CHAPTER IX 
HOW CHARACTERS ARE TRANSMITTED 
Every species of its own kind- The machinery of transmission - Fertiliza- 
tion - Fertilization in general. The material transmitted - Chromosomes - 
Development, or growth and differentiation - Termination to growth 
The facts brought out in the last chapter show that many of 
the differences between individuals arise from variability in the 
degree of development of a single character, and that much 
opportunity for improvement lies in this field of selection. 
There is, however, another and a greater cause of individual 
differences, and that is in the particular unit characters present. 
For example, everybody would recognize that there is more dif- 
ference between a small draft horse and a racer than between 
the small drafter and a larger one of the same type. 
This brings us to a study of the transmission of unit char- 
acters with a view to their control between parent and offspring 
for the purposes of improvement. The manner of this trans- 
mission, it will be seen, is the controlling factor in heredity and 
affords the principal basis for improvement. 
Every species of its own kind. In a later chapter heredity 
and environment will be discussed, but here it is sufficient to 
call attention to the very large and obvious fact that whatever 
the influence of environment, the differences between individ- 
uals are not only great but inherent. 
A kernel of corn and a kernel of wheat may be slanted side 
by side in the same soil. If the soil be fertile and the season 
favorable, the crop will be good. If, on the other hand, the soil 
be poor or the season bad, then the crop will be small, but ie 
one will be corn and the other wheat in either case, all of which 
is but another way of saying that the real nature of the plant or 
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