PREVIOUS EXPERIMENTS WITH FIRST-GENERATION HYBRIDS. 19 



very fair indication of the comparative vigor of each strain was obtained. Unfor- 

 tunately crows and chipmunks played havoc with the "stand " in a number of cases, 

 and accurate figures can not be given except in the following four cases where the 

 stand was perfect. 



A white dent, No. 8, yielded 121 bushels per acre (at 70 pounds per bushel); a 

 yellow dent, No. 7, which had been inbred artificially for three years, yielded 62 

 bushels per acre; the cross between the two varieties, No. 7 X No. 8, yielded 142 

 bushels per acre. 



Longfellow, No. 34, an 8-rowed, yellow flint, yielding 72 bushels per acre, was 

 crossed with the same No. 8 white dent, yielding 121 bushels per acre; the resulting 

 cross yielded 124 bushels per acre. 



Sturges's hybrid, a 12-rowed, yellow flint with a tall, nonbranching stalk, partaking 

 of the characters of dent varieties, was also crossed with No. 8 white dent. The flint 

 parent yielded 48 bushels per acre, while the cross yielded 130 bushels per acre. 



Two families of a yellow dent variety, which had each been inbred artificially for 

 three years, were the parents of the fourth cross. No. 12, yielding 65 bushels per 

 acre, was crossed with No. 7, yielding 62 bushels per acre. The Fj generation yielded 

 202 bushels per acre. This last result is somewhat distorted, as five stalks per hill of 

 the cross were allowed to grow, while of the parents only four seeds per hill were planted. 

 About 90 per cent of the seeds produced mature stalks. Notwithstanding the close- 

 ness of planting to which this cross was subjected, however, casual observation was 

 sufficient to show that it soared far beyond each parent in vigor of plant and size of ear .a 



For ease in comparison Doctor East's results are here given in 

 tabular form: 



White dent X yellow dent. 

 Yellow dent X white dent. 

 Yellow flint X white dent. 

 Yellow dent X yellow dent 



Yield of 

 female 

 parent. 



Bushels. 



121 



72 



48 



65 



Yield of 



male 

 parent. 



Bushels. 



62 

 121 

 121 



62 



Average 

 yield of 

 parents. 



Bushels. 

 91.5 

 96.5 

 84.5 

 63.5 



Yield of 

 hybrid. 



Bushels. 



142 



124 



130 



*161 



Percentage 

 of increase 



over 



average of 



parents. 



Per cent. 



55 



28. 



54 



154 



* This is the cross of which Doctor East states that five stalks per hill were allowed to grow instead of 

 four, as in the case of the parents. The yield is here reduced by one-fifth from the original figure of 202 

 bushels to allow for the additional number of hybrid plants that were grown, although by this calcula- 

 tion the hybrid is placed at a disadvantage, due to the closeness of the planting. 



It will be noted that the comparison with the parents was in this 

 case very accurate, the plants representing the parents being grown 

 from the identical ears that were used to make the crosses. The 

 yield of one of the parents in the first cross and both the parents in 

 the fourth had, how^ever, been depressed by self-fertilization for three 

 successive years. It is interesting to note in this connection that the 

 introduction into a cross of an inbred strain yielding only one-half 

 that of the other variety here results in increasing the yield above 

 that of the high-yielding parent by over 17 per cent. Furthermore, 

 the highest yield in the experiment was secured from a cross between 



«East, E. M. The Distinction between Development and Heredity in Inbreeding. 

 The American Naturalist, vol. 43, no. 507, 1909, pp. 178-179. 

 191 



