G. 61.
To show that growing leaves contain starch. 1. Represents a green
cotton leaf as picked from the plant. 2. Is the same leaf after taking
out the green coloring matter; the leaf is white. 3. The same leaf
after treatment with weak iodine turned to a dark purple, showing the
presence of starch. (Drawings by M.E. Feltham.)]

[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 ano