Genotype and Phenotype 179 



generations of breeding for the smallest seeds to give rise 

 to offspring with small seeds, or for the large seeds to yield 

 offspring with consistently large seeds. This would indicate 

 that the systematic selection of seeds in this manner does 

 not bring about a distinct variety of a consistently diverg- 

 ing type. 



In another series of experiment, however, Johannsen 

 took from a mixed lot of seeds, which to all outward ap- 

 pearances might have been a sample from one variety, and 

 produced by means of pure line breeding some nineteen dis- 

 tinct types. In these experiments the character upon which 

 attention was fixed was the weight of the seed. A type was 

 considered established by a consistent fluctuation of seed 

 weights around a distinct mode (see Fig. 89). That is to 

 say, it was impossible from mere inspection to tell whether 

 a given seed belonged to one or another of these pure line 

 types. It was possible, however, by planting and raising a new 

 crop and then measuring the seeds, to show that each line pre- 

 served consistently its own range of variation in seed size. 



Genotype and Phenotype 



As a result of these experiments, Johannsen suggested 

 the importance of distinguishing between a type which is 

 such in appearance only and may include individuals of varied 

 hereditary capacity, and a type which is fairly uniform from 

 the hereditary point of view. To the former he gave the 

 name phenotype; and to the latter the name genotype. In 

 a mixed population there will be many distinct strains so 

 far as hereditary capacity is concerned but appearing to 

 casual inspection quite indistinguishable. For example, we 

 may find two men of the same stature, one of whom is a 

 short representative of a rather tall stock, whereas the other 

 is a tall representative of a short stock. Without knowing 

 anything of their families we should class them as having 

 the same character or quality — that is the same phenotype, 

 say a stature of 68 inches. From a knowledge of their an- 

 cestry or their offspring we might recognize them as belong- 



