PLANT ASSOCIATIONS 275 



a forest association is dominated by the trees, and often by 

 one or two kinds of trees. This is so evident that most 

 people think of a forest as consisting of trees alone, when in 

 fact they are only part of a large population. In the same 

 way, a meadow is dominated by grasses, so that to many it 

 seems to be almost exclusively a grass population. Thus 

 each association is apt to have its dominating individuals 

 that characterize it. This fact has a very interesting cor- 

 ollary. The rest of the plant population must adjust itself 

 to the dominant individuals. .For example, in the forest 

 population, the other plants must adjust themselves to the 

 dominating trees. Very many of them are so constituted 

 that they can live in the shade of trees ; while others, like the 

 " spring flowers," by means of underground storage of food 

 in roots or stems, can spring up rapidly and come into flower 

 in the short period between the first warm days of spring and 

 the full foliage of the trees, thus finishing their work before 

 the shade becomes dense. 



Another notable feature of a plant community is that the 

 nearest relatives are the keenest competitors. If a certain 

 kind of plant has established itself in a community, it is 

 very difficult for a nearly related plant to obtain a foothold. 

 It must not be thought that the " competition " referred 

 to, whatever it may be, is of the active sort, but the word 

 at least figuratively describes a situation. This fact con- 

 tains some very practical suggestions. Our worst " weeds " 

 are not members of our native population, but immigrants. 

 In various ways, the native plants of foreign countries be- 

 come introduced into America. If they find near relatives 

 in our native population, they are not heard of as weeds ; 

 but if they find no near relatives, they are probably freer 

 from competition than they were in their native country, 

 and may become a pest. The important suggestion, how- 

 ever, is that the more kinds of plants there are on a given 

 area, the larger will be the total plant population. For 



