TABLE OF CONTENTS xi 



SECOND SECTION. 

 RELATIONSHIPS OF SYMMETRY. 



PAGE 



I. INTRODUCTION . . 65-73 



Polar construction 65 



Radial, bilateral, and dorsiventral organs 66 



Relationship between symmetry and direction of organs ... 67 



Orthotropous and plagiotropous organs 67 



Alternation of Orthotropous and plagiotropous growth ... 68 



Dorsiventrality and plagiotropous growth 70 



Radial construction and Orthotropous growth 70 



Illustrations from lichens 71 



II. POSITION OF ORGANS ON RADIAL AXES 73-84 



Sketch of the mechanical hypothesis of leaf-position. By Dr. Arthur 



Weisse 74-84 



III. DORSIVENTRAL SHOOTS 84-114 



1. Different structure of the upper and under side .... 84 



Epinasty and hyponasty 85 



2. Relationships of position 85-99 



Their connexion with the conditions of life 86 



A. Creeping and climbing shoots 90-92 



Flattening of their axes 92 



B. Dorsiventral lateral shoots 92-99 



Brought about by 



1. Change of position of leaves ...... 92 



a. In the development 92 



(a) By change of the leaf-insertion .... 93 



(b) By torsion of the internode or the leaf-base . 93 



(c) From the beginning at the vegetative point . 94 



b. Hereditary ......... 95 



2. Anisophylly 99 



C. Anisophylly 99-114 



Has varying degrees 99 



Historical sketch 99 



A. In Musci loo 



B. In Hepaticae 101 



C. In Pteridophyta 102-107 



Lycopodium 102 



Selaginella ......... 105 



D. In Spermaphyta 107-113 



a. Lateral anisophylly 108 



b. Habitual anisophylly 109 



1. In Urticaceae 109 



2. In Melastomaceae Ill 



3. In Acanthaceae . . . . . . . 112 



4. In Gesneriaceae 113 



Conclusions regarding anisophylly 113 



