Most of the water in a cactus is well away from the skin. Take, say, a spider plant fitting in a 6" pot. No part of the plant is more than a couple of millimetres away from the surface, and no part of the leaves is more than a fraction of a millimetre away from the air. In contrast, a cactus the size and shape of a marble has most of its mass a couple of millimetres or more away from the skin, and is further protected from water loss by thick skin.SaiBon wrote:No water at all until spring?! That's amazing! Baffling even!
Leafy plants have a huge surface area and a metabolism to match. Their branches and such are comparable to the spaces inside a lung, and you've probably read that the average lung has the same surface area as a tennis court. A cactus is more akin to the outer surface of the lung, and you'd be lucky if it had as much surface area as the rackets.