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Show 322 THEIR VALUE. all the mould of the heights into the valleys, and the portion of land fit for bearing vegetables of any kind would decrease every year. Nor would there be merely a decrease of the productive surface, there would be a deterioration of the portion left. The soil which immediately produces the mosses, and lichens, and other plants of the high and cold grounds, is not adapted for the production of the soft grasses and :flowers of the valleys: and these valleys are not suited in climate for the upland plants, thouO"h those plants and the soil in which they grow both o tend to cool the climate and bring it nearer to their native one. Thus, if these plants were to "give way" in the autumn, as is the case with many of the plants lower down, the meadows would annually be strewed with unwholesome earth, which would in time destroy their fertility, and they would become bogs and quagmires. But the matting of mosses and lichens keeps the soil together, and equally prevents it from being washed away by the rains, and blown away by the winds ; so that when the cold weather comes the soil is not much lessened in its quantity, while it is softened and divided by the frost, and thereby fitted for the action of the roots of those plants, the stems of which die down annually. In plants of that kind, more especially in those that have fleshy or bulbous roots, which most of the plants that die down in the winter in cold places have, the crown of the root is usually the vital part, so that if that s~stains much injury t~e plant is killed. Now the wmter ~rop of ~asses IS of great service to plants of that kmd. It IS not the absolute temperature that kills plants, it is the greatness and especially the rapidity of the changes; and if the operation could be performed gradu~lly enough, it is possible that any plant (even those whiCh are kept in the artificial heat of stoves in this country) could not only bear the frost, but actually to be f~ozen without much injurv. The progress of ordmary SPRING ]..,LOWERS. 323 freezings and thawings is, however, rather rapid for the safety even of native plants, unless the roots are deep in the soil-deeper than soil is usually found to be in cold upland places. Gardeners find great pro~ tection to fleshy roots in the ground, from covering them over with straw and litter before the frost; and the moss and lichen act, in those places where they come, as if they were a coat of natural litter. Owing to those protections, the spring :flowers, though not very abundant, come much sooner in those mossy places than one would expect, though they neither come so soon nor are so fine in their qualities as those in places which are covered with snow early in the winter, and remain in that state till the spring. If the snow lies long on a spot where the roots are, the snow-drops will absolutely push their little starry cups through it. But these humble crops are as serviceable in the warm season as they are in the cold. Many of them absorb moisture at their whole surface, and all of them retain it in their thickly matted forms, so that they keep places in a moist and fertile state which, but for them, would be entirely parched. When the heath has been burnt on a mountain surface, or that surface in any other way laid bare, it is truly astonishing how speedily it becomes clothed with green mosses. These keep the surface cool, whereas the rays of the sun, beating upon it, would heat it like an oven, and it would be converted into blowing dust and when summer rains did fall, they would b~ instantly removed by :flowing off and being evaporated; and although the moss 'presents much more surface to the air than that of the soil on which it grows, it is so much cooler that the evaporation from it is considerably less. The absence of mosses i~ among the reasons why sandy and chalky places are so soon parched up. But although, within certain limits, the growth o .. those plants is good, yet, whe:l those limits are ex- |
