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_)? [Illustration: FIG. 35.--MOUNTAIN AVENS (DRYAS OCTOPETALA). 1/1.] As we mount higher and higher on the hills, plants become fewer and more stunted, but hardy forms persist even long after the level of perpetual snow is reached. In the Alps, _Ranunculus glacialis_ occurs up to an elevation of about 14,000 feet. In West Tibet, strange stunted species of _Saussurea_, a genus of _Compositæ_ allied to the Thistles, exist at elevations of 17,000 to 19,000 feet. Some of the Cryptogams go higher still. Lichens grow on the summit of Kilimanjaro (over 19,600 feet); and Schimper suggests[11] that this may by no means represent the absolute limit of vegetation. The prevalence of snow and ice does not of itself inhibit the lower forms of life. Since “red snow” was shown, nearly a century ago, to be due to colonies of a minute Alga, many microscopic organisms of like habitat have been discovered, and these algal colonists of snow and ice are now known to extend far over the frozen deserts of the highest hills, and to penetrate into the remotest regions of the Arctic and Antarctic.