poor in condition the weeds cannot be eradicated, because the land does not contain subsistence for anything better. But when the resources of the soil are sufficiently reinforced to produce a good crop of cereals,

the weeds, without being directly attacked, disappear, not because there are no seeds in the soil-seeds there are in abundance -but because its fertility can now meet the demands of more highly organised plants, and the conditions are in sequence unfavourable to lower forms of vegetation.

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The gardener knows that every plant prefers a certain quality and texture of soil, and that it is as impracticable to grow some in rich soil as others in poor.

In virgin countries beautiful grassy glades may sometimes be seen in a primeval forest, or groups of trees adorning grassy slopes, as in an English park.

In one locality the soil could provide the sustenance necessary for the more highly organised grass, and it prevailed against forest trees: where the resources were inadequate for grass Nature selected

trees.

When an old forest dies, the trees that naturally replace it are usually of a different species from their predecessors, and sometimes new in the locality. The climatic conditions may have remained unchanged, but the timber of the old forest had appropriated so much of some of the mineral

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