360 (ENETICS 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. : 
“Tn 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 not 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 
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