GENES AND CHARACTERS 323 



of somatic cells. Lillic summarizes modern knowledge of this 

 subject in a recent article and concludes that "we have no present 

 working hypothesis effective in this most fundamental aspect of 

 the life history." 



According to modern views the complex of genes which is present 

 in the zygote is carried into all cells of the body. The differentia- 

 tion of the cytoplasm which gives rise to the multitude of special- 

 ized adult cells is therefore not accompanied by nuclear differentia- 

 tion of equal degree. In spite of this fact there is evidence that 

 the genes are active at various periods of life in connection with 

 cytoplasmic differentiation for adaptation to definite environ- 

 mental conditions. The ability to become tanned, for example, 

 is inherited although it does not become operative until the proper 

 environmental stimulus is received. 



Goldschmidt has attempted to explain this interaction by two 

 theories, one of which assumes that the genes are so conditioned 

 that they enter into activity at a definite rate and time for each, 

 while the other suggests that the genes act only with specific 

 cytoplasmic materials. As Lillie points out, the latter assumes 

 cytoplasmic differentiation as a condition for activity of the 

 genes, yet differentiation is what it attempts to explain. The 

 former theory also appears weak in the light of modern embryology. 



Lindsey has suggested that the action of genes is not limited 

 to the cells containing them, but that all genes of a kind in the 

 body, through the coordination which is evident in more obvious 

 phj^siological processes, act together to bring a character to expres- 

 sion. Some facts are apparently contradictory to this theory but 

 not necessarily inimical to it. 



A detailed discussion of these matters has no place in such a 

 work as this, especially since no theory is generally accepted and 

 none is more than a partial explanation. The facts given are 

 sufficient to illustrate our ignorance of the connection between 

 genes and the characters which they produce. So far we must 

 content ourselves with the knowledge that both exist and that 

 the appearance of characters is in accordance with definite laws 

 which are harmonious with the behaviour of the chromosomes and 

 the genes. 



Summary. Characters of organisms are determined by definite 

 things in the body, called factors. These factors are based upon 

 hypothetical bodies called genes, located in the chromosomes, and 



