SYMBIONTICISM IN RELATION TO HEREDITY 123 



necessarily imply that the chromatin of the nucleus has no 

 effect upon the differentiation of the three localized areas. 



The acquisition of a new sj-mbiont in the cells of an or- 

 ganism may be the means by which new genes are added to 

 the multitude of those already present in the germ cell. 

 It appears that the more logical and reasonable nature of 

 such a contribution Ues in the manner by which a transfer 

 of chromatin material takes place from the bacterial sym- 

 biont to the germplasm of the host. When such a transfer 

 is once made, the "new" genes enter into the mechanism 

 of heredity, and constitute new factors which enter into the 

 complex of hereditary variations. It is not beyond the 

 realm of possibiUty that such new genes not only control 

 their own hereditary characters, but they may modify other 

 characters as well. The possible accretions of chromatin 

 material in SjTiibionticism will be discussed more fully 

 in the next chapter. 



It is well known that mitochondria are prominent in the 

 tissues of the embyro. What role do these bacterial bodies 

 play in ontogenetic development? It has been observed 

 by a number of investigators that mitochondria increase 

 by simple fission. It has also been found that mitochondria 

 are more or less equally distributed to the daughter cells 

 in mitosis. As development proceeds the cells become 

 differentiated into speciahzed groups. What, we may ask, 

 are the factors concerned in this differentiation? In 

 another place, we have mentioned the influence of intrinsic 

 environment acting in conjunction with the hereditary 

 potentiahties of the cell. Under the caption of "The Im- 

 mediate Causes of Differentiation," Wilson ('25) has given 

 a brief account of the ideas that have been advanced on the 

 subject. He says: 



The purely speculative side of this question need not long 

 detain us. DeVries, in his remarkable work Intracellular Pan- 

 genesis (1889) considered differentiation to result from the ac- 



