You have now seen that seedlings require ~water~ for their life just as animals do; and also that young plants are provided by their parents with a store of ~food~ which is largely ~starch~, and which they use up during their early growth. CHAPTER IV. FOOD MATERIALS OF THE OLDER PLANT (1) IN THE SOIL As we have just seen, young seedlings are supplied with stores of food, starch, and other things, which are packed in their cotyledons and are used up by them as they grow. But we also saw that as the plant gets older these stores get emptier, and finally the nurse leaves shrivel up entirely when their contents are exhausted. All the same, however, the plant continues to grow. Surely it cannot do this on nothing, any more than an animal could? When the young calves cease to be fed with milk, their food changes, and they begin to eat grass; this gives them individually more work, for grass is not a “prepared food” like milk. Very much the same thing happens with seedlings. ~Their prepared food supply gets used up, and they must find food for themselves. Where do they find it?~ When you remember the fine hairs on the young parts of roots which absorb water from the soil or sawdust, it is quite natural to think at once of the soil as a possible place for them to find their food; and, indeed, this is partly the case. The water in the soil is not perfectly pure, for there are many different “salts” dissolved in it. By “salts” one does not mean only table salt, but also any kind of mineral in solution, such as salts of iron or portions of chalk or limestone, or even some of the minerals which make up granite. These may all be dissolved in rain-water just as sugar is dissolved in your tea, and so spread equally through it. As the water enters the roots of plants through the hairs, these dissolved salts come in with it, and so get distributed over the whole plant. The root hairs cannot “eat” particles of soil, but they twine in among the fine grains and absorb the little films of water which cling to them. [Illustration: Fig. 9. Root hairs growing among soil particles. (~Much magnified.~)] You can find out some of =the importance of these mineral salts= in the life of the plant, if you do the following experiment. Take several seedlings which have already grown enough to have nearly exhausted the supply of food in their cotyledons. These you must grow in jars of pure distilled water, to which you have added certain salts which have been found to be the important ones in the soil water and plant food. By giving the plant nothing but these salts and distilled water you know just what it gets. Distilled water is made by catching and condensing steam, and it has no salts dissolved in it; while ordinary tap water has run off some mountain side or risen in some spring from the rocks, and it has many salts in it already, so that it is useless for this experiment.