xii CONTENTS. 



PAGK 



Sect. 23. Torsion 859 



„ 24. The Twining of Climbing Plants 862 



„ 25. The Twining of Tendrils 865 



„ 26. Movements of growing Leaves and Floral Organs produced by Variations 



of Light and of Temperature 871 



CHAPTER V. 



Periodic Movements of the Mature Parts of Plants and Movements 

 dependent on Irritation. 



Sect. 27. Introduction 878 



„ 28. Review of the Phenomena connected with Periodically Motile and Irritable 



Parts of Plants 880 



„ 29. Mechanism of the Movements caused by Contact or Concussion . . 887 



„ 30. Mechanism of the Movements produced by Variations of Temperature 



and of Light 894 



„ 31. Mechanism of spontaneous periodic Movements 895 



CHAPTER VL 

 The Phenomena of Sexual Reproduction. 



Sect. 32. The Nature of Sexuality 896 



J, 33. Influence of the origin of the Reproductive Cells on the product of 



Fertilisation 904 



„ 34. Hybridisation 914 



CHAPTER VII. 



The Origin of Species. 



Sect. 35. Origin of Varieties 920 



„ 36. Accumulation of new characters in the Reproduction of Varieties . . 924 



„ 37. Causes of the Progressive Development of Varieties 928 



J, 38. Relationship of the Morphological Nature of the Organ to its adaptation to 



the Conditions of Plant-life 933 



„ 39. The Theory of Descent 940 



Appendix 94^ 



Index 963 



