(drought-resisting plants)--in roots, or stems, or leaves, which become much enlarged, and at the same time covered with a [Illustration: FIG. 4.--WILD CARROT (DAUCUS CAROTA), GROWING UNDER GREAT EXPOSURE. 1/2.] highly impervious skin, so that they act as veritable cisterns. In plants like the Cacti water storage in the stems is carried very far indeed; while in such genera as the Stonecrops (_Sedum_) the leaves are often so swollen and charged with water that they lose up to 98 per cent. of their weight if they are dried. Prevention of excessive loss of water by transpiration is effected in plants of dry places mainly by reduction in the size of the leaf and by protection of its surface. Leaf reduction is very marked in many dry countries. If we compare the flora of the Mediterranean region (a dry area) with that of Middle Europe or of England, we shall be struck with the prevalence in the former of small-leaved twiggy plants--Lavender (_Lavandula_) and Rosemary (_Rosmarinus officinalis_) will serve as examples. Often leaf-reduction is carried much farther, and we need not go beyond our own commons to find a good example, for in the Gorse (_Ulex_) flat leaves are entirely absent and the branches are shortened and converted into prickles, thus largely reducing the surface exposed to the sun and wind. The seedling Gorse has little trifoliate leaves, which remind us of its affinity to the Trefoils and Brooms, but they are discarded almost at once, to fit the plant better for life in the dry, breezy localities which it favours. Reverting to the Mediterranean flora, a characteristic of its plants is the prevalence of a grey hue in their stems and leaves, such as we see in the Pinks and Achilleas of our rock gardens. This is due to a coat of wax, as in the Pinks (_Dianthus_), or a felt of hairs, as in the Achilleas, designed to check excessive transpiration. The coatings of hairs are often of great beauty and complexity, and form an almost impenetrable covering to the leaf surface, protecting the upper side from the fierce rays of the sun, and on the underside sheltering the stomata, or minute openings through which the plant exhales the surplus water drawn up from the roots and inhales carbon dioxide. Another very beautiful device for protecting the underside of the leaf, and one which may be studied in many of our commonest plants, consists of the inrolling of the edges, often combined with a wrinkling or ridging of the underside, so that the stomata are set in deep hollows, communicating with [Illustration: FIG. 5.--SECTION ACROSS INROLLED LEAF OF CROWBERRY (EMPETRUM NIGRUM), MUCH ENLARGED.]