Internal Adaptations of Cactus Plants

Storage Tissue

• Under the firm, exterior skin of some cactus species are specialized tissues made of parenchymatous cells. These tissues act as absorbent layers for nutrients and moisture. Moisture pulled directly from roots is stored throughout the cacti's stems where these tissues reside. A distinct swelling across such an entire cactus is visible after the plant receives a thorough watering or after a rainstorm. Other cacti species have relatively hollow stems that store moisture much like a water bottle. Regardless of the cacti species, each cactus' main goal is water conservation and water storage for long, hot days.

Toxins

• Typical cacti's external spines protect and shade the plants while other kinds of cacti have strategic internal toxins that prevent the plants from being eaten by desert animals. For example, an animal bites into a spineless cactus for hydration purposes. Toxins, such as specific alkaloids, poison the animal and cause frightening and harmful hallucinations. As a result, the animal learns to stay away from that particular cactus for self-preservation. The cactus, in turn, is allowed to flourish and reproduce without constant upheaval from predator feeding habits.

Transpiration

• External spines are truly modified leaves. Their tiny surface area reduces water loss. Cacti, however, still need to photosynthesize with their green epidermis while conserving water. They must open their stomata, or pores, for energy production, but they lose water quickly if that is done during the day. Through crassulacean acid metabolism (CAM), cacti actually close their stomata during the day. They photosynthesize during the daytime using carbon dioxide stored at night. Opening their stomata at night reduces water loss significantly while allowing them to absorb carbon dioxide, a process called transpiration. Without the gas carbon dioxide, cacti could not photosynthesize and thrive.

Drought and Wound Resolutions

• With their slow-growing habit, many cacti are only close to the ground. If they suffer from extreme drought, some species actually contract in size and eventually bury themselves in the soil. Roots and stems effectively reduce their surface area exposed to sunlight and air, which conserves as much water as possible. Additionally, any wounds from weather or animal altercations must be healed quickly to avoid water loss and die-back. Specialized cells producing cork or thick polysaccharides cover the wound quickly, much like a bandage, and stop water loss and possible pathogen infiltration.