Keeping the temperature of a cactus constant

 Mrs B has just made a cactus pin cushion.

I've been reading Plant Physiology by Salisbury and Ross. They assert that all biological processes can be explained in terms of chemistry and physics. There is a great chapter on how thermodynamics affects plants. They state: "The high specific heat of liquid water is caused by the arrangement of its molecules, which allows the hydrogen and oxygen atoms to vibrate freely, almost as if they were free ions." This large specific heat capacity has implications for organisms like cacti that contain a lot of water. It means that no matter how hot or cold it gets outside over a 24 hour cycle, the internal temperature won't change much.