Contents. v 
PAGE 
13. The Influence of External Conditions on Hereditary 
Values 485 
III. THE INCONSTANCY OF FASCIATED RACES 488 
14. The Inheritance of Fasciations 488 
15. Half Races with Heritable Fasciation 502 
16. Eversporting Varieties with Heritable Fasciation . . . 508 
17. The Significance of the Atavists 514 
IV. HERITABLE SPIRAL TORSIONS 527 
18. Spiral Disposition of the Leaves 527 
19. Rare Spiral Torsions 537 
20. Spirally Twisted Races 543 
21. The Significance of the Atavists 554 
PART III. 
THE RELATIONS OF THE MUTATION THEORY TO 
OTHER BRANCHES OF INQUIRY. 
I. THE CONCEPTION OF SPECIES ACCORDING TO THE THEORY 
OF MUTATION 567 
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 MUTATION. . 599 
6. The Significance of the Available Evidence 599 
7. The Explanation of Adaptations 606 
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. The Periodicity of Progressive Mutations 651 
13. Iterative Formation of Species 661 
14. The Biochronic Equation , 663 
INDEX 675 
