CHAPTER IX 



HOW CHARACTERS ARE TRANSMITTED 



Every sp>ecies 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 planted 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 the 

 one unit be com 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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