ACTIVE AND LATENT GENES 535 



are transmitted in the eggs and sperms. Different names have 

 been given to these particles and different ideas concerning their 

 nature have been held. 



Charles Darwin called them gemmules. His idea was that 

 every cell of an individual has the power to form gemmules and 

 gemmules are formed for every pecuUar trait an individual has. 

 For example, if the epidermal cells of a plant are induced by 

 drought to develop hairs, then the epidermal cells also develop 

 gemmules for this character. He supposed these gemmules cir- 

 culate through the body of the plant or animal and finally reach 

 the sperms and eggs. The sperms and eggs of an individual, 

 therefore, not only have the gemmules of previous generations, 

 but also gemmules for those peculiar traits not inherited but 

 developed in response to environmental influences. This means 

 that an individual transmits to its offspring not only what it 

 inherited but also what it acquired. However, later investiga- 

 tions show that acquired characters are seldom, if at all, inherit- 

 able. 



Weismann (1834-1914) called these character-determining par- 

 ticles determinants. His idea was that they are the chromatin 

 particles of cell nuclei and that they are transmitted from parents 

 to offspring in the nuclei of sperms and eggs. He thought the 

 modifications that environment causes in a plant or animal have 

 httle or no influence on the number of determinants in the sex 

 cells. There are no determinants added to the sex cells to repre- 

 sent them. In other words, acquired characters are not inherit- 

 able, and this idea is most in accord with recent experiments. 



The most recent investigators refer to the character-determin- 

 ing particles as genes, and also consider them chomatin particles. 

 In cell division they are distributed to the new cells in the form 

 of chromosomes. 



Active and Latent Genes. — In -each plant and animal there 

 are many genes that do not function in causing characters to 

 develop. They are called latent genes, while those that function 

 are called active genes. Latent genes are transmitted the same as 

 active ones and usually in some future generation become active. 

 Also some active genes become latent in future generations. 



Heredity and Environment. — As to what characters will 

 develop in an individual, that depends upon what the individual 

 inherited and also upon its surroundings. A plant may have 



