BOTANY 



PART I.— PLANT RELATIONS 



CHAPTER I. 



INTRODUCTION. 



1. General relations. — Plants form the natural covering 

 of the earth's surface. So generally is this true that a land 

 surface without plants seems remarkable. Xot only do 

 plants cover the land, but they abound in waters as well, 

 both fresh and salt waters. They are wonderfully varied in 

 size, ranging from huge trees to forms so minute that the 

 microscope must be used to discover them. They are also 

 exceedingly variable in form, as may be seen by comparing 

 trees, lilies, ferns, mosses, mushrooms, lichens, and the 

 green thready growths (algce) found in water. 



2. Plant associations. — One of the most noticeable facts 

 in reference to plants is that they do not form a monot- 

 onous covering for .the earth's surface, but that there are 

 forests in one place, thickets in another, meadows in 

 another, swamp growths in another, etc. In this way the 

 general appearance of vegetation is exceedingly varied, 

 and each appearance tells of certain conditions of living. 

 These groups of plants living together in similar conditions, 

 as trees and other plants in a forest, or grasses and other 

 plants in a meadow, are known as plant associations. These 



