52 PLANT BIOLOGY 



trees are always deliquescent, morning-glories are always 

 trailing or climbing, strawberries are always creeping. 

 We do not know why each plant has its own habit, but 

 the habit is in some way associated with the plant's gene- 

 alogy or with tJie way in which it has been obliged to live. 



The stem may be simple or branched. A simple stem 

 usually grows from the terminal bud, and side branches 

 either do not start, or, if they start, they soon perish. 

 Mulleins (Fig. 53) are usually simple. So are palms. 



Branched stems may be of very different habit and shape. 

 Some stem systems are narrow and erect ; these are said 

 to be strict (Fig. 54). Others are diffuse, open, branchy, 

 twiggy. 



Nodes and Internodes. The parts of the stem at which 

 buds grow are called nodes or joints and the spaces be- 

 tween the buds are internodes. The stem at nodes is 

 usually enlarged, and the pith is usually interrupted. The 

 distance between the nodes is influenced by the vigor of 

 the plant : how ? 



FIG. 59. RHIZOME OR ROOTSTOCK. 



Stems vs. Roots. Roots sometimes grow above ground 

 (Chap. VII); so, also, stems sometimes grow underground, 

 and they are then known as subterranean stems, rhizomes, 

 or rootstocks (Fig. 59). 



Stems normally bear leaves and buds, and thereby are 

 they distinguished from roots; usually, also, they contain 

 a pith. The leaves, however, may be reduced to mere 

 scales, and the buds beneath them may be scarcely visible. 



