CHAPTER XVII 



THE STRUCTURE AND CLASSIFICATION OF PLANT 



COMMUNITIES 



A ONE-CELLED plant, or individual of the first type as described 

 in the preceding chapter, has certain definite morphological parts 

 which are usually readily recognized and to which names are applied. 

 The cell wall, cytoplasm, nucleus, and nucleolus are such parts. 

 Likewise an oak tree, or individual of the second type, has easily 

 distinguishable morphological parts such as roots, stems, and leaves. 

 We may reasonably expect, therefore, to find somewhat comparable 

 structural parts in the case of an individual of the third type, the 

 plant community. This we shall be able to do, but, just as leaves, 

 stems or roots may be so reduced or so modified that they are very 

 difficult to recognize, so the structural parts of a plant community, 

 while very readily recognized in many cases, are often so reduced or 

 modified that their recognition is by no means easy. 



12L Technical Terms Applied to Plant Communities. —Plant 

 community is a non-technical term which may be applied to any 

 assemblage of plants growing together in a natural habitat. Such 

 terms as plant formation, plant association, consociation, society, 

 and colony are technical terms which should be used only after the 

 vegetation has been sufficiently studied so that its climatic and 

 successional relationships are reasonably well known. In order to 

 understand the structure and classification of plant communities 

 it is necessary to be familiar with the technical terms used in de- 

 scribing them and, therefore, these terms will be defined in the fol- 

 lowing paragraphs. 



It should be remembered that the kind of indi^'idual that we have 

 been calling a plant community is really a biome, or biotic commun- 

 ity. The animals are just as vitally important in its structural 

 make-up as are the plants. Since we are studying plant ecology, 

 however, and it is obviously- impossible to cover the field of animal 

 ecology at the same time, we will continue largely to disregard the 

 animal constituents of the communities. 



122. Plant Associations.— An individual, adult plant community 

 is called a plant association. A plant association, therefore, is an 

 individual of the third type, just as a plant is an individual of the 

 second type, and a cell an individual of the first type. 

 (192) 



