"As the roots are feeding and storing places, so the stem is a sort of passage way for the passing back and forth of liquids. Take a stem of a big plant, like an oak tree, and you see in the wood where storage of fibre has gone on. But the great work is that of interchange. "Leaves are very active portions of the plant. They represent a great, busy manufactory. Manufacturing what? That question I see stamped on Myron's face so plainly he need not speak it out. Manufacturing real food out of raw material--that is the work of these plant shops. "Let me tell you about this. Ethel has in her hands two little plants. The one in her right hand has been growing in the light; the other, in her left hand, has been put away in the dark to grow. The absence of green colour is very marked in this latter plant. So you see it takes light to form this green, or chlorophyll as it is called. The chlorophyll-saturated cells, absorbing carbonic acid and the water-diluted food from the soil, literally break them up. And when broken, food is found suitable for plants to absorb. Wonderful, is it not? "I spoke of carbonic acid; well, this is a gas, as some of you have found out before, made up of carbon and oxygen. It is a gas which we of the animal kingdom breathe out as waste from our bodies. The plant takes it in through the leaf--and, by the way, I ought to explain that. It is this way: if we had a magnifying glass we should find over the inner surface of leaves, pores, or stomata as they are called. They open in the presence of light; and from these openings what the plant has no use for passes out, and gases from the air may pass in. Some call these openings breathing pores. "Quantities of water pass out through these pores. When this process goes on too rapidly a plant will wilt. "So, to go back, we will suppose that carbonic acid gas has passed into the leaves. Straightway the chlorophyll bodies get to work. The gas is broken up, and oxygen and carbon are left. The carbon is wood the plant builds. Some of the oxygen passes out into the air and some is kept for plant food use. "It is a good thing for us that some of the oxygen does escape into the air for we need it. So you see we, in our respiration, and the plant, in its breathing, are doing each other a good turn. "Of course, there is the dilute food from the soil, which is largely mineral matter and water. The chlorophyll bodies work away on these minerals, and make them into foods. A great body of water, as I have said before, passes out of the plant through the stomata. "I have told you a thing that the plant can do which we are not capable of doing. A plant takes a mineral and makes it over into food. You and I, unless we happen to be circus glass-eaters, are not built to do this work. But the vegetables which we eat do the work for us.