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Plant Family: Almost one fourth of the earth's vegetation cover is in grasslands—the great prairies and plains of North America, the extensive pampas of South America, the steppes of Asia, and the velds of Africa. At least 7,000 species of grasses are known. The grass family (Gramineae) is outranked in number of species only by four other families-the bean family (Leguminosae), daisy family (Compositae), coffee family (Rubiaceae) and orchid family (Orchidaceae). But in numbers of individual plants spread over the globe, the grasses are unsurpassed. They have a wider range than any other plant family except for lichens and algae.
The tallest trees measured, kempas (Koompassia excelsa), in Sarawak, were 275 feet high. A single plant family, the lauan or dip-terocarp family (Dipterocarpaceae), though absent from the New World, is by far the commonest, often producing half of the timber volume. The legume family, among many others, is well represented. Hawaii too has areas of tropical rain forest in which tree ferns are conspicuous.
It is the gardener's task to make use of the weather as much as possible. Temperature directly influences the rate of plant growth. The fastest growth will take place at the higher temperature limits of an individual plant's tolerance. A plant classified as tender will not endure temperatures below 32°F (0°C). A half-hardy plant can stand a few degrees of frost, but not a cold winter. By contrast, a hardy plant can tolerate considerable cold. Naturally, the degree of hardiness varies from plant to plant. How well a plant grows in an area depends largely on its native climate and on how easily it can adapt to its new environment.
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