CONTENTS. Xlll 



CHAPTER XIV. 



IRRITABILITY. 



Influence of the earth on the direction of growth, ig7. Influ- 

 ence of light on growth, 199. Influence of light on the di- 

 rection of growth, 200. Diaheliotropism, 201. Epinasty 

 and hyponastv, 202. Leaves with a fixed diurnal position, 

 203. Importance of these movements, 204. Influence of 

 light on the structure of the leaf, 205. Movement influ- 

 enced by contact, 206. Sensitive plants, 207. Movement in 

 response to stimuli, 208. Transmission of the stimulus, 209. 

 Cause of the movement, 210. Paraheliotropism of the 

 leaves of the sensitive plant, 211. Sensitiveness of insec- 

 tivorous plants, 212. Hydrotropism, 213. Temperature, 

 214 page 82 



PART II. 



MORPHOLOGY. 



CHAPTER XV. 



SPIROGYRA. 



Form of spirogyra, 220. Multiplication of the threads, 221. 

 How some of the threads break, 222. Conjugation of spiro- 

 gyra, 223. How the threads conjugate or join, 225. How 

 the protoplasm moves from one cell to another, 226. The 

 zygospores, 227. Life cycle, 228. Fertilization, 229. Sim- 

 plicity of the process, 230. Position of the plant spirogyra, 

 231 page 93 



CHAPTER XVI. 



CEDOGONIUM. 



Form of cedogonium, 235. Fruiting stage of cedogonium, 236. 

 Sexual organs of cedogonium; oogonium and egg, 237. 

 Dwarf male plants, 238. Antheridium, 239. Zoospore 

 stage of cedogonium, 240. Asexual reproduction, 241. Sex- 

 ual reproduction, 242. Antheridia, 242. Oogonia, 243. 

 CEdogonium compared with spirogyra, 244. Position of 

 cedogonium, 245. Relatives of cedogonium, 246 page 99 



