the cactus had evolved spikes, rather than leaves, in order to reduce the surface area through which it could lose water, while still providing some shade for the main body of the plant, often little more than a modified stem; many people, he said, wrongly assumed that spikes served only to ward off predators. He also remarked on the cactus’s thick waxy skin, its well-developed root system and its broad, succulent trunk, all of which facilitated the storage of moisture or the minimization of its loss.
