. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. UTILIZATION OF IIYBRWS IN PLANT BREEDING 355 until 1908 and in that year "the general environmental conditions were much above normal. For opposite reasons, poor soil and badly distributed rainfall, the yields of 1909 are somewhat too low and the yields of 1911 are very much too ; With these facts in mind an examination of the table shows that the strains became more and more differentiated as to yield as inbreeding progressed. "The first strain, No. 0, is a re- markably good var
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. UTILIZATION OF IIYBRWS IN PLANT BREEDING 355 until 1908 and in that year "the general environmental conditions were much above normal. For opposite reasons, poor soil and badly distributed rainfall, the yields of 1909 are somewhat too low and the yields of 1911 are very much too ; With these facts in mind an examination of the table shows that the strains became more and more differentiated as to yield as inbreeding progressed. "The first strain, No. 0, is a re- markably good variety of corn even after five generations of inbreeding. It yielded 80 bushels per acre in 1910. ... In the field, even in 1911, the plants were -uniformly vigorous and healthy and were especially remarkable for their low variability. The poorest strain. No. 12, is partially sterile, never fills out at the tip of the ear and can hardly. Fig. 148.—Inbred strains of Learning dent corn compared with Fi and F2 hybrid gener- ations. The yields per acre were as follows: No. 9 (at the left) bu.; No. 12, bu.; (12 X 9)Fi, 117,5 bu.; (12 X 9) i^2, bu. {After East and- Hayes.) exist alone. . When two of these inbred strains are again crossed, the Fx generation shows an immediate return to normal vigor. The plants are earher and taller, and there is a greater total amount of dry matter per plant. For example, in 1911 the average height of all the strains of inbred Learning dent was 84 inches while the average height of the 16 hybrid combinations was 111 inches and the height of the shortest hybrid combination was 1 foot greater than that of the tallest inbred ; In general it seems that the combinations into which strain No. 7 was introduced were the best while those in which the poorest strain. No. 12, was used were the poorest. However, a cross between these two strains in 1911 yielded bushels per acre. The Fs genera- tion from a number of the crosses was
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