SCOPE OF GENETICS 



all that it contains. I am aware that there is 

 interplay between the organism and the cir- 

 cumstances in which it grows up, and that 

 opportunity given may bring out a potenti- 

 ality which without that opportunity must 

 have lain dormant. But w hile noting paren- 

 thetically that this question of opportunity 

 has an importance, which some day it may be 

 convenient to estimate, the one certain fact is 

 that all the powers, physical and mental that 

 a living creature possesses were contributed 

 by one or by both of the two germ-cells which 

 united in fertilisation to give it existence. 

 The fact that tvjo cells are concerned in the 

 production of all the ordinary forms of life 

 was discovered a long while ago, and has 

 been part of the common stock of elementary 

 knowledge of all educated persons for about 

 half a century. The full consetpiences of this 

 double nature seem nevertheless to have 

 struck nobody before Mendel. Simple though 



