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Encyclopedia Britannica - Main :: BUN-CAL |
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CACTUS . This word, applied in the form of KhKros by the ancient Greeks to some prickly plant, was adopted by Linnaeus as the name of a group of curious succulent or fleshy-stemmed plants, most of them prickly and leafless, some of which produce beautiful flowers
The Cacti may be described in general terms as plants having a woody axis
tissue forming the fleshy stems. These are extremely various in character and form, being globose, cylindrical, columnar or flattened into leafy expansions or thick joint -like divisions, the surface being either ribbed like a melon, or developed into nipple-like protuberances, or variously angular, but in the greater number of the species furnished copiously with tufts of horny spines, some of which are exceedingly keen and powerful. These tufts show the position of buds, of which, however, comparatively few are developed. The stems are in most cases leafless, using the term in a popular sense; the leaves, if present at all, being generally reduced to minute scales. In one genus, however, Peireskia, the stems are less succulent, and the leaves, though rather fleshy, are developed in the usual form. The flowers
o-a 000 QU"~OOO- Opf000 t, Flower reduced; 2, Same in vertical section; 3, Flattened branch much reduced; 4, Horizontal
increase in size upwards, and at length become crowded, numerous and petaloid, forming a funnel-shaped blossom, the beauty of which is much enhanced by the multitude of conspicuous stamens which with the pistil occupy the centre. In another group, represented by Opuntia (fig. I), the flowers are rotate, that is to say, the long tube is replaced by a very short one. At the base of the tube, in both groups, the ovary becomes developed into a fleshy (often edible) fruit, that produced by the Opuntia being known as the prickly pear or Indian fig. - The principal modern genera are grouped by the differences in the flower - tube just explained. Those with long - tubed flowers comprise the genera Melocactus, Mammillaria, Echinocactus, Cereus, Pilocereus
minor importance. Cactaceae belong almost entirely to the New World; but some of the Opuntias have been so long distributed over certain parts of Europe, especially on the shores of the Mediterranean and the volcanic soil of Italy, that they appear in some places to have taken possession of the soil, and to be distinguished with difficulty from the aboriginal vegetation. The habitats which they affect are the hot, dry regions of tropical America, the aridity of which they are enabled to withstand in consequence of the thickness of their skin and the paucity of evaporating pores or stomata with which they are furnished,these conditions not permitting the moisture they contain to be carried off too rapidly; the thick925fleshy stems and branches contain a store
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