plant growth is characteristic of semi-desert regions, where the points of similarity of environment to those of the mountain-tops are evident. This cushion form has many advantages for the alpine plant. It keeps it warm in winter and cool and damp in summer; it allows it to produce a great amount of blossom without the necessity for extensive growth; it resists the utmost efforts of furious gusts of wind almost as well as would a half-buried stone; on the most storm-swept cliffs its fresh green blobs “welcome every changing hour, and weather every sky.” [Fig. 32] shows a boss of this kind, composed of the Cushion Pink (Silene acaulis), with an admixture of Filmy Fern (Hymenophyllum unilaterale) and a Moss (Mnium hornum). The shrubs of the alpine zone are mostly small and creeping, weaving themselves among the vegetation, and with low grasses and sedges forming a mat which is equally resistant to all inimical conditions. Their leaves are small, to avoid damage by wind or by excessive transpiration. In some genera—for instance, Veronica—the diminution of leaf surface accompanying more elevated habitat is very striking. In the New Zealand lowlands broad-leaved forms ([Fig. 34], left) are met with, which give way, as one ascends to 8,000 feet, to such forms as V. Hectori ([Fig. 34], right), in which the leaves are reduced to mere scales, and the plant much resembles some of the Cypresses or other Conifers with marked xerophile characters.
Other plants, again, escape climatic rigours by burrowing underground and throwing up short aerial stems in summer; the spindly plants of the lowland, with diffuse stems, and also the light-rooted annuals,
Fig. 34.—New Zealand Shrubby Veronicas, showing, from left to right, reduction of leaf with increasing elevation of habitat. 2/3.
are conspicuous by their absence. The brief summer and long winter are unsuitable to the economy of annual plants; and the alpine perennials are so constructed that with the passing away of the cold, flowering and fruiting may be accomplished quickly, before winter descends again. The abundance and vividness of the flowers of alpines is almost proverbial. Several explanations have been put forward to account for these features, and probably there is some truth in each of them. It has been held that the brilliancy of the sunlight is accountable; the shortness of the period available for seed-production, and the consequent need of prompt pollination by insects, have been suggested, as leading to urgent advertisement by means of brilliant coloration; while the fact that the pollinating insects are largely Butterflies, the most æsthetic of flower visitors, has also been put forward as accounting for it. Be that as it may, the glowing patches of colour produced by many quite minute alpine plants are among the most delightful things in nature. Our own flora contains but few of the more striking of these jewels; but where will one find a more delightful sight than a well-flowered patch of Spring Gentian (G. verna) or Mountain Avens (Dryas octopetala) or Purple Saxifrage (S. oppositifolia)?
Fig. 35.—Mountain Avens (Dryas octopetala). 1/1.