THE PLANT COMMUNITY AN ORGANISM 



181 



these is the single cell. This was the first kind of individual that 

 appeared on earth and at first, of course, there was only the one type. 

 The single cell performed all of the functions that it is necessary for a 

 plant to i)erform and, of course, there was no such thing as division 

 of labor. After a while, however, some of these one-celled organisms 

 began to cling together and so form little colonies or communities 

 of cells. They were still all alike, each one performing all functions, 

 but from these little colonies have evolved the much larger com- 

 munities of cells that we call the higher plants and animals. Thus a 



Fig. 80.— a plant community consisting of many individuals. 



higher plant, such as a spruce tree (Fig. 81), is a community of mil- 

 lions of individuals of the first type of which we have spoken. It is 

 a representative of the second type of individual. In this individual, 

 which is really a community of cells, there is a decided division of 

 labor and a differentiation of form and structure among the com- 

 ponent individuals. 



Just as the second type of individual is a community composed of 

 individuals of the first type, so a plant community, which we con- 

 sider as the third type of individual, is composed of individuals of the 

 second type, largely, though some of the component individuals may 

 be of the first type. It is a little difficult at first to think of a ])lant 

 community as an individual in the sense that a tree is an individual, 

 because we have not been in the habit of so considering it, but there 



