DOCTRINE OF EVOLUTION AND RELATED IDEAS 489 



influence evolution until they are represented in the protoplasm 

 of the germ cells (germ plasm) , so all the old qualities of the race, 

 both deep and superficial, in order to continue, must be repre- 

 sented in this germ plasm. When the germ cells have united, 

 inheritance has been determined. After this the parent may 

 influence the development of the new individuals, as the 

 mother mammal doubtless does while the young is carried in the 

 uterus or nourished by milk; but neither of these is a matter of 

 heredity in any sense. 



In those organisms in which there is no union, where a single 

 germ cell may develop into the adult, only one line of germ plasm 

 is involved and heredity seems a somewhat simpler thing. How- 

 ever, when two different strains of germ cells unite to start the 

 new generation, every cell of the new individual receives chromo- 

 somes, and probably other material, that came by way of both 

 ovum and sperm. It is believed that the hereditary qualities 

 are carried in some way by these chromosomes. Chromosomes 

 from the sperm, carrying definite characteristics of the father's 

 line, are closely mixed in the same nucleus with chromosomes 

 of the egg carrying characteristics of the mother's line. In 

 what way will these diverse complex chemical bodies influence 

 one another in the development of the body ? Will they blend 

 or will one swamp or exclude the other? If they blend, will 

 they add their tendencies; will they neutralize each other; or 

 will their union give rise to compounds so new as to carry 

 qualities that neither parent had ; or may all of these happen with 

 the different qualities? These are the questions of heredity. 

 Only recently have we begun to get real statistical and breeding 

 data that will help us to answer them. 



492. Mendel's Experiments. Gregor Mendel, an Austrian 

 monk, published in 1866 the results of breeding experiments 

 conducted by him, together with his interpretation of these. 

 His work was unknown until 1900. Since that time his facts 

 have been verified and enlarged, and his conclusions tested and 

 elaborated until we now include under " Mendelism " a large 

 body of exceedingly important facts and suggestive theories 

 and principles. 



