I noticed while watering my cacti a few days ago that one effect of all those spines is to trap and hold water droplets. I can understand the advantage this would give plants in temperate conditions -- that eventually the drops will fall off onto the ground, adding a little more moisture to the roots. But I can't help but think that in a cactus' natural habitat, this would be at best pointless. In hot and dry conditions, small water drops would evaporate within minutes. While clinging to the cactus, they could potentially concentrate the sun like a magnifying glass, so that the cactus would be burnt. Can anyone enlighten me?