STEM 



27 



HERBACEOUS AND WOODY 

 STEMS. 



There is considerable variety 

 in the toughness, consistence, 

 and longevity of stems. A 

 stem may be soft and relatively 

 short-lived : in which case it is 

 said to be herbaceous. A 

 plant, the above-ground stems 

 of which are invariably her- 

 baceous, is described as a 

 herb. With the exception of 

 our herbaceous climbers {e.g. 

 Convolvulus) nearly all British 

 herbs are plants of low stature, 

 like the Buttercup and Prim- 

 rose. Opposed to herbs are 

 trees and shrubs whose stems 

 are hard and woody, and cap- 

 able of existing for consider- 

 able periods. A tree is dis- 

 tinguishable from a shrub by 

 its possession of a distinct 

 main-trunk which bears bran- 

 ches. A shrub is usually 

 smaller than a tree, and, in 

 place of having a main-trunk, 

 possesses several woody bran- 

 ches which spring from a 

 common point : e.g. Black- 

 berry. 



SECONDARY INCREASE IN 

 THICKNESS OF STEMS. 



The old part of the stem of 

 a grass, a palm, or almost any 

 Monocotyledon, is no thicker 

 than the young part near the 

 apex. The stem of the Mono- 



Fi^. 43.— Cymose branching of Chickweed (Stellaria media). The main stem (axis i.) 

 ends in a flower I., which is bent down in the figure. On the main stem there arise two 

 branches (axes 11.), each ending in a flower n. (which is bent down in the illustration), 

 and having two branches (axes iii.), which terminsfte in flowers in. ; and so on. 



