CHAPTER XXI 



ECOLOGICAL CLASSIFICATION OF PLANTS 



Nature of Ecology 



It is common observation that certain kinds of plants live 

 only in certain places. Thus regions distinct in type, such as 

 ponds, bogs, shady ravines, dry hillsides, etc., have distinct 

 types of vegetation. The plants in ponds and bogs are ad- 

 justed to much water, in shady ravines to shade and moist 

 air, and on dry exposed hillsides the plants are adjusted to hot 

 sunshine and dry soil. Certain kinds of plants are therefore 

 adjusted to a certain environment which is known as their 

 habitat. In order to thrive, a plant must be able to compete 

 with other plants and endure the hardships which the environ- 

 ment imposes upon it. It must be adjusted to the range of 

 temperature, amount of light and moisture, conditions of the 

 soil, surrounding plants and animals, etc. Plant Ecology is 

 the science which treats of the adjustments and distribution 

 of plants in relation to the various environmental factors. 

 Throughout the preceding chapters Ecology has been touched 

 upon repeatedly, for the adjustment of leaves and stems to 

 light, the storage of food in tubers and seeds for the next gen- 

 eration, the adjustments of flowers to various kinds of pollina- 

 tion, the parasitic and saprophytic habits, the adjustments for 

 living in the water or air, etc., really belong to Ecology. In 

 the classification of plants phylogenetically, which is emphasized 

 in the previous chapters of Part II, the basis of classification is 

 kinship, but in classifying plants ecologically the basis is ad- 

 justment to environment, and plants varying widely in their 

 phylogenetic relationships occur together in the same ecological 

 class. For example, Thallophytes, Bryophytes, Pteridoph3rtes, 

 and Spermatophytes occur together in some ecological classes 

 of water plants. 



Many of the problems of Agriculture have to do with the 

 securing of strains or varieties of crop plants better adjusted 



600 



