170 HAROLD H. SMITH 



Results of Selection 



The result of selection for tall plants with many, large leaves can be seen 

 by comparing the means of Al with those of the parental and hybrid genera- 

 tions in Tables 10.1 and 10.2. 



From the 1947 data it is evident that in the F4 generation of selection Al a 

 significant increase had been obtained over the parents and Fi's in plant 

 height and green weight. This was accompanied by a lengthening in time 

 required to reach maturity. With regard to this latter character, it was noted 

 that the average time for reaching maturity in five of the six Fi's was later 

 than the average of their respective parents. This is contrary to the usual 

 result in first generation hybrids of certain other plants, as maize and toma- 

 toes; and, where early maturity is an important economic character, would 

 generally not be considered a manifestation of hybrid vigor, at least in a 

 "beneficial" sense. 



The number of leaves in selection Al was significantly higher (P < .05) 

 than in any of the Fi's, and all but the most vigorous parent, Olson 68. Leaves 

 of the selection were shorter than the parent with the longest leaves (Olson 

 68), not significantly different from the three Fi's that involved this parent, 

 and longer than in the other three parents and three Fi's. 



The 1949 data (Table 10.2) corroborated the 1947 results. There was a 

 significant increase (P ^ .01) in plant height and in number of nodes over 

 the two main parents and their Fi. Number of nodes, rather than of leaves, 

 was used since it is a more reliable criterion of the same character. As in 

 1947, there was a less marked effect of selection on leaf length, though there 

 appeared to be an increase in Al from the F4 to the Fe. For this character 

 the selection was superior to 34753 and the Fi, but not significantly different 

 from Olson 68, although a close approach to significance at the 5 per cent 

 level of probability was reached. 



The total within plot variances of selection AKFe) for plant height, num- 

 ber of nodes, and leaf length were in no case significantly higher than for the 

 more variable parent. It was deduced, therefore, that the inbred selection 

 had reached relative homozygosity. 



The general conclusions were that an inbred selection had been produced 

 which had increased plant height, more nodes, heavier green weight, and a 

 longer growth period than any parent or Fi. Length of leaf had been main- 

 tained at least at the level of the best parent variety. 



It was also noted, though no quantitative data were taken, that selection 

 Al had markedly less vigorous sticker growth at topping time than any of the 

 other varieties or hybrids. This is an important agronomic character. 



Heritability and Gain 

 One of the objectives in conducting these experiments was to attempt to 

 determine to what extent the progress realized in actual selection experi- 



