The word cactus makes us think immediately of spines. Although a few kinds of cactus are spineless, the stems of the most are covered with an array of sharp spines. A cactus makes food in the thin, green outer layer of its stem rather than its leaves. In adapting to dry habitats, most species of cacti have modified their leaves into spines otherwise too much water would be lost through the pores. The spines are actually modified leaves growing from spots or bumps called areoles. The areoles occur in rows or spirals along the stem. Each one is made of two buds tightly presses together. Thus the spines always occur in clusters that differentiate them from similar-looking plants.
The spines come in variety of shapes. They may either be short and stout, long and straight, needle shaped, feathery or hair like spines.
Naturallythe spines protect their stems from becoming fleshy food for the animals. But this is not their only function. One important function is to screen the sun’s rays thereby keeping the plant cool. They also help trap a layer of air close to the plant and help reduce evaporation. They also collect raindrops and dew, gently dropping water under the plant, where it soaks into the soil and is eventually absorbed.