. Biology and human life. Biology. PLANT BREEDING 505 of another variety (that has not yet been pollenated) and the stigma is then protected from further pollenation. The result- ing seeds are planted, and the new generation is expected to be different in some ways from each of the parents. Any desirable individuals that appear in this generation are kept for further cultivation. This principle has been applied very extensively in the at- tempt to find new and useful variations, among animals as well as among plants (see Fig. 213). ^lanyofthe most valuable domesticated organisms have originate
. Biology and human life. Biology. PLANT BREEDING 505 of another variety (that has not yet been pollenated) and the stigma is then protected from further pollenation. The result- ing seeds are planted, and the new generation is expected to be different in some ways from each of the parents. Any desirable individuals that appear in this generation are kept for further cultivation. This principle has been applied very extensively in the at- tempt to find new and useful variations, among animals as well as among plants (see Fig. 213). ^lanyofthe most valuable domesticated organisms have originated through hybridization. 367. Instability of fluc- tuations. Plants normally differ from each other, even if they are grow^n from seeds in the same fruit. They also differ from each other if they are growm under identical conditions. The differences which re- sult from modification by conditions or environment are called fluctuating varia- tions, or fluctuations, since they flow up and down as conditions change to more favorable or less favorable. Now if we find a few individuals in a plot that are superior to others because they happen to have had somewhat better conditions— moisture, soil materials, protection from parasites or disease— we properly select them for the next crop seed. But will the next crop be as much better than this year's as our seed plants were. Fig. 213. Wheat varieties and their hybrid At left, head of "bearded" wheat: at right, head of "beardless"" wheat; in middle, head of wheat resulting from a cross of the other two types, grown at the Minnesota Agricul- tural Experiment Station. (From Bergen and Caldwell's "Practical Botany"). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gruenberg, Benjamin C. (Benjamin Charles), 1875-1965. Boston, New Yo
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