310 
IOWA ACADEMY OF SCIENCE Vor,. XXIX, 1922 
the reappearance, in successive generations, of the same organi- i 
zation of the protoplasm with reference to its character-units, was 
first developed by Johannsen, of Copenhagen, Denmark, in 1909, < 
and published in his book “Elements der Exakten Erblichkeitslehre 
(Elements of the teaching of exact heredity). Johannsen pro- 
posed the term “genes.” The sum total of all the genes in a 
gamete or zygote is a genotype. Inheritance is the appearance, 
in successive generations, of the same genotypical constitution of 
the protoplasm. 
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. 
Department oe Botany 
Iowa State College. 
BIBLIOGRAPHY 
Babcock, E. B., and Clausen, R. E., Genetics in Relation to Agriculture, 
1918. 
Bateson, W., Mendel’s Principles of Heredity, 1909. 
Castle, W. E., Genetics and Eugenics, 1916. 
Coulter, John M. and M. C., Plant Genetics, 1919. 
East, Ed. M., The Relation of Certain Biological Principles to Plant Breed- 
ing: Conn. Ag. Exp. Station Bull., 158, 1-93; 1907. 
Gager, C. Stuart, Heredity and Evolution in Plants, 1920. 
Fundamentals of Botany, 1916. 
Green, J. Reynolds, A History of Botany (1860-1900), 1909. 
Hayes, H. K., and Garber, R. G., Breeding of Crop Plants, 1921. 
Johannsen, W., Elemente der Exakten Erblichkeitslehre, 1913. 
Locy, Wm. R., Biology and its Makers, 1908. 
Eotsy, J. P., Vorlesungen uber Deszendenz theorien, 1906. 
Pummett, R. C., Mendelism, 1915. 
Roberts, H. F., The contribution of Carl Friedrich von Gartner to the 
Theory of Plant Hybridization: Am. Naturalist 53, 451-455; 1919. 
Darwin’s Contribution to the Knowledge of Hybridization : Am. 
Naturalist 53, 538-554; 1919. 
The Founders of the Art of Breeding: The Journal of Heredity, 
10, 99-106, 147-152, 229-239, 257-270; 1919. 
Sachs, J. von, History of Botany (1530-1860), 1906. 
Scott, Wm. B., The Theory of Evolution, 1917. 
Vries, Hugo De, The Mutation Theory, 1909. 
* Plant Breeding, 1907. 
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