FOUNDERS OF PLANT BREEDING 
305 
This closes the account of the work in the field of hybridization 
from the time of Koelreuter to the time of Gregor Mendel, 1760- 
1866. Mendel’s investigations, however, did not become generally 
known until 1900, so that very little change occurred in the 
methods pursued in the study of hybrid phenomena until after 
the date last mentioned. Comparatively few students of plant 
breeding, however, realize the historical value of the work of the 
earlier hybridists, in whose experiments lie the germs of our 
present knowledge. 
Lamarck (1774-1829), the noted .French naturalist, taught that 
all living things have been derived from pre-existing forms, that 
the effects of use and disuse caused changes in bodily structure; 
that these changes were inherited and accentuated from genera- 
tion to generation. According to Lamarck, in plants and animals, 
whenever the conditions of habitat, exposure, climate, nutrition, 
mode of life, et cetera, are modified, the characters of size, shape, 
relations between parts, coloration, consistency are modified pro- 
portionately : some of the arguments against the validity of 
Lamarckism are : ( 1 ) that no one has ever been able to prove by 
experiment or otherwise, that the effects of use* the so-called 
“acquired characters” are inheritable, while innumerable facts 
indicate that they are not; (2) the hypothesis could apply only to 
the animal kingdom,, since plants in general have no nervous and 
muscular activities like those of animals. A hypothesis of organic 
evolution, to be valid, must apply equally to both plants and 
animals. 
The question of the method of evolution continued to be 
debated, with no satisfactory solution in sight, until 1859 when 
Charles Darwin published the greatest book of the nineteenth 
century, and one of the greatest in the world’s history, the “Origin 
of Species.” This book was the result of over twenty years of 
careful observations and thought. It consisted of the elaboration 
of two principal theories : ( 1 ) that evolution is the method of 
creation, (2) that natural selection is the method of evolution, 
based upon inheritance, variation, fitness for environment, strug- 
gle for existence, and survival of the fittest. 
The theory of heredity which was chiefly responsible for re- 
placing pangenesis was proposed by W eismann who was born at 
Frankfort on the Main in 1834 and died in 1914. In 1893, he 
published “The Germ-Plasm, A Theory of Heredity,” a treatise 
which elicited much discussion. The main features of Weis- 
mann’s Theory of Continuity of Germ plasm are as follows: 
