Author: Edward Murray East

Publisher: Theclassics.Us

Published: 2013-09

Total Pages: 72

ISBN-13: 9781230314754

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 edition. Excerpt: ...starts off poorly, as shown in the accompanying illustration (Fig. 33), but soon catches up and passes the second generation. At maturity the second generation is shorter and less productive, although it has a much greater variability. The third generation from selfed plants of this particular cross has been grown, and there is still further loss of the stimulation which is at its maximum in the first generation. On continued inbreeding these families presumably would exhibit a continuation of the same course of reduction in size, vigor and variability shown in the original inbreeding experiment, until homozygosity was again 100 78 50 29 Sronth Curres of Two Inbred Strains ef Maize and Their Fj and F2 Hybrids. 30 40 50 Gf 7 8 Wumlaer of Days from Planting 9 33.--Qraphs showing growth curves of two inbred strains'of maiie and thier first and second generation hybrids. reached. The resulting inbred strains would have about the same amount of development as the original inbred strains, but would probably differ from them in appearance through the possession of different combinations of characters. The principal point is that the vigor and size lost by inbreeding are immediately restored by crossing, but lost again on further inbreeding. It is a transitory effect, for the most part, impossible of fixation. Increases in yield of grain are also frequently obtained when ordinary commercial varieties of maize are crossed. Earely are the increases greater than 10 per cent., however, and even this is more commonly to be expected when varieties of somewhat different type are used; for example, flint and dent. Most varieties of corn are now so widely crossed and furthermore are so near the limit of production that great advances are not...