[Illustration:  FIG. 62.  To show that starch disappears from the leaf when the plant is placed in the dark.  The plant from which was taken the leaf represented in Fig 61, was immediately placed in a dark closet for 24 hours.  Then leaf 4 was taken from it; 5 represents this leaf after the chlorophyl was taken from it:  it is white; 6 is the same after treatment with iodine.  The leaf remains white, showing no starch. (Drawings by M.E.  Feltham.)]

[Illustration:  FIG. 63.  To show that sunlight is necessary for starch-making by leaves.  Leaf 7 had a paper label stuck to its upper surface a couple of hours while the plant was exposed to sunlight; 8 is the same leaf after the chlorophyl was taken out, and 9 represents it after treatment with iodine.  The leaf turned purple in all parts except the part that was shaded by the label.  Starch was removed from the portion under the label, but was not renewed because the label kept out the necessary sunlight. (Drawings by M.E.  Feltham.)]

[Illustration:  FIG. 64.  To show that chlorophyl is necessary for starch formation in the leaf. 10 is a variegated leaf from a silver-leaved geranium; the center is an irregular patch of green, with an irregular border of white. 11, after taking out the green. 12, after iodine treatment, the leaf turns purple only where it was originally green, showing that no starch forms in the white border. (Drawings by M.E.  Feltham.)]

Some leaves on the branch are larger than others because in the struggle for light and air they have had a better chance than the others or they have had more of the food which has come up from the root.

Some of the leaves have developed longer stems than others in their effort to reach out after light and air.

Most leaves have the little mouths through which air is taken in and water and oxygen given out on the rough side, and that side is turned down toward the earth probably so that rain and dust will not choke the little pores.

The leaves of the lower branches tend to spread out in a broad, flat plane because in the effort to get light no leaf will grow directly under and in the shadow of another, while on those branches which grow straight up from the top of the tree the leaves can get light from all sides and so arrange themselves around the stem.

Is it of any value to the plant grower to know these facts about leaves?  It is, for knowing these things he can better understand the necessity of caring for the leaves of his growing plants to see that their work is not interfered with.

HOW THE WORK OF SOME LEAVES IS INTERFERED WITH