Herb Paris 2/3 to 1-3/4 inches deep. Solomon's Seal 1-1/3 to 2-1/3 " " Cuckoo Pint (_Arum maculatum_) 2 to 4 " " Colchicum (Autumn Crocus) 3-1/3 to 5-1/3 " " Asparagus 6-3/8 to 13-1/8 " " The water evaporating on the surface of the soil must, as it rises from the permanent water-level below, pass the gauntlet of all these thirsty rootlets and their hairs. Tree-roots will be ready to intercept it at ten feet depth, many herbaceous plants will suck it in at depths of five to six feet, and in the upper layers of soil it will have to pass root-system after root-system from Asparagus to Paris, so that very little will be lost. Perhaps of more importance are the bacteria-germs, and dissolved mineral salts in the rainwater as it trickles down from the surface. The soil particle acts as a filter: at every inch of the descent some of the bacteria and salts will be left, so that by the time the level of Asparagus has been reached there will be exceedingly few, and the water is comparatively speaking pure. The effect of this vigorous underground life is often visible on the surface. Roots, and particularly tree-roots, are often extraordinarily strong. Kerner, in his invaluable _Natural History of Plants_, has a beautiful picture of a young larch tree which had grown in a fissure of a huge boulder. In attempting to grow, the root had forced up part of this stone. It was estimated that it had lifted a weight of 3000 lb., though it was only some ten inches in diameter. Along a dry-stone wall, or even near houses, the growth of tree-roots very often damages the entire wall, which may be entirely overthrown if the tree is too near. The force of the growth of the roots is so great that even a six-foot stone wall cannot keep them down. Quite a young seedling root, in forcing itself through the soil, may exercise a pressure of two-thirds to four-fifths of a pound! This is of course necessary, if one remembers that it has to drive itself through the earth, pushing aside and compressing the earth particles along its course. CHAPTER VII HIGH MOUNTAINS, ARCTIC SNOWS The life of a cherry tree--Cherries in March--Flowering of gorse--Chickweed's descendants--Forest fires in Africa--Spring passing from Italy to the frozen North--Life in the Arctic--Dwarfs--Snow-melting soldanellas--Highland Arctic-Alpine plants--Their history--Arctic Britain--Edelweiss--An Alpine garden. It is impossible to understand and very difficult to explain the sort of life and consciousness which is enjoyed by plants. That they do live is obvious; we know instinctively that they enjoy fine weather in summer and gentle showers in spring, but we cannot prove it. Much of a plant's life is concealed and hidden from us. Even the few explanations which have been given by certain observers are by no means generally accepted.