62 STUDY OF COMMON PLANTS. 



RBVIBVST AND SUMMARY. 



The stems of plants exhibit certain inherited pecu- 

 liarities of form, structure, and habit. In some large 

 families, the mints, for example, the stem is 

 struotme, Square ; while in others, as the true sedges, it 

 and habit. jg triangular. The cylindrical form, however, 

 which has important mechanical advantages in its favor, 

 is most common. Characteristic habits, manifested in 

 mode of growth or choice of surroundings, are also fre- 

 quently met with. Thus, the family to which the morn- 

 ing-glory belongs is particularly distinguished by its 

 climbing habit, the members of the water-lily family by 

 their aquatic habits, and so on. Structural peculiarities 

 are still more distinctive and far-reaching; so that, as a 

 rule, we readily determine the class to which a plant 

 belongs by ascertaining the arrangement of the tissues 

 composing the stem. 



The texture of the stem, as determined by the nature 

 of its elements, is often characteristic. Various families 

 Tertnreand °^ plants, as those to which the maple, oak, 

 duration. and wiUow belong, have woody stems ; while 

 others, as the pink and violet families and many others, 

 are herbaceous. The duration of the plant corresponds 

 rather closely to the nature of the stem. Woody plants 

 are perennial, living for an indefinite period, while herba- 

 ceous ones are commonly annual or biennial. These dis- 

 tinctions, however, are not to be pressed too far, since the 

 texture of the stem is subject to much variation, even in 

 the same species, and duration is greatly influenced by 

 climatic conditions. 



While typical stems are distinguished by the various 

 characters already referred to, there are many others that 



