The path of the water in the stem.—It may easily be shown that water travels up the stem to the leaves. It is common knowledge that [Pg 70] slightly withered leaves or flowers become fresh and crisp again if the twig or stalk is put in water. If the stalks of white flowers—say snowdrops or narcissi—are put into water coloured with red ink, the flowers become veined with red, and, if the stalks are cut into, red strands may be seen. This experiment not only shows that water has travelled up the stalk, but it also shows that the water has passed along definite channels. When a vine stem is cut back in the spring, the water wells out rapidly from the end of that part of the stalk which is still in the ground. This bleeding, as it is called, may also be seen, though to a smaller extent, in stems of sunflower, scarlet-runner, and other plants. By drying the cut surface with blotting paper, and then examining it with a lens, it may be seen that the water escapes from the ends of certain little tubes; and it is possible in a boiled or rotting stem (Expt. 11. 4) to follow the distribution of the strands containing these tubes. The strands run along the length of the stem, outside the pith. Cross strands connect the main ones, chiefly at the leaf-levels (nodes); and other strands run out into the leaves to form the veins. The tubes which convey the water current are in that part of the strand which is nearest the pith, and they become woody. Thus, if the current year’s growth of, say, a horse chestnut or an elder twig is cut across, a thin ring of wood is seen surrounding the soft pith. Outside the wood are the softer tissues, surrounded by the bark. A ring of the bark and soft tissues beneath it may be entirely removed from a growing twig, leaving the wood exposed, but the leaves above remain crisp and fresh, showing that this treatment has not interfered with their water supply. The water, therefore, travels along either the wood or the pith. That the wood and not the pith conducts the water may be shown by putting a leafy twig in water coloured with red ink. Only the wood is stained. [Pg 71]