Fig. 93. Piece of the stem of a seedling Sunflower cut across, showing strands of “water-pipe” cells.
Fig. 94. Piece of stem cut across and then split lengthways, showing the strands of thicker “water-pipe” walls.
You can see that the water travels up these cells if you cut across a stem near the root and place it in a little red ink. After a few hours if you cut a section several inches from the bottom of the stem you will find that these strands are coloured red by the ink which has passed through them, while the rest of the stem is very little coloured, or quite colourless. This shows us that these strands are the special water-pipes of the plant.
Fig. 95. Cross section through a Lime twig three years old seen with a magnifying glass.
Large numbers of such cells closely packed together, and with some other hard cells between them, make up the wood in woody stems. Cut across a small twig of lime or oak and examine it with your lens. Outside is the brown bark, then within that some green cells and a little soft tissue, while most of the stem is made up of a mass of hard wood cells, among which you can see some of the larger water vessels distinct from the rest. All this hard tissue really corresponds to the joined up separate strands which we saw in the sunflower stem (see fig. 95). Trees like the lime and oak, which live for a long time, grow for a certain amount every year, and each year they add a ring of wood to their stems. In old stems you can see clearly the rings of wood which have been formed by each year’s growth. This is another way of telling the age of the stem, and you should compare your results from this method with those you got from counting up the bud scars (see p. [75]).