You will find that you yourself, as well as all animals, not only use up a part of the air, but also give out a waste product which we call carbonic acid gas. You can see one of the characters of this gas from your lungs if you take a jar of lime water and breathe into it for some time. Compare this with a similar jar of lime-water through which ordinary air has been pumped at about the same rate for the same time, and you will see that the one you have breathed into has gone very much more cloudy-white than the other (~see~ fig. 2). The cloudiness in jar A is caused by the waste gas (carbonic acid gas) which you breathe out, and which combines with the lime in the lime-water to make solid grains of chalk. Fine white chalk grains always form in lime-water when this gas is present, so that a jar of clear lime-water is a very good test for the presence of the gas. [Illustration: Fig. 2. Jar A contains lime-water through which human breath has passed. Jar B, lime-water through which ordinary air has been pumped for the same time. Note how much greater is the milky deposit in A than in B.] The giving out of carbonic acid gas is one of the most characteristic things about animal breathing, and we can show that plants in breathing give out this gas too. To prove this, take another jar with a well-fitting cork, and put some beans and peas, which are just beginning to grow, into it, with a little damp blotting-paper to keep them sufficiently moist. Leave the jar closed for a day or two and then open it and quickly and gently pour in some lime-water. Put the lid on again at once and shake it up. You will find that the lime-water turns quite milky, showing that ~the same waste gas is given out by the plants as was given out in your own breath~. These experiments show us that plants breathe in a part of the air, and also breathe out some of the same waste gas which is given off by animals in breathing. So that we have found that ~plants do breathe~. Now to go to the other signs of life. I think you will hardly need to do any special experiment to show that seedlings =grow= into big plants, you must have seen it so often for yourself in the woods and fields and gardens. We have still to show that plants eat and move, but before we can do this properly, we must learn a little more about the parts of the bodies of the plants themselves, for they have quite a different set of organs to those we are accustomed to in animals, and their way of eating is so different from that of animals that we cannot understand it immediately. CHAPTER III. SEEDS AND SEEDLINGS If we wish to follow the whole life of a plant, we cannot do better than begin by watching the baby plant “hatching” out from its seed at the beginning of its active life.