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5 micron wide to seaweeds which may be several hundred feet long, and California redwoods, some of which attain heights of over 350 feet, diameters of 30 feet and weights of 2100 tons (these redwoods are the tallest known land plants). In most cases, each species has a characteristic average size range, but plants are exceedingly susceptible to environmental conditions and individuals are often larger or smaller, depending upon the nature of surroundings in which they have grown.
The forms of plants vary even more than do their sizes. As we shall presently see, there are 340,000 distinct species with numerous varieties. Each species has its own characteristic habit of growth, shape of leaves, method of branching, form, and colour of reproductive structures and other peculiarities which give it a personality of its own. Some plants are trees, others are woody vines, some are herbaceous (soft-stemmed) vines, still others are erect herbs. Some have large leaves, some have small leaves, some have leaves with toothed or otherwise indented margins, while some are with smooth margins. Some have no leaves but consist entirely of stems, roots, and flowers; others have simple bodies not differentiated into roots, stems, leaves or flowers.
Some plants (desert plants for example) grow very slowly, so slowly that any increase in heir size is noticeable only if ihey are examined at intervals of several years. In tropics, however, growth frequently proceeds at incredibly rapid rates. These are extremes. All green plants manufacture sugar by the process of photosynthesis, but they utilise this sugar in different ways. Some convert them into fatty substances which they store in their tissues; others transform them into starches as storage of foods. Some plants elaborate large quantities of organic acids-citric acid in lemons and oxalic acid in rhubarbs. Some manufacture aromatic oils—dill, caraway, spearmint, sassafras, lavender, peppermint etc.
Another physiological difference among plants is found in their longevity. Bacteria live for 20 or 30 minutes and form two new organisms, which in turn form offspring of their own. At the other extremes of age are certain coniferous trees, such as California redwoods which attain ages over 3000 years. Many wild and cultivated plants are annuals, which live but a singlegrowing season, some are biennials, which live through two
—: 18:Jain Education International
JAIN BIOLOGY
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