CHAPTER XLVI. 



VEGETATION IN RELATION TO ENVIRONMENT.* 



I. Factors Influencing Vegetation Types. 



900. All plants are subject to the influence of environment 

 from the time the seed begins to germinate until the seed is 

 formed again, or until the plant ceases to live. A suitable amount 

 of warmth and moisture is necessary that the seed may germi 

 nate. Moisture may be present, but if it is too cold, germination 

 will not take place. So in all the processes of life there are 

 several conditions of the environment, or the "outside" of plants, 

 which must be favorable for successful growth and reproduction. 

 Not only is this true, but the surroundings of plants to a large 

 extent determine the kind of plants which can grow in particular 

 localities. It is also evident that the reaction of environment 

 on plants has in a large measure caused them to take on certain 

 forms and structures which fit them better to exist under local 

 conditions. In other cases where plants have varied by muta- 

 tion (p. 338) some of the new forms may be more suited to the 

 conditions of environment than others and they are more apt 

 to survive. These conditions of environment acting on the 

 plant are 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 /actors, and the 

 study of plants in this relation is sometimes spoken of as ecology, f 



* For a fuller discussion of this subject by the author see Chapters XLVI- 

 LV1I of his "College Text-book of Botany" (Henry Holt & Co.). 

 f OIKO $ = house, and Xoyo 5 = discourse. 



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