Page:An introduction to physiological and systematical botany (1st edition).djvu/54

 24 and a new cuticle, covering a new layer of the same succulent matter, is formed under the old one. Annual stems or branches have not the same power, any more than leaves. But little attention has been paid to this organ till lately, though it is very universal, even, as Mirbel observes, in Mosses and Ferns. The same writer remarks that "leaves " consist almost entirely of a plate of this " substance, covered on each side by the " cuticle. The stems and branches of both " annual and perennial plants are invested " with it; but in woody parts it is dried up " and reproduced continually, such parts " only having that reproductive power. The " old layers remain, are pushed outward " by the new ones, and form at length the " rugged dry dead covering of the old trunks " of trees." When we come to consider the curious functions of leaves, we shall find this part to be of the very first importance. In it the principal changes operated upon the juices of plants by light and air, and the consequent elaboration of all their peculiar secretions, take place.