THEORY OF THE PURE LINE 109 



Johannsen's experiments have so far only been pub- 

 lished in the form of a preliminary abstract, but his 

 conclusions are of such interest that it seems necessary 

 to draw attention to them. The proviso must be 

 made, however, that further evidence is necessary in 

 order to justify their complete acceptance. 



The experiments in question were made upon plants 

 which could be self -fertilized for a series of generations. 

 In this way many complications were avoided which 

 are inevitably introduced in the case of biparental 

 inheritance. Barley and kidney beans were among 

 the plants examined, and the simplest character con- 

 sidered was the size of the seeds of the latter as 

 measured by weighing. In this particular series of 

 experiments each plant was regarded as being 

 characterized by the average weight of the seeds 

 which it produced. 



All the descendants arising from a single plant by self- 

 fertilization are spoken of by Johannsen as making up 

 a ' pure line.' And the members of such a line showed, 

 in respect of the weight of their seeds, normal varia- 

 bility about a mean or type value. The general 

 population of bean plants, made up of a great number 

 of such pure lines, also exhibited a normal curve when 

 the weights of the seeds were plotted. The pure 

 lines composing such a population showed various 

 types, some of them close to the modal value of the 

 population, but others differing widely from it. If 

 now a somewhat widely deviating member of a par- 

 ticular line was selected for propagation, its off- 

 spring showed regression to the type of this par- 



