Moll's half-leaf experiment: half a leaf covered with black paper stays yellow (no starch) while the exposed half turns blue-black with iodine — light proved necessary in one leaf. A variegated (green-white) leaf: only green parts give the starch test — chlorophyll proved necessary. KOH in a bell jar absorbs CO₂ — the leaf makes no starch; the control leaf does — CO₂ proved necessary.