This great power of absorbing water and other liquids, so terrible when it leads to overflows, enables peat to be put to various uses, and a good deal of it is sold as peat-moss, for use in stables. [Illustration: Fig. 19. Cutting and carrying peat for fuel, Hoy, Orkney] In the ditches of a peat bog red slimy masses can often be found. They look just like rusty iron, and in fact they do contain a good deal of iron, but there are also a number of tiny little living things present. The {40} stones and grit just under the peat are usually white, all the red material from them having been washed out by the water which has soaked through the peat. Then at the ditch these tiny living things take up the red material because it is useful to them. Peat or "moorland" water can also dissolve lead from lead pipes and may therefore be dangerous for drinking purposes unless it is specially purified. When you study chemistry you will be able to show that both peat itself and moorland waters are "acid" while good mould is not. That is why peat is not good for cultivated plants (see also p. 96). Other things besides peat are formed when plants decay under water. If you stir up the bottom of a stagnant pond with a stick bubbles of gas rise to the surface and will burn if a lighted match is put to them. This gas is called marsh gas. Very unpleasant and unwholesome gases are also formed. [1] The top two inches of soil only were collected here, and there were many leaves, twigs, etc. mixed in. Soils from different woods vary considerably. If the sample is taken to a greater depth the loss on burning is much less, and may be only 5 or 6 per cent. {41} CHAPTER VI THE PLANT FOOD IN THE SOIL Apparatus required. _The pot experiments (p. xiii)._ It is a rare sight in England to see land in a natural uncultivated state devoid of vegetation. The hills are covered with grasses and bushes, the moors with ling and heather, commons with grass, bracken and gorse, a garden tends to become smothered in weeds, and even a gravel path will not long remain free from grass. It is clear that soil is well suited for the growth of plants. We will make a few experiments to see what we can find out about this property of soil. We have seen that a good deal of the soil is sand or grit, and we shall want to know whether this, like soil, can support plant life. We have also found that the subsoil is unlike the top soil in several ways, and so we shall want to see how it behaves towards plants. Fill a pot with soil taken from the top nine inches of an arable field or untrenched part of the garden; another with subsoil taken from the lower depth, 9 to 18 inches, and a third with clean builder's sand or washed sea-sand. Sow with rye or mustard, and thin out when the seeds are up. Keep the pots together and equally well supplied with water; the plants then have as good a chance of growth in one pot as in any other. {42}