534 HEREDITY 



individual plant and animal inherits much that does not express 

 itself. In the study of heridity, not only resemblances but also 

 the differences due to inheritance and the latent factors must be 

 considered. 



Mechanism of Heredity. — It is obvious that parents do not 

 transmit their characters to their offspring, but transmit some- 

 thing that causes similar characters to develop in their offspring. 

 They do not transmit a long nose, black eyes, red hair, etc., to 

 their children but transmit something that causes such features 

 to appear in their children. Likewise, Flint Corn does not 

 transmit flinty endosperm to its offspring, but transmits some- 

 thing that causes the endorspern of its offspring to be flinty. 



The substance transmitted from one generation to the next is 

 protoplasm. In one celled plants and animals, like the Bacteria 

 and Protozoa, the new individuals are formed by the division of 

 the parent, each half of the parent becoming a new individual. 

 The new individuals inherit the protoplasm of their parents. 

 This protoplasm which the new individuals inherit has a more or 

 less fixed way of expressing itself throughout generations, and 

 consequently the new individuals develop the features of the 

 parents due to the protoplasm they inherited. 



In the sexual reproduction of the higher plants and animals, 

 each generation inherits from the preceding one protoplasm in 

 the form of sperms and eggs. Sperms and eggs apparently share 

 equally in determining the characters of the offspring. Since a 

 sperm in most cases is httle more than a nucleus, it is obvious 

 that the substance having to do with determining characters is 

 a nuclear substance and is supposed to be the chromatin of the 

 nucleus. The behavior of the chromatin in such a regular way 

 during cell division suggests that it has a very vital relation to 

 heredity. As to the nature of the chromatin substance respon- 

 sible for the development of characters and as to how it works, 

 we have only theories. 



Gemmules, Determinants, and Genes. — Students of heredity 

 hold the idea that the development of characters in an individual 

 depends upon minute bodies or particles which the cells of the 

 individual have in their organization. Certain particles deter- 

 mine the color of the hair, others the color of the eyes, others the 

 height, and so on. Each generation inherits from the preceding 

 generation groups of these character-determining particles which 



