The stems of some plants, such as the Big Trees of California, for instance, are among the oldest and most permanent of living things. “General Sherman,” one of the biggest in that most famous grove, was nearly three thousand five hundred years old when Columbus discovered America; it has lived through all the great periods of modern history, and to-day it is over 270 feet high and 35 feet in diameter. No living thing is so large or has lived so long. In Australia are great forests of blue gum trees even taller than our Californian Big Trees, but not so old nor so thick.
In the Pacific, off the coast of Oregon and British Columbia, a seaweed is commonly found with stalks over 500 feet long, and in India the rattan palm climbs over the tree tops for great distances, a single stem not much thicker than a broomstick measuring over 700 feet long. The search by leaves for light and air results in the stems of some plants performing almost incredible feats. Whether it is one of the Big Trees with a great massive trunk, or the rattan palm with its sinuous winding through the topmost heights of the tropical forests of India, the result is always upward to a “place in the sun.” This struggle for sunlight has taken many forms in different plants, the ordinary vines like morning-glory or grapevine, for instance, where the climbing stem is of great advantage. Some vines always twine to the left, as the hopvine, others to the right, as in the morning-glory, all seeking support from something else, each adopting its own most useful way of getting its leaves in the most advantageous position to catch the life-giving sunshine. If we could look down on any forest from an aeroplane, the striking efforts of nearly all plants, whether herbs, shrubs, vines, or trees, to get the utmost sunshine for their leaves would be evident at once. No apparently impossible twisting or bending of tree trunks or reaching out of stems of vines but is to be found in the inexorable struggle of stems to fulfill their task of giving the plant its chance to reach “a place in the sun.” Sometimes mere climbing or twining does not seem sure enough—it seems as though winds or the elements might break loose the vine from its support and thereby kill its chances. In certain vines this contingency appears to have been foreseen, and as if to clinch their opportunity of growing onward they are provided with special helps. Slender green tendrils, delicate prolongations of the stem, begin, almost insidiously, to catch hold of the nearest support and by a couple of turns about it and subsequent strengthening of their tissues make a permanent holdfast. The grapevine is a case in point. And as if this were not enough, certain other plants, such as the Boston ivy, have small disks which attach themselves to bare walls or tree trunks. This is to make assurance doubly sure, and it is this that makes the Boston ivy so useful to the gardeners for covering walls.
Some stems accomplish their purpose not by holding fast to a support in the air, but by creeping along the ground, as in the running blackberry, and often in the Virginia creeper. The purpose is the same, and, as if to confirm it, a few otherwise quite prostrate vines have their tips turned upward to the light, notably in the case of the creeping speedwell.
In certain plants the stem may assume curious forms due to special conditions under which they live and to which adjustment is necessary for the plant’s existence. In deserts, for instance, the cactus produces practically no leaves ([Figure 10]) and the green stem performs not only the function of leaves but acts as a storage for water. Where water is scarce this is of tremendous advantage, a single cactus having been known to store up 125 gallons. A similar habit of the cactuslike spurges in South Africa gives as weird an atmosphere to parts of their landscapes as we find in Arizona. It is as if the stem of such plants, being unable to push its leaves (it has none) up into the light, takes over some of the functions of leaves and makes up the deficiency by adopting other methods
to secure the plant’s survival. Other stems, looking and acting like leaves, reveal their true nature by producing buds, and the curious feature of the common butcher’s-broom ([Figure 11]), often colored scarlet for Christmas decorations, bearing flowers from the middle of what is apparently a leaf, but is actually a modified stem, is explained by this ability of stems to modify their habits to suit conditions. The butcher’s-broom is an inhabitant of dry regions along the Mediterranean, where a reduction or