Contents. V 



PAGE 



13. The IiWlMciice of External Conditions on Hereditary 



Values 4^5 



III. The Incgnstan'cy of Fasciated Races 4.S8 



14. The Inheritance of Fasciations 488 



15. Half Races with Heritable Fasciation 502 



16. Eversporting Varieties with Heritable Fasciation ... 508 



17. The Signitkance of the Atavists 514 



IV. IlERiTAnLE Spiral Torsions 5-^7 



18. Spiral Disposition of the Leaves 527 



19. Rare Spiral Torsions 537 



20. Spirally Twisted Races 54.^ 



21. The SignilicaiKe of the Atavists 554 



PART HI. 



THE RELATIONS OF THE MUTATION TiiEORV TO 



OTHER BRANCHES OF IXOriRY. 



I. The Conception of Species According to the Theory 



OF Mutation 5^7 



1. Systematic Biology and the Theory of Mutation 567 



2. Progressive, Retrogressive and Degressive Mutations. 569 



3. The Theoretical Distinction Between Species and Va- 



rieties 578 



4. The Practical Conception of Species 589 



5. The Parallel Between Systematic and Sexual Relation- 



ship 592 



II. The Range of Validity of the Doctrine of Mitation. . 599 



6. The Significance of the Available Evidence 599 



7. The Explanation of Adaptations (106 



8. Vegetative Mutations 614 



III. The Material Vehicles of the Hereditary Characters 631 



9. Darwin's Pangenesis 631 



10. Intracellular Pangenesis 639 



11. The Pangenes as Bearers of the Hereditary Char- 



acters 643 



IV. Geological Periods of Mutation 651 



12. I he Periodicity of Progressive Mutations 651 



13. Iterative I'ormation of Species 6()i 



14. The Biochronic Equation 663 



Index 675 



