Mr Galton suggested that the new scientific firm should have a mathematician and a biologist as partners, and--soundest advice--a logician retained as consultant[2]. Biologist surely must one partner be, but it will never do to have him sleeping. In many well-regulated occupations there are persons known as “knockers-up,” whose thankless task it is to rouse others from their slumber, and tell them work-time is come round again. That part I am venturing to play this morning, and if I have knocked a trifle loud, it is because there is need. _March, 1902._ [2] _Biometrika_, I. Pt. I. p. 5. CONTENTS. INTRODUCTION. THE PROBLEMS OF HEREDITY AND THEIR SOLUTION, pp. 1–39. Preliminary statement of Mendel’s principles, 8. Relation of Mendel’s discovery to the law of Ancestral Heredity, 19. _Heterozygote_ and _Homozygote_, 23. New conceptions necessitated by Mendel’s discovery, 26. Simple alternative characters, or _allelomorphs_, 27. _Compound allelomorphs_ and their components, 29. Analytical Variations, 29. Relation of Mendel’s principle to continuous variation, 32. Dominance, 32. Non-Mendelian phenomena, 33. False hybrids of Millardet, 34. Brief historical notice, 36. MENDEL’S EXPERIMENTS IN PLANT HYBRIDISATION, pp. 40–95. Introductory Remarks, 40. Selection of Experimental Plants, 42. Division and Arrangement of Experiments, 44. Characters selected, 45. Number of first crosses, 47. Possible sources of error, 47. Forms of the Hybrids, 49. Dominant and recessive, 49. First generation bred from the Hybrids, 51. Numbers of each form in offspring, 52. Second generation bred from the Hybrids, 55. Subsequent generations bred from the Hybrids, 57. Offspring of Hybrids in which several differentiating characters are associated, 59. The reproductive cells of the Hybrids, 66. Statement of Mendel’s essential deductions, 67. Experiments to determine constitution of germ-cells, 68. Statement of purity of germ-cells, 72. Experiments with _Phaseolus_, 76. Compound characters, 80. Concluding Remarks, 84. MENDEL’S EXPERIMENTS WITH HIERACIUM, 96–103. A DEFENCE OF MENDEL’S PRINCIPLES OF HEREDITY, 104–208. _Introductory_, 104. I. The Mendelian Principle of Purity of Germ-cells and the Laws of Heredity based on Ancestry, 108. II. Mendel and the critic’s version of him. The Law of Dominance, 117. III. The facts in regard to Dominance of Characters in Peas, 119. The normal characters: colours of cotyledons and seed-coats, 120. Shape, 122. Stability and variability, 124. Results of crossing in regard to seed-characters: normal and exceptional, 129. Analysis of exceptions, 132. The “mule” or heterozygote, 133. IV. Professor Weldon’s collection of “Other evidence concerning Dominance in Peas.” A. In regard to cotyledon colour: Preliminary, 137. Xenia, 139. (1) Gärtner’s cases, 141. (2) Seton’s case, 143. (3) Tschermak’s exceptions, 145. (3_a_) _Buchsbaum_ case, 145. (3_b_) _Telephone_ cases, 146. (3_c_) _Couturier_ cases, 147.