CHAPTER XXIII 



HEREDITY 



General Features of Heredity 



Nature of Heredity. — The constancy of species of plants 

 and animals through successive generations depends upon the 

 fact that the individuals of each generation are fundamentally 

 like their parents. Thus the offspring of Sweet Corn have the 

 characters of Sweet Corn, and the offspring of Flint Corn have 

 the characters of Fhnt Corn. Even when parents differing in 

 one or more fundamental characters are crossed, the characters 

 of both parents will appear somewhere in future generations. 

 The transmission from parent to offspring of similarities in 

 structure and function is heredity. But heredity means more 

 than the transmission of similarities. In the study of varia- 

 tions it was learned that no two individuals are alike, and hence 

 offspring, although fundamentally similar and like their parents, 

 always have individual differences. Thus every plant or ani- 

 mal, besides resembling its parents, brothers, and sisters, has its 

 own peculiar features which give it individuality. In a field of 

 a given variety of Corn, although the plants have the characters 

 of the parent variety, they differ in height of stalk, length and 

 shape of ear, depth of kernel, time of maturing, and in many 

 other ways. Most of these differences are fluctuating varia- 

 tions, while some may be due to something inherited. In the 

 study of heredity not only the resemblances but also the differ- 

 ences must be accounted for. Heredity means the transmission 

 of fundamental resemblances with differences in detail. 



The Physical Basis of Heredity. — It is obvious that parents 

 do not actually transmit characters to the offspring, but trans- 

 mit something that causes the characters to appear in the 

 offspring. For example, a red flowered Sweet Pea does not 

 transmit a red color to the flowers of its offspring, but transmits 

 something through the sperm and egg that causes a red color 



