THEORY OF EVOLUTION 159 



On the contrary, some of the hnes would he 

 the same. 



The result means that the general population 

 is made up of definite kinds of individuals that 

 may have been sorted out. 



That his conclusion is correct is shown by 

 rearing a new generation from any plant or in- 

 deed from several plants of any one of these 

 lines. Each line repeats the same modal class. 

 There is no further breaking up into groups. 

 Within the line it does not matter at all whether 

 one chooses a big bean or a little one — thev will 

 give the same result. In a word, the germ 

 plasm in each of these lines is pure, or homo- 

 zygous, as we say. The differences that we find 

 between the weights (or sizes) of the individual 

 beans are due to external conditions to which 

 they have been subjected. 



In a word, Johannsen's work shows that the 

 fi'equency distribution of a pure line is due to 

 factors that are extrinsic to the germ plasm. 

 It does not matter then whicli individuals in a 

 pure line are used to breed from, for they all 

 carry the same germ plasm. 



We can now understand more clearly how 



