What is Inside a Cactus?

On the inside, a cactus plant has tissue. Central transport tissue takes water up from the shallow, fibrous roots and into the stem. Storage tissue within the stem holds water, dissolved nutrients, and photosynthetic products such as starches and sugars. The amount of water within the tissue may be guessed from the outside. The outer surface of the cactus has ribs that expand or contract with more or less water reserves.