From Seed to Seed:
Plant Science for K-8 Educators

Adaptations for water. Anchored in one place, plants can't travel to search for life-sustaining water. Plants growing in regions where water is scarce or available only during a brief rainy season have adopted various strategies for survival. Let's voyage into a desert, and look at the various strategies for survival in an environment where water is in short supply.

• Succulent stems allow cacti to store water. The barrel cactus has an accordion-like stem that allows the cactus to swell as the roots take in water during a rainy spell, then shrink as the moisture is used up.
  
  
• The spines on a cactus perform a number of important functions. They help to shade the plant from intense sun, helping to cool the surface. And, if you've ever bumped into a cactus by mistake, you know that they also serve as protection.
  
  
• An extensive, shallow root system allows cacti to take advantage of even the lightest rainfall.
  
  
• During the hot, dry summer, many desert plants drop their leaves and become dormant. Cactus spines are modified leaves; photosynthesis takes place in the stem and can continue throughout the summer. With no leaves, the surface area exposed to the sun and drying winds is reduced, which in turn reduces water loss from transpiration.
  
  
• Cacti have a waxy cuticle layer that helps seal in moisture.

• The desert lily's bulbs are found at a depth of 12 to 18 inches. The plant can lie dormant for years until adequate water is available.
  
  
• Welwitchia, a desert gymnosperm, absorbs water from the nighttime fog through its leaf stomata.
  
  
• The creosote bush has a far-ranging root system: roots may reach 75 feet in length.
  
  
• Some plants complete their life cycles in months, or even weeks. Desert sand verbena seeds germinate in the spring after the winter rains. They grow quickly, bloom, and produce and scatter seeds, then die with the onset of summer heat. The seeds are extremely durable and drought-resistant, and may lie dormant for years until conditions are favorable for germination. Plants that bloom for a brief time in the spring are often referred to as ephemerals.

Orchids have aerial roots that can absorb atmospheric water vapor.

Bromeliads grow in tree branches; their leaves grow in cup-shaped rosettes that collect rainwater.

Closer to the home front, you have probably seen a dull, powdery, bluish-white coating on various fruits, including plums, apples, and grapes. This natural surface wax, called a "bloom," is easily wiped off. Other plants with a noticeable bloom include some succulents and cacti; also the leaves of carnations and cabbages (especially red cabbage). Although all plants have a cuticle layer, this visible bloom occurs when the surface wax occurs in tiny "rodlets" that protrude from the surface cells. Like all cuticles, the bloom helps conserve water by reducing evaporation from surface tissues. The word glaucous is used to describe plants with a visible waxy bloom.