Oct. IS, 1914 First-Generation Maize Hybrids 89 



branching may result in a decreased yield. Hence, if some hybrids show 

 reduced yields, this fact alone should not be taken as proving an excep- 

 tion to the general rule that the first generation of a hybrid shows 

 increased vigor. 



The method of comparison here used brings the plants into close com- 

 petition, and it may be urged that the differences between the kinds are 

 as a result unduly accentuated. With a view to detecting a possible 

 effect of competition, the yield of the plants in hills with four plants was 

 compared with plants of the same varieties in hills with less than four 

 plants. 



In P9, P19, and Phgy the j'ield per plant was slightly higher in the 

 4-plant hills than in the 3-plant hills. The differences were, however, 

 insignificant. In Phge the yield of the plants from the 3-plant hills 

 exceeded that from the 4-plant hills by 67 grams per plant. The number 

 of 3-plant hills was so small, however, that little confidence should be 

 placed in the difference, which was but three times the probable error. 



An attempt was made to secure a more accurate comparison by cor- 

 recting for the differences in the yield of the different kinds, thus making 

 it possible to compare the yield per plant of all the 4-plant hills with that 

 of all the 3-plant hills. The average yield per plant in the 4-plant hills 

 was 211 ±7 grams. The average yield of the 3-plant hills was 227 ±10. 

 The difference of i6±i2 grams is therefore not significant. 



With such a large experimental error it is of course not impossible 

 that the crowding of the plants has a tendency to reduce the yield, but 

 if so the difference is too small to be measured by the means employed, 

 If crowding operated to accentuate differences, it might also be expected 

 to retard the date of flowering. The average number of days to flowering 

 was, however, the same in the 4-plant hills and in the hills with less than 

 four plants, being 72.4 days in both. Thus there is no evidence that 

 the growing of the four kinds close together affects the relative yield of 

 the kinds, and when ample space is provided between the hills, viz, 

 4 by 5 feet, as in this experiment, it is believed that this source of inac- 

 curacy is insignificant. 



The conditions of the experiment here reported constitute a severe test 

 of the method of comparison by individual hills. The kinds tested were 

 very dissimilar, while the soil of the experiment was unusually uniform. 

 The gain in accuracy secured by using the hill as the unit of comparison, 

 instead of averaging the yield of all the plants of a kind, may be measured 

 by a comparison of the standard deviations or the coefficient of variability 

 observed when the yields are compared by the two methods. 



When the yield of each plant was compared with the average of all the 

 plants of the same kind, the coefficient of variability was 5.42±o.i7. 

 When the yield of each plant was compared with mean yield of the hill in 

 which it grew the coefficient of variability was 5.o5±o.i3. There is, 

 thus, a slight gain in accuracy, notwithstanding the exceptional uni- 

 formity of the soil where the experiment was tried. With less uniform 

 soil conditions the advantages secured by making the comparison on the 

 basis of individual hills would increase. 



The dates when the first staminate flowers opened and when the first 

 silks appeared were recorded for all the plants. The average mmiber of 

 days from planting to flowering is shown in Table II. 



60300°— 14 7 



