CHAPTER XVIII 



DESCRIPTIVE TERMS 



For the study of plants in the field the student will need cer- 

 tain descriptive terms which have not been given in the preceding 

 pages. In the following brief discussion, therefore, we shall define 

 the more important descriptive terms which the student will 

 need in studying the trees, shrubs, and herbaceous plants of the 

 spring flora. 



VEGETATIVE PARTS OF PLANTS 



Habitat. The term habitat is used to indicate the nature of the 

 environment in which individual plants or plant groups live. 

 The most common classification of habitats is that already 

 described, based upon the conditions of moisture, soil, and light 

 which constitute the environment. Habitats may therefore be 

 designated as metophytie, xerophytic, hydrophytic, and tropophytic, 

 according as the plants inhabiting these areas are mesophytes, 

 xerophytes, hydrophytes, or tropophytes in habit. 



Habit. The term habit includes the form and general appear- 

 ance of plants, based upon stem, branch, and leaf characters. 

 Thus, trees like the pines and spruces, with a main excurrent 

 trunk, are said to be erect in habit as compared with trees like 

 the elm, apple, and oak, in which the equal growth of several 

 branches produces a spreading habit. Plants are also said to be 

 caulescent when possessed of a definite aerial stem, to distinguish 

 them from plants like dandelions and strawberries, which are 

 designated as acaulescent, or without a visible aerial stem. 



Stems. Stems are either aerial, growing aboveground, or sub- 

 terranean, growing largely or wholly underground. The main 

 types of underground stems may be defined as follows : 



Rhizomes, like those of ferns or Solomon's seal (Fig. 207), are 

 horizontal underground stems furnished with buds and scalelike 



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