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, ctce., have distinct 
types of vegetation. The plants in ponds and hogs 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 cnvironmental factors. 
Throughout the preceding chapters Ecology has been touched 
upon repeatedly, for the adjustment of Icaves 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, Pteridophytes, 
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 
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