9 8 



MAINE AGRICULTURAL EXPERIMENT STATION. 



I916. 



i. That the size of an individual bean was no absolute or 

 certain criterion whatever, as to the average size of its offspring. 

 He found that while some particular large beans always pro- 

 duced large offspring beans, other equally large ones always 

 produced small offspring beans. Some individual small beans 

 produced offspring of large average size, others produced beans 

 of small average size like the parent, and, in general, he showed 

 it to be quite impossible for anyone to tell merely from the size 

 of a bean itself whether its progeny will be large or small. 



The nature of Johannsen's results on this point have been 

 clearly set forth in the accompanying diagram. 



Average Size of 

 Seed on Plant grown 

 from above Seed 



Average Size of 

 Seed on plant grown 

 from a Seed of the 

 Above Plant 



Fig. 14. Diagram to illustrate Johannsen's results with beans. 

 (From Wood and Punnett). 



2. That a population of beans, no matter from how sup- 

 posedly "pure" a commercial variety it is taken, is really not a 

 homogeneous unitary aggregation, but instead is made up of a 

 varying number of lines or strains, each of which breeds true to 

 itself when propagated in isolation. In other words, the popu- 

 lation in question is a mixture of several component lines. The 

 individuals in each line produce offspring true to the type of 

 the line, rather than to the type of the population as a whole, 

 except in cases where by chance the population type and the 

 type of one or more lines happen to be the same. 



3. That when mass selection alters the population type it 

 does so by a process of isolating from the mixture certain strains 

 whose own types are different from the original general popula- 



