While stems, such as the Big Trees or the giant cactus, may be among the largest of nature’s creations they may be also the smallest, as the duckweed that floats on ponds is the tiniest of all flowering plants and its flat expanded surface is wholly stem. Figure 12 on this page better illustrates this strange modification of a stem than words could do. From what has been read it will be seen that stems are not “just stems”--they are among nature’s most ingenious devices to secure the survival of the plant. Whether buried in the ground, and producing, almost by stealth, buds that develop into mature plants, or thrusting leaves to the utmost limits of their reach, or climbing by an intricately varied mechanism, or changing their character to suit desert conditions, or floating on the water--it matters not. Each modification of form or use secures to the individual plant its chances to survive; and in most cases its only chance, as anyone may see by the sudden death which follows a series of changes which prevents a stem from performing its proper tasks. THE LEAF As the palm reader is supposed to be able to tell your history and future from veins in your hand, and as the veins in the wing of a butterfly tell their story to an entomologist, so the veins of a leaf are more significant than almost any other characteristic of a plant. Most leaves have their veins, or skeleton, with a single midrib and many branches off it on each side, which themselves break up into a fine network of veins. Such leaves are _netveined_ (Figures 13-24). Others, such as corn and grass, have the veins running side by side from one end of the leaf to the other, sometimes with small branches off them, but instead of the veins forming a network they are parallel, and such are called _parallel-veined_ leaves (Figure 38). In the chapter on Plant Families and Their Relationship more will be said as to the amazing regularity with which netveined leaves are associated with certain kinds of flowers and parallel-veined with other kinds, how these distinctions have been recognized since hundreds of years before Christ, long before their true import was understood. There are variations from both these [Illustration: BANYAN TREE (_Ficus bengalensis_). A fig tree of India, whose adventitious roots make frequent connection between the tree top and the ground. Starting as thin, whiplike streamers these roots ultimately form new trunks. (_Courtesy Brooklyn Botanic Garden._)] [Illustration: LACELEAF (_Aponogeton fenestralis_). A submerged aquatic plant, with permanently skeletonized leaves, and an inhabitant of forest pools in Madagascar. (_After Engler & Prantl. Courtesy of Brooklyn Botanic Garden._)] [Illustration: ROOT HAIRS WITH FINE SOIL PARTICLES ATTACHED. Note soil, water, and air spaces. Much magnified. (_After U. S. Department of Agriculture. Courtesy of Brooklyn Botanic Garden._)] [Illustration: FIGS. 13-24.--FORMS AND TIPS OF LEAVES