[Enclosure]

Many leaves are covered with bloom, that is with excessively minute cylinders or points of a waxy substance. This retains a layer of air, so that if the leaf is submerged it looks coated with silver, & some leaves may be kept submerged for a week, & when taken out of water are quite dry. If the bloom is sponged off a gathered leaf, & it is hung in the air it dries much quicker than one with the bloom on it. Yet I cannot believe that the sponging can remove the wax out of the excessively minute pores through which it is secreted. Why then does a sponged leaf dry quicker? Is is possible that the layer of air entangled or in contact with the little waxy points, parts with its vapour of water more slowly than does a layer of air in contact with a sponged leaf? Can the diffusion of the vapour from the leaf be thus checked?⁴

C. Darwin