. Heredity and evolution in plants . he dawnof plant life to the present. Hence, until we know thelaws of heredity, we cannot fully understand expression,reproduction, development, variation, sex, or evolution. 2. To Applied Science.—Correct ideas concerning he-redity are absolutely essential to such phases of appliedscience as animal and plant breeding. In the light of suchknowledge the breeder can avoid making useless experi-ments, and can accomplish desired results more quickly,more cheaply, and with greater certainty of success. 3. To Man.—A correct knowledge of the principles ofheredity i
. Heredity and evolution in plants . he dawnof plant life to the present. Hence, until we know thelaws of heredity, we cannot fully understand expression,reproduction, development, variation, sex, or evolution. 2. To Applied Science.—Correct ideas concerning he-redity are absolutely essential to such phases of appliedscience as animal and plant breeding. In the light of suchknowledge the breeder can avoid making useless experi-ments, and can accomplish desired results more quickly,more cheaply, and with greater certainty of success. 3. To Man.—A correct knowledge of the principles ofheredity is vital to mankind; no knowledge is more so. Torealize this, we have only to reflect that our own charactersare very largely the result of inheritance from our ances-tors; and not only our characters, but our physical char-acteristics, our vigor of mnd and body, our capacity foreducation, our susceptibility to disease, and often theactual existence of some disease within our bodies or minds. 45 1IKRKDITY AND INVOLUTION IN PLANTS. 37. Heredity Reduced to Its Lowest Terms.—We may study heredity under the very simplest conditions in thedescent of one-celled organisms, such as plant, a unicellular green alga, is a globule of proto-plasm, containing chlorophyll, and surrounded by acellulose cell-wall (Fig. 33). But why is it globular, why does it contain chlorophyll, why hasit a cell-wall of cellulose? Why isit not elliptical, why is it not red in-stead of green, why does it have acell-wall, instead of existing nakedlike the plasmodium of a slime-mold, why is its cell-wall of cellulose,rather than of lignin or chitin? The short answer is, because itsancestors, for ages and ages, have FIG. 33.— Individualplants of green slime POSSessed the characteristics which (Pleurococcus vulgar is) now characterize Pleurococcus showing the tendency of plants. But that only puts the the cells to remain question back an indefinite number attached after cell-divi-sion, thus
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