Bulletin Volume 254-259 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...material and kept apart. The breeding of new varieties by the selection of superior variations is a task quite different from that of preserving the uniformity of superior strains by selecting for close adherence to type. Varieties are originated by preserving variations, but are preserved by rejecting variations. A thoroughly uniform variety represents a complete suppression of the normal diversity or heterism usually to be found among the members of natural species. Though differences due to external conditions should not be allowed to interfere with the recognition of uniform groups, there is a practical necessity of placing the members of a group as nearly as possible under the same conditions if uniformity of expression is to be judged. The basis of selection to maintain uniformity is not a mere ideal type or artificial standard estab genus, as proposed by Sctauehert in 1897. (Science, n. s.. vol. i, p. 639; see also Bather, F. A., Science, n. s., vol. 32, Dec. 30, 1910, p. 953.) The following new definitions have been offered recently by Dr. G. H. Shull: "Genotype, the fundamental hereditary constitution or combination of genes of an organism." "Blotype, a group of individuals possessing the same genotype." "Pure line, a group of individuals traceable through solely self-fertilized lines to a single homozygous ancestor." In an earlier paragraph is the following explanatory statement regarding pure lines: "There is another prevalent misconception regarding 'pure lines' to which attention needs to be called. The word 'pure' in this connection docs not refer to the genotypic equality of the individuals, but only to the exclusion of all crossing as a source of genotypic differentiation." (See Science, n. s., vol. 35...