CHAPTER XXVI 



ECOLOGICAL GROUPS; REGIONAL DISTRIBUTION OF PLANTS 1 



439. Ecology in earlier chapters. The term ecology has 

 already been denned (Sect. 110). In the preceding chapters 

 of this book the ecology of the plant has usually been some- 

 what discussed along 

 with the account of the 

 plant itself and of its or- 

 gans. For instance, much 

 of what was said about 

 the relations of the root 

 to the soil (Chapter 

 III), root-tubercle bac- 

 teria (Chapters III and 

 XXIV), mycorrhiza 

 (Sect. 38), and the rela- 

 tions of stem and leaf 

 to light supply (Chapter 



FIG. 357. The duckweed, one of the simplest 

 floating seed plants 



IV) is a part of plant 

 ecology. So, too, is the 

 treatment of pollination 

 (Chapter VIII), of seed dispersal (Chapter IX), and much 

 of the chapter on Weeds. The relation of parasites to their 

 hosts and of symbionts to each other (Chapter XXI) consti- 

 tutes a most important part of ecological botany. In the cases 

 here referred to, however, the main emphasis was laid on the 



1 See Warming, (Ecology of Plants (Clarendon Press, Oxford) ; Schimper, 

 Plant Geography on a Physiological Basis (Clarendon Press, Oxford) ; and 

 Coulter, Barnes, and Cowles, Textbook of Botany, Part II (American Book 

 Company, New York). 



An excellent bibliography of the subject will be found in Warming's work. 



477 



