Cactus
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dioxide chemically linked to malic acid until the daytime. During the day the stomata are closed and the plant releases the stored CO2 and uses it for photosynthesis. Because transpiration takes place during the cool humid night hours, water loss through transpiration is significantly reduced. Some cactus flowers form long tubes (up to 30 centimetres) so that only moths can reach the nectar and therefore pollinate the blossoms. There are also specializations for bats, hummingbirds and particular species of bees. The duration of flowering is very variable. Many flowers, for example those of Selenicereus
Reproductive ecology
grandiflorus (Queen of the Night) are only fully open for two hours at night. Other cacti flower for a whole week. Most cacti are self-incompatible, and thus require a pollinator. A few are autogamous and are able to pollinate themselves. Fraileas only open their flowers completely in exceptional circumstances; they mostly pollinate themselves or others with their flowers closed ("cleistogamy"). The flower itself has also undergone a further development: the ovary tends to become a completely protected area, protected by thorns, hairs and scales. Seed formation is very prolific, and the fruits are mostly fleshy, pleasant tasting and conspicuously coloured. Goats, birds, ants, mice and bats contribute significantly to the spreading of the seeds. Because of the plants' high water-retention ability, detached parts of the plant can survive for long periods and are able to grow new roots anywhere on the plant body. Among the remains of the Aztec civilization, cactus-like plants can be found in pictorial representations, sculpture and drawings, with many depictions resembling Echinocactus grusonii. Tenochtitlan (the earlier name of Mexico City) means "place of the sacred cactus." The coat of arms of Mexico to this day shows an eagle perched on a cactus while holding a snake, an image which is at the center of the Aztec origin myth. Economic exploitation of the cactus can also be traced back to the Aztecs. The North American Indians utilize the
History