. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. THE FLOWER 233 conditions that tend to produce it. If he wishes to develop a dwarf variety, for instance, he will take notice that over- crowding, lack of nourishment, and cold tend to produce that result in nature, and by acting on this hint he can direct his efforts more intelligently. He will learn, too, not to waste time in trying to breed a plant contrary to its nature. He must not expect to gather figs from thistles by any art of selection or skill in culture. By att
. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. THE FLOWER 233 conditions that tend to produce it. If he wishes to develop a dwarf variety, for instance, he will take notice that over- crowding, lack of nourishment, and cold tend to produce that result in nature, and by acting on this hint he can direct his efforts more intelligently. He will learn, too, not to waste time in trying to breed a plant contrary to its nature. He must not expect to gather figs from thistles by any art of selection or skill in culture. By attention to Mendel's law, a still further saving of time and labor may be effected. It is obvious, from what has been said, that a breeder's chance of finding what he wants will be greater in proportion to the number of individual plants he has to choose from. For this reason, a horticulturist sometimes uses thousands and hundreds of thousands of specimens of a single kind in conducting his experiments. In this way he compresses into a short space of time the advantage that nature can gain only by spreading her random experiments over a long series of years, or even centuries. 264. Mutation and variation. — There are at least two ways in which changes in vegetable and animal forms are thought to occur: (1) by the preservation and fixation through selec- tion and heredity, of slight differences that may appear from time to time, such divergences being called "fluctuat- ing variations" ; (2) by the appearance now and then, due to causes as yet unknown, of definite and sudden changes creating a new form at a single, though perhaps small, leap. When such a change is temporary and passes away with the individual in which. Fig. 340. — Mutation in twin ears of corn, showing the sudden variations that sometimes occur, by which a new type may be provided without the labor of Please note that these images are extracted from scanned page images that may have been d
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