CHAPTER XXXIX. 



RELATION OF PLANTS TO ENVIRONMENT 

 OR ECOLOGY.* 



613. Influence of environment on the life processes of 

 plants. By environment is meant all those conditions or factors 

 outside of the plant which in any way influence its growth, form, 

 nutrition, reproduction, distribution, etc. The relation which 

 some of these conditions, or factors, bear to the plant has been 

 quite fully studied in some of the former chapters. For example 

 in Chapter XX it has been shown how the pollination of plants 

 is largely (in most cases wholly) dependent upon factors or 

 agencies outside of the plant, as in cross pollination by the wind 

 and insects. 



I. FACTORS INFLUENCING VEGETATIVE TYPES. 



614. These conditions of environment acting on the plants 

 a.re factors which have an important determining influence on the 

 existence, habitat, habit, and form of the plant. These factors 

 are sometimes spoken of as ecological factors, and the study of 

 plants in this relation is sometimes spoken of as ecology,^ which 

 means a study of plants in their home or a study of the household 

 relations of plants. These factors are of three sorts : first, physical 

 factors; second, climatic factors; third, biotic, or life, factors. 



*To THE TEACHER. Chapters XXXIX-XLI are intended to out- 

 line the subject of the relation of plants to environment, or ecology, and to 

 serve as the basis for informal talks at the discretion of the teacher, or parts 

 may be assigned for reading in connection with some of the studies in the 

 earlier chapters in the book. When possible, excursions should be arranged 

 to the fields or parks where many of the principles discussed in these chapters 

 can be illustrated. Talks by the teacher, illustrated by lantern views, can 

 also be given. 



f OIKOJ = house, and \6yos = discourse. 



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