Page 39 - Reading and Writing 6

Listen and Read

The Cactus Plant

Cacti are plants that thrive in hot and arid desert areas and can survive long
periods of drought. Cacti are well adapted to survive in times of water scarcity. The
groundwater level in the desert is very low, and rainfall, too, is very rare; thus, the
adaptations of the cacti also allow them to collect, conserve, and store water for
long periods. The green, hard-walled, swollen stem of the cactus holds a pigment
called chlorophyll that performs the process of photosynthesis and produces food for
the plant.

A cactus can have an arborescent (tree-like), cylindrical, rounded, irregular, or
starfish shape. Its surface can be flat or covered with ridges. The succulent stem
stores water within itself, and its waxy coating prevents the transpiration or loss of
water from the plant. In a cactus, the leaves have been modified into small spines
or scales. Unlike other plants that have leaves, the small surface area of the cactus
spines or scales does not allow them to lose water through evaporation. These
spines also protect the plant from predators that may want to eat it. Cactus spines
can be used in the production of hooks, combs, and needles. Many types of cactus
have long, fibrous roots to absorb water from the soil, while some have shorter and
more compact roots that can absorb dew water that falls from the plant. Water
from a cactus has a higher density than tap water, but it is safe for drinking.

Cacti have dormant periods and times of intense growth and blossoming. Periods
of growth require adequate water and sunlight, and they are usually shorter in
duration than periods of rest. The tallest free-standing variety of cactus is the
Pachycereus pringlei. Its biggest recorded height has been 19.2 metres. The smallest
free-standing cactus variety is the Blossfeldia liliputana, which grows to only about
one centimetre in diameter at maturity. Cacti can survive from 15 to 300 years,
depending on species.

Overcollection and habitat loss are major threats to the survival of cacti in the wild.
Certain species are listed as endangered, but, luckily, the law prohibits the trade of
most species of cacti.

After You Read

1 Work with a partner and discuss the following questions.

1 What do you think is the best feature of a cactus? Why?

2 How might cacti help a person or an animal to survive the desert?

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