360 GENETICS IN RELATION TO AGRICULTURE 



breeders. (8) Stimulus to the work of improvement through the possi- 

 bility of protecting new productions. 



More recently Jones and Hayes have made extensive experiments in 

 crossing commercial varieties of corn upon which they report as follows: 



" Fifty first generation corn crosses have been compared with their parents. 

 Eighty-eight per cent, yielded more than the average and of these 66 per cent, 

 yielded more than either parent. 



" In time of ripening the first generation crosses were on the average interme- 

 diate when compared with their parents. Thus in crosses between varieties 

 differing widely in time of ripening the first generation crosses r>ot only yielded 

 more than the late parent but matured considerably earlier. This increase in 

 the rate of growth is considered to be fully as important under Connecticut 

 conditions as any increase in yield. 



"The highest yielding parents gave the highest yielding crosses as would 

 be expected, but a rather unexpected result was obtained in that there was ap- 

 parently no relation between the yield of the parents and the increase in the 

 yield of the cross. High average yielding parents gave as large increases, when 

 stated in per cent., as low yielding parents. 



"There was a tendency for the crosses whose parents differed in their ability 

 to yield to give the greatest increase. This is also shown by the fact that the 

 dent x flint crosses gave greater increases in growth than the flint x flint crosses. 



"These facts bear out the assumption that hybrid vigor is not the result of 

 an indefinite physiological stimulation but merely the result of the bringing to- 

 gether of greatest number of favorable growth factors. Crosses between va- 

 rieties of diverse type therefore possess a greater total number of favorable 

 growth factors than crosses between similar varieties and hence give larger in- 

 creases when crossed." 



The immediate effect of crossing upon size of the grain and hence on 

 yield should not be confused with the increased production of hybrid 

 plants. There is a popular belief that by planting two varieties in 

 alternate rows the yield will be increased. That this idea is supported 

 by scientific evidence was indicated by the earlier work of Correns, 

 Carrier, and Roberts, but it remained for Collins and Kempton to secure 

 the proof of this important fact. These investigators used the ingenious 

 method of pollinating various white seeded varieties with a mixture of 

 their own pollen and pollen from some variety having colored seeds. 

 By taking advantage of the phenomenon of xenia they were able to make 

 direct comparison of the selfed and the hybrid grains from the same ears. 

 The possible invalidity of their results due to more rapid develop- 

 ment of hybrid grains and consequent repression of selfed grains was 

 removed through the fortunate discovery of an ear that had been twice 

 pollinated, first with its own pollen and a week later with pollen from a 

 colored variety. "All the white kernels were on the lower portion of 

 the ear, all the colored were on the upper portion. Obviously the hybrid 



