22 MENDELISM 



butterfly, or an apple-tree as each one thing. In order to 

 understand the significance of Mendelism we must get 

 thoroughly familiar with the fact that they are each two 

 things, double throughout every part of their constitution. 

 It is a good exercise tp examine the people one meets with 

 in daily life and to try, in a rough way, to analyze them 

 into the two assemblages of characters which are united in 

 them. That we are assemblages or medleys of our parental 

 characteristics is obvious. We all know that a man may 

 possess some of his father's features, whilst in other respects 

 he resembles his mother. Now it is not generally seen 

 that in each feature he is double. Yet it is obvious that 

 the contribution of the male and female germ-cells may, 

 in respect of any of the ingredients, be either the same 

 or different. In any case in which the contributions made 

 by the two cells is the same, the resulting individual is pure- 

 bred for that ingredient ; and in all respects in which the 

 contribution from the two sides of the parentage is 

 dissimilar, the resulting individual is cross-bred." 



Thus every character of an individual (animal or plant) 

 has a double origin. 



What is the constitution of the germ-cells which any 

 individual produces? " If both parent germ-cells brought 

 a certain character in then all the daughter germ-cells will 

 have it" (Law i) ; "if neither brought it in, none of the 

 daughter cells have it" (Law 2) ; "if it came in from one 

 side and not from the other, then, on an average, in half 

 the immediate descendants it will be present, and in the 

 other half it will be absent" (Law 4; p. 17). 



It follows that when a germ-cell transmits a certain 

 quality, it transmits it as an undivided unit to another 

 germ-cell — it transmits it undiluted, so that the resulting 

 germ-cells either contain a full share of a certain quality, or 

 none of it. That is, the quality is present or it is absent. 



