EXPERIMENTAL STUDY OF HEREDITY 561 
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 constitu- 
tion of the protoplasm. 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. 1 
484. Value of Mendel's Discoveries. The discoveries 
that, in inheritance, certain characters are dominant 
over certain others; that a given inheritance (e.g., condi- 
tions associated with seed-color, odor, eye-color, stature, 
musical ability, insanity, tendency to some disease) may 
be carried and transmitted to offspring by an adult 
who gives no outward signs of carrying the inheritance; 
that, under certain conditions of breeding, some characters 
(the recessive ones), whether good or bad, may become 
permanently lost; that dominant characteristics are 
certain to appear in some of the offspring all of these 
truths, learned by the study of a common garden vegetable, 
will be recognized at once as of enormous importance to 
the breeders of plants and animals, and above all to man- 
kind, in connection with our own heredity. They point 
the way to the explanation of such enigmas as the pro- 
verbial bad sons of pious preachers, spendthrift children 
1 A discussion of Johannsen's very fruitful method of "pure line" 
breeding belongs to more advanced studies. 
36 
