4. Water culture.—Fix two similar young plants in corks as shown in Fig. 19, and put the corks into two bottles, the first of which contains pure water and the second the nutritive solution, and let the roots of the seedlings dip into the liquids. Cover the outsides of the bottles with rolls of paper to keep out the light. Notice that [Pg 28] the plant living in the nutritive solution thrives, while the other presently withers. Dry and burn the former, and observe that it yields more ash than does a seed such as that from which it sprang. 5. Plants obtain their mineral food from the soil by their roots.—As the roots are the only parts of the plant which are in contact with the nutritive solution, or which (under ordinary conditions) are in the soil, the mineral matter must be taken in by the roots. 6. The root-hairs.—Take up a seedling which has been growing in damp sand, and observe the small particles of sand adhering to the root-hairs (p. 17). The hairs of a plant’s root and rootlets apply themselves very closely to particles of soil (Fig. 20), and the mineral food (dissolved in water) passes into the hairs and so gets into the root and thence to the other parts of the plant. 7. Roots as storehouses of food.—Examine, before the plants flower, the roots of a turnip, a carrot, and a radish, and notice how greatly they are swollen. You know that these roots are valued as foods; of what use do you think the stored food is to the plants themselves? The food of a young seedling.—When such a seed as that of a bean is germinated in damp sawdust or wet clean sand, and kept in a warm and light place, it puts out a radicle, which grows downwards and becomes the main root, and a stem which grows upwards and bears green leaves. After a time the main root branches, giving off side roots, which spread in all directions through the sawdust or sand. The main root and the rootlets bear very fine fluffy hairs for a short length, which is situated just behind their points (Fig. 11), and these root hairs come into very close contact with particles of damp sawdust or sand (Fig. 20), the moisture passing into them and thus reaching the main root, from which it is distributed to the various parts of the plant. The stem likewise flourishes, growing in length and thickness, and putting out new leaves. [Pg 29] All this time the young bean plant is living on the food material stored up in its cotyledons (p. 6); and if the sand or sawdust is kept moist, with even pure water, this seed food is at first quite sufficient. When at last the seed food is all used up, however, and all that remains of the cotyledons is a shrivelled skin, the plant begins to droop and wither from lack of food.