xii CONTENTS 
CHAPTER IV 
BIOMETRY 
PAGB 
Biology and_ statistics—Normal variations—Definite 
differences — Biometrical methods—The normal 
curve—Probable error—The biometrical treatment 
of heredity—Correlation—Structural and mental 
characters—The law of ancestral heredity—The 
effect of selection—Johannsen’s theory of the pure 
line—Selection in pure lines and in populations - 80 
CHAPTER V 
THE THEORY OF MUTATION 
Objections to the theories of Lamarck and of Darwin— 
Aristotle and Dr. Thomas Brown on mutation— 
Galton and organic stability—Bateson and discon- 
tinuous variation—Symmetry—Merism—Similar and 
simultaneous variation—Homcosis—The views of 
de Vries — The effect of selection — Mutation 
in C£nothera — Eversporting varieties — Different 
methods of mutation—The survival of useless struc- 
tures - - - - - [21 
CHAPTER VI 
THE OLDER HYBRIDISTS 
K6élreuter — Knight — Herbert — Gaertner — Naudin — 
Millardet - - - - . - 159 
CHAPTER VII 
MENDELISM 
The double nature of animals and of the higher plants— 
Unit characters—The inheritance of definite char- 
acters in cross-bred maize—Mono-hybrids and di- 
hybrids—Mendel’s law—Gregor Johann Mendel— 
Experiments with peas—Dominance—Heterozygote 
forms—tThe case of the Andalusian fowl—The nature 
of allelomorphs - - - > - 194 
