viii CONTENTS 



CHAPTER PAGE 



VIII. Roots 135 



General features of roots 135 



Root structure 143 



Factors influencing the direction of growth in roots .... 150 



The soil as the home of roots 152 



Water, air, and parasitic roots 1G2 



Propagation by roots 163 



IX. Stems 166 



Characteristic featiu-es and types of stems 166 



General structure of stems 166 



Structure of monocotyledonous stems 187 



Structure of herbaceous dicotyledonous stems 192 



Structure of woody stems 197 



X. Buds: Growth of Stems; Pruning; Propagation by Stems 204 



Buds 204 



Growth of stems 213 



Pruning 221 



Propagation by means of stems 225 



XI. Leaves 233 



Characteristic features of leaves 233 



Primary and secondary leaves 234 



General structure of leaves 242 



Cellular structure of leaves 246 



The manufacture of food by leaves 252 



Factors influencing photosynthesis 257 



Transpiration from plants 260 



Respiration 269 



Special forms of leaves 270 



Uses of the photosynthetic food 273 



PART II 



Plants as to Kinds, Relationships, Evolution, and Heredity 



XII. Introduction 289 



XIII. Thallophytes 296 



Algae (Thallophytes with a food-making pigment) .... 296 



General characteristics 296 



Blue-green Algae (Cyanophyceae) 297 



Green Algae (Chlorophyceae) 301 



Brown Algae (Phaeophyceae) 318 



Red Algae (Rhodophyceae) 324 



Some Alga-hlce Thallophytes not definitely classified . . 329 



