Now examine the stem of a seedling sunflower, by cutting a very thin slice across it; you will see in it a ring of strands where the cells are smaller than those of the soft tissue and also much more closely packed (~see~ fig. 93). Then cut a thin slice longways down the stem, and you will see that these more solid strands are the cut ends of long strings of such tissue which run through the stem. The cells which build up these strings are not quite ordinary cells, but are exceptionally long, like water-pipes, and they have thickened walls. These cells do the carrying of water and liquid food up and down the plant (~see~ fig. 94). [Illustration: Fig. 93. Piece of the stem of a seedling Sunflower cut across, showing strands of “water-pipe” cells.] [Illustration: 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. [Illustration: 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). Leaves, as you know, require much water, which comes to them up the stem through the “water-pipes.” You saw already the course of the water-pipes in leaves, for they are the “veins” which we found sometimes make a complete network, and sometimes run parallel in the tissue of the leaf. If you put a leaf stalk in red ink, you will see that the veins are connected with the water-pipe strands in the stalk, for they will both get coloured by the ink as it passes along them.