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 [Illustration: FIG. 10.--COMMON PRICKLY PEAR CACTUS (_Opuntia Opuntia_) Native along the Atlantic Coast. The green joints of the stem function as leaves and store water.] 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 [Illustration: FIG. 11.--BUTCHER’S-BROOM (_Ruscus aculeatus_) Note leaflike stems with flowers arising from the center.] absence of leaf surface is a decided advantage. In many partly desert or dry regions this production of leaflike stems or branches is common, an excellent garden example being asparagus, which came originally from Europe and the feathery growth of which is all stem. In Tasmania a kind of yew tree produces no leaves, all the foliage being modified stem, which is true of many kinds of spurge in the West Indies, where an almost impenetrable scrub is largely made up of a shrub which is apparently covered with leaves, all actually part of the branches and stems. [Illustration: FIG. 12.--DUCKWEED The smallest known flowering plant, with _no_ leaves and tiny leaflike stems floating on the surface. Flowers are borne from the margin of the stem. (Eight times natural size).]