A. INFLUENCE OF TEMPERATURE 238 _a._ High temperature _b._ Low temperature B. INFLUENCE OF MOISTURE 239 _a._ On vital functions _b._ On general development IV. ILLUMINATION OF LICHENS A. EFFECT OF LIGHT ON THE THALLUS 240 _a._ Sun lichens _b._ Colour-changes due to light _c._ Shade lichens _d._ Varying shade conditions B. EFFECT OF LIGHT ON REPRODUCTIVE ORGANS 244 _a._ Position and orientation of fruits with regard to light _b._ Influence of light on colour of fruits V. COLOUR OF LICHENS A. ORIGIN OF LICHEN-COLOURING 245 _a._ Colour given by the algal constituent _b._ Colour due to lichen-acids _c._ Colour due to amorphous substances _d._ Enumeration of amorphous pigments _e._ Colour due to infiltration CHAPTER VI BIONOMICS A. GROWTH AND DURATION OF LICHENS 252 B. SEASON OF FRUIT FORMATION 255 C. DISPERSAL AND INCREASE 256 _a._ Dispersal of crustaceous lichens _b._ Dispersal of foliose lichens _c._ Dispersal of fruticose lichens D. ERRATIC LICHENS 258 E. PARASITISM 260 _a._ General statement _b._ Antagonistic symbiosis _c._ Parasymbiosis _d._ Parasymbiosis of fungi _e._ Fungi parasitic on lichens _f._ Mycetozoa parasitic on lichens F. DISEASES OF LICHENS 268 _a._ Caused by parasitism _b._ Caused by crowding _c._ Caused by adverse conditions G. HARMFUL EFFECT OF LICHENS 269 H. GALL-FORMATION 270 CHAPTER VII PHYLOGENY I. GENERAL STATEMENT A. ORIGIN OF LICHENS 272 B. ALGAL ANCESTORS 273 C. FUNGAL ANCESTORS 273 _a._ Basidiolichens _b._ Ascolichens II. THE REPRODUCTIVE ORGANS A. THEORIES OF DESCENT IN ASCOLICHENS 273 B. RELATION OF LICHENS TO FUNGI 275 _a._ Pyrenocarpineae _b._ Coniocarpineae _c._ Graphidineae _d._ Cyclocarpineae III. THE THALLUS