Again, the mountain climate, with its heavy rainfall and long cold period, tends to the formation of peat; and the acids thus engendered in the soil, as well as the low temperature prevailing during most of the year, render difficult the absorption of water by the roots of plants. The conditions under which alpine plants, then, live may be summed up as follows: a long cold winter, a short summer; great exposure; scarcity of food-supply. The modifications which plants have undergone to meet these conditions are very marked, and render alpine plants a source of constant interest to the traveller and of delight to the gardener. The effect of low temperature (also of peaty soil) in rendering difficult the absorption of food materials, and causing extensive root production and limited stem and leaf growth, is immediately observable. In Fig. 33 is seen an alpine Stonecrop (_Sedum primaloides_) as growing on the Chinese Alps at some 12,000 feet. The root is out of all proportion to the aerial parts. The same plant in the garden forms a little bush with branching stems half a foot long, and flowers borne on leafy axillary shoots a couple of inches long, while the roots are short and tufted. The most characteristic form which alpine plants assume may be called the cushion type. This is produced by excessive branching of the stems of small-leaved plants, accompanied by but little longitudinal growth; and it is excellently shown in many well-known plants such as the Mossy Saxifrages, the Kabschia Saxifrages, the Cushion Pink (_Silene acaulis_), and a number of others. The same type of [Illustration: FIG. 33.--SEDUM PRIMULOIDES. 1/1.]