DURATION IGl 



that the proportion of the cehular, parenchymatic, or fleshy elements 

 is so much greater than that of the woody that a woody character is not 

 apparent. In practical pharmacognosy, where dried roots are mostly 

 observed, a number of other terms for consistency, as in the case of the 

 bark, come into use. 



CLASSIFICATION OF STEMS 



Stems may be classified as to duration, order of development in time, 

 position, and nature of origin, mode of extension, direction of growth 

 and nature of support, modification of form or function, and consistence. 



Duration. — As to duration, they are, like roots, Annual, Biennial, and 

 Perennial. 



Herbs. — Annual stems are those which die at the close of the season. 

 They may or may not pertain to annual roots. Plants possessing them 

 are called Herbs. Herbs are therefore either Annual, Biennial, or Per- 

 ennial, in accordance with the character of the root, but their stems 

 are always annual. The definition of an herb is a plant, the aerial 

 portion of which dies at the season's close. The stem of an herb is 

 denominated Herbaceous. 



Biennial Stems. — Biennial stems are those which are produced, 

 usually underground like that of the potato (Fig. 440, b), during one 

 season, and perish after the production of their branches in the following 

 season. Occasionally, however, like the cabbage, a biennial stem is 

 aerial. 



Tubers. — Fleshy-thickened and biennial portions of underground 

 stems, such as the potato, are denominated Tul)ers (Fig. 440, a). Fig. 

 444 represents the vniderground portion of the Curcuma, and well 

 displays the difference between tubers and tubercles. 



Bulbs. — Basal biennial portions of stems which are invested by more 

 or less fleshy-thickened storage-leaves are called Bulbs. Bulbs will be 

 classified under the subject of buds. 



Perennial Stevis. — Perennial stems are those which live and extend 

 their growth from year to year. They are Determinate when their 

 growth of the season is self-limited and closes with the production of a 

 specially prepared Winter-bud, which protects the growing point for 

 continued growth the next season; Indeterminate, when no such bud 

 is formed, growth continuing until the apical portion is destroyed by 

 an inclement season. In the latter class we have the anomaly of a 

 perennial stem with an annual tip. 

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