EXPERIMENTAL STUDY OF HEREDITY 67 



characters it manifests, are the result of the combined 

 influence of inheritance and environment. A bean seed- 

 hngj[is green, not merely because it has inherited chloro- 

 plastids, but because it develops in sunKght; 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 succissive 

 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 reaHty 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 (C/. p. 40). 



