Recently I posted in the structure of the cuticle which has 2 main components, a hydrophobic layer of interlinking cutin polymer molecules and waxes that are crystalline and protrude from it. As always organisms have evolved to maximise advantages. In this case
the protruding wax shards offer several significant advantages over a smoother liquid wax coating.
Firstly it gives superior water repellency by the Lotus Effect (named after the lotus plant). This is because of 2 synergistic properties, rough surfaces and waxes. The roughness of these crystals or shards trap pockets of air beneath water droplets.
Due to the high contact angle and the surface tension of water, the latter forms droplets as it cannot flatten out and wet the surface. The droplets roll off the hydrophobic surface easily washing away dirt and bacteria etc.
The wax shards offer solar and thermal protection by light and UV scattering. They also have a role in gas exchange regulation. The crystalline structures form a porous, breathable network allowing necessary oxygen and carbon dioxide exchange while slowing down water vapour loss though the cutin down to the lenticels below.
Interestingly the cuticle changes into a smoother continuous liquid wax layer near harvest ripeness which seals the lenticels pores as the metabolism in the apple changes to starch breakdown.
