24 



general population, ... in other words it will be mediocre." 

 Now, if the mean condition of the parental generation and of each 

 preceding generation in the same line deviates to the same 

 degree from the mean condition of the population, it becomes 

 an inevitable inference that in so far as hereditary influences are 

 concerned, the offspring must have the same mean character 

 regardless of the largeness or smallness of the individual seeds 

 from which those offspring have developed. 



This " fixity of type " which Johannsen finds in the " pure 

 line " was recognized by Galton in his treatment of pure breeds* 

 and it seems strange that he did not perceive that his sweet-peas 

 which he recognized and described as a self-fertilizing population 

 were at variance with this fixity of type in the pure breed. 

 Johannsen has brought harmony in Galton's results where there 

 was a previously unnoted discord, and has confirmed the laws of 

 "natural inheritance" and of "regression from mediocrity" as 

 applied to the characters of self-fertilizing populations. 



An important point which is brought out by these results of 

 Johannsen both from a scientific and an economic standpoint is 

 that the weight or size of an individual seed is not the hereditary 

 unit, but the character of all the seeds of each plant considered 

 as a whole. A plant which produces small seeds in general, 

 may produce some seeds which are larger than the smallest 

 seeds of another plant which produces large seeds in general, so 

 that when the student of heredity wishes to use seed-characters 

 or presumably any other repeated character, he must seek the 

 general condition of the character in question in each plant and 

 not depend upon the character of single seeds or single other 

 repeated organs. 



The economic application of this important principle is obvi- 

 ous. It has been very generally maintained by horticulturists 

 that varieties deteriorate as the result of the selection of small 

 seeds, tubers, etc., for propagation, but this proposition, while 

 satisfying a certain sense of logic, has rested on no scientific 

 research. The fixity of type in the "pure line " which now ap- 

 pears to be established, shows that no such deteriorating effect 



* Natural inheritance, 189. 



