Orchid Growing Training Course
Like orchid fanciers, many people vie to have collections of cacti with as many different species (or names) as possible. Vast numbers of plants of Echinocactus, Echinocereus, Epiphyl-lum, Gymnocalycium, Mammillaria, and Rebutia are propagated commercially in nurseries, especially in southern California, Arizona, and New Mexico. Cactus nurseries produce wonderful specimens in short periods of time, making the industry a profitable one. Many nurseries distribute catalogs of their current offerings as well as selling specimens locally. Several million plants are produced annually worldwide.
This species is common above La Guayra and about Puerto Cabello, Venezuela, especially about the latter place, where it is the most common cactus seen, being abundant both on the hills and on the flats near the sea. Its branches are often overrun by orchids, vines, and bromeliads.
The great majority of cacti carry out the special photosynthetic process called crassulacean acid metabolism (cam), a phenomenon also found in the stonecrop family Crassulaceae, an unrelated family of succulents, and other plants that must cope with a limited supply of water, including agaves, yuccas, bromeliads, and many orchids (Mauseth 1991,268-269). It is a kind of photosynthesis that minimizes the use of water by the plant.
Many think of Epiphyllum and orchid cactus as synonymous, but orchid cacti are now placed in Schlumbergera or Diso-cactus, closely related genera in the same tribe, Hylocereeae. One encounters numerous so-called epiphyllum hybrids, which in fact rarely involve species of Epiphyllum as a parent. Rather, these magnificent plants, bearing shimmering, iridescent flowers, are mostly hybrids of related genera such as Disocactus, Pseudorhipsalis, and Selenicereus.
The flowers of the Stapelieae are structurally the most complicated in all succulents, and show a high level of evolution comparable to that of the orchids, with which this group shows certain evolutionary parallels. In explaining the structure of the commonest species, Orbea (Stapelia) variegala (19.7), it will help to have in view the diagram of a simple flower of Crassula (2.18) in order to understand the ways in which the consecutive whorls of floral parts have been transformed. In a flower such as Crassula. each anther is two-lobed and splits vertically to shed a cloud of dust-like pollen on either side. This is not so in Stapelieae. The contents of each anther lobe remain stuck together, and each pair of pollen bodies is linked by a yoke bearing two wing-likeappendagesorcarriers. Wecall such an organ a pollinium, and it has a counterpart in the orchid Family.
Difficulties of defining a succulent make the limits of our subject somewhat elastic. Some would include the halo-phytes, and some the yuccas, which show fleshiness of a sort in their stems although many are hardy enough to withstand frost. Others would include orchids (several of which qualify on all counts) and bromeliads members of the pineapple Family now so popular as house plants. To include such plants would broaden the scope of this book considerably, and these two large and highly individual Families are more suitable for specialist treatment by themselves. stage has been occupied by orchids, ferns, palms and other novelties as fashion dictated. Now, however, there are succulent plant societies (usually burdened with the tiresome tautonym Cactus and Succulent Society of ) in America. Europe. South Africa. Australia. New Zealand and Japan. The demand for plants keeps many nurseries, large and small, in business indeed, the drain upon habitats to supply imported plants has...
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