A faster colour change of a dry cobalt chloride paper affixed to the lower surface of a leaf than the upper one, indicates that

The faster color change of a dry cobalt chloride paper affixed to the lower surface of a leaf than the upper one indicates that the lower surface of the leaf has more stomata. Cobalt chloride paper is used to detect the presence of water vapor. When exposed to water vapor, the paper changes color from blue to pink. The stomata are tiny openings on the surface of leaves through which water vapor is released. Since the lower surface of the leaf has more stomata than the upper surface, more water vapor is released from the lower surface. This results in faster color change of the cobalt chloride paper attached to the lower surface than the one attached to the upper surface. Therefore, the faster color change of the cobalt chloride paper affixed to the lower surface of the leaf than the upper one indicates that the lower surface of the leaf has more stomata.