March, 1902.
CONTENTS.
| INTRODUCTION. | |
| The Problems of Heredity and their Solution, pp. [1]–39. | |
| Preliminary statement of Mendel’s principles, [8]. Relationof Mendel’s discovery to the law of AncestralHeredity, [19]. Heterozygote and Homozygote, [23]. Newconceptions necessitated by Mendel’s discovery, [26]. Simplealternative characters, or allelomorphs, [27]. Compoundallelomorphs and their components, [29]. Analytical Variations, [29].Relation of Mendel’s principle to continuousvariation, [32]. Dominance, [32]. Non-Mendelian phenomena, [33].False hybrids of Millardet, [34]. Brief historicalnotice, [36]. | |
| MENDEL’S EXPERIMENTS IN PLANT HYBRIDISATION, pp. [40]–95. | |
| Introductory Remarks, [40]. Selection of ExperimentalPlants, [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]. Numbersof each form in offspring, [52]. Second generation bred fromthe Hybrids, [55]. Subsequent generations bred from theHybrids, [57]. | |
| Offspring of Hybrids in which several differentiatingcharacters are associated, [59]. The reproductive cells ofthe 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-cellsand 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 inPeas, [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 andexceptional, [129]. Analysis of exceptions, [132]. The “mule”or heterozygote, [133]. | |
| IV. | Professor Weldon’s collection of “Other evidenceconcerning 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]. (3a) Buchsbaum case, [145].(3b) Telephone cases, [146]. (3c) Couturier cases, [147]. | |
| B. Seed-coats and Shapes. 1. Seed-coats, [148]. 2. Seed-shapes:(a) Rimpau’s cases, [150]. (b) Tschermak’s cases, [152].3. Other phenomena, especially regarding seed-shapes, inthe case of “grey” peas. Modern evidence, [153]. | |
| C. Evidence of Knight and Laxton, [158]. | |
| D. Miscellaneous cases in other plants and animals: | |
| 1. Stocks (Matthiola). Hoariness, [169]. Flower-colour, [170]. | |
| 2. Datura, [172]. | |
| 3. Colours of Rats and Mice, [173]. | |
| V. | Professor Weldon’s quotations from Laxton, [178]. |
| Illustration from Primula sinensis, [182]. | |
| VI. | The Argument built on exceptions, [183]. |
| Ancestry and Dominance, [185]. | |
| Ancestry and purity of germ-cells, [193]. | |
| The value of the appeal to Ancestry, [197]. | |
| VII. | The question of absolute purity of germ-cells, [201]. |
| Conclusion, [208]. | |
ERRATA.
p. [22], par. 3, line 2, for “falls” read “fall.”
p. [63], line 12, for “AabbC” read “AaBbc.”
p. [66], in heading, for “OF HYBRIDS” read “OF THE HYBRIDS.”
Note to p. [125]. None of the yellow seeds produced by Laxton’s Alpha germinated, though almost all the green seeds sown gave healthy plants. The same was found in the case of Express, another variety which bore some yellow seeds. In the case of Blue Peter, on the contrary, the yellow seeds have grown as well as the green ones. Few however were wholly yellow. Of nine yellow seeds produced by crossing green varieties together (p. [131]), six did not germinate, and three which did gave weak and very backward plants. Taken together, this evidence makes it scarcely doubtful that the yellow colour in these cases was pathological, and almost certainly due to exposure after ripening.
THE PROBLEMS OF HEREDITY AND THEIR SOLUTION[3].
An exact determination of the laws of heredity will probably work more change in man’s outlook on the world, and in his power over nature, than any other advance in natural knowledge that can be clearly foreseen.
There is no doubt whatever that these laws can be determined. In comparison with the labour that has been needed for other great discoveries we may even expect that the necessary effort will be small. It is rather remarkable that while in other branches of physiology such great progress has of late been made, our knowledge of the phenomena of heredity has increased but little; though that these phenomena constitute the basis of all evolutionary science and the very central problem of natural history is admitted by all. Nor is this due to the special difficulty of such inquiries so much as to general neglect of the subject.
It is in the hope of inducing others to follow these lines of investigation that I take the problems of heredity as the subject of this lecture to the Royal Horticultural Society.