THE IMPORTANCE OF BROAD BREEDING IN CORN. 39 
other case being 4.6 per cent, while the average increase for the whole 
series of 12 crosses is 16 per cent, running as high as 52.8 per cent. 
If similar increases had been secured by any change in cultural 
methods, experiments to determine the range of applicability of the 
new method would have been promptly inaugurated and the true 
value of the facts ascertained. Although the fact has long been 
established that significant increases can be secured by crossing, we 
are still without knowledge regarding the*conditions necessary for 
this increase. It is to be expected that the increase will be greatest 
between strains that have been closely selected, but there is no direct 
evidence on this point. We should also lose no time in securing 
information regarding the amount of difference that should exist 
between the strains crossed to secure the maximum increase of vigor. 
There is a wide and almost untouched field in this direction that will 
require an enormous amount of experiment and observation before 
justice will have been accorded to this possibility. 
The definite and well-known facts that self-fertilization of corn 
inevitably leads to sterility and that the yield can be increased by 
the crossing of varieties have not been sufficient to attract attention to 
the dangers of inbreeding and close selection. No middle course 
between the ene aerate planting of the general run of seed and 
the rigid selection of a definite type seems to have been seriously 
considered. Had it been realized that diversity is as necessary to the 
life of the species as is chlorophyll to the life of the individual plant, 
it would have been evident that one might as well breed to eliminate 
the green color from the leaves as to suppress this normal variation. 
From a consideration of the habits of the plant the course suggested 
in undertaking the improvement of corn would be to seek the best 
methods for continuing to combine distinct strains, thus utilizing 
the increased vigor and productiveness resulting from their inter- 
breeding. 
While the crossing of our more or less inbred varieties may confi- 
dently be expected to result in increased vigor and fertility, it is 
hardly to be expected that the full amount of the increase in yield 
that follows such crossing can be maintained in future generations. 
The probability is that a part of the increased fertility of the hy- 
brids will prove to be confined to the conjugate generation; that is, to 
the generation immediately following the crossing. In this genera- 
tion male and female elements, representing the two parent varieties, 
are present in the nuclei of the plant, but have not completed the 
process of conjugation, with the result that a sort of protoplasmic 
tension exists, in some way associated with increased vegetative and 
reproductive activity. There is good reason to believe that this is 
2 Cook, O. F., and Swingle, W. T. Evolution of Cellular Structures. Bulletin 
81, Bureau of Plant Industry, U. S. Department of Agriculture. 1905. 
