How the stem of a cactus plant help the plant to survive?

Answer 1

The stems of cacti are specially adapted to store vast amounts of water for the plant, as well as its food.

The stems are also covered with spines or thorns: this dissuades animals from eating the plant.

The stems also have a waxy coating which reflects the sunlight to further reduce water loss.

Answer 2

The leafless, spiny stem is the characteristic feature of the majority of cacti (and all of those belonging to the largest subfamily, the Cactoideae). The stem is typically succulent, meaning it is adapted to store water. The surface of the stem may be smooth (as in some species of Opuntia) or covered with protuberances of various kinds, which are usually called tubercles. These vary from small "bumps" to prominent, nipple-like shapes in the genus Mammillaria and outgrowths almost like leaves in Ariocarpus species. The stem may also be ribbed or fluted in shape. The prominence of these ribs depends on how much water the stem is storing: when full (up to 90% of the mass of a cactus may be water), the ribs may be almost invisible on the swollen stem, whereas when the cactus is short of water and the stems shrink, the ribs may be very visible.

The stems of most cacti are some shade of green, often bluish or brownish green. Such stems contain chlorophyll and are able to carry out photosynthesis; they also have stomata (small structures that can open and close to allow passage of gases). Cactus stems are often visibly waxy.

Answer 3

The skin of a cactus stem generally has a smooth papery feel. It is firm to the touch if healthy.