EXPERIMENTAL STUDY OF HEREDITY 67 



characters it manifests, are the result of the combined 

 influence of inheritance and environment. A bean seed- 

 ling is green, not merely because it has inherited chloro- 

 plastids, but because it develops in sunlight; without 

 sunlight the green color could not come into expression. 

 If we vary any factor of environment (temperature, mois- 

 ture, illumination, food) the expression of the inheritance 

 may be altered, just as truly as though the inheritance 

 were changed. The characteristics expressed by any plant 

 (or animal] are the result of the combined action of inheri- 

 tance and environment. It is of fundamental concern to 

 a man, not only to be "well-born" (eugenics], but also 

 to be " well-placed " (euthenics), although the former, 

 according to present day conceptions appears to be more 

 important. 



58. Johannsen's Conception of Heredity. The con- 

 ception that inheritance, as previously noted, is not the 

 transmission of external characters from parent to off- 

 spring, but the reappearance, in successive generations, 

 of the same organization of the protoplasm with reference 

 to its character-units, was first developed by Johannsen, 

 of Copenhagen, Denmark, who proposed the term "genes." 

 "The sum total of all the 'genes' in a gamete or zygote," 

 is a genotype. Inheritance is the recurrence, in successive 

 generations, of the same genotypical constitution of the pro- 

 toplasm. Johannsen does not attempt to explain the 

 nature of the genes, "but that the notion 'gene' covers 

 a reality is evident from Mendelism." This conception 

 of heredity is diametrically opposed to the older and 

 popular conception, but is much more closely in accord 

 with the facts revealed by recent studies of plant and 

 animal breeding (Cf. p. 40). 



