72 LEAVES. \c\{\\'. 



Perennial herbs, the flowering and leafy stems of which die 

 down annually, often form a permanent tufted mass, called a 

 stock, either wholly or partially hidden under the surface of 

 the ground. The stock results from the persisting bases of 

 the leafy stems. From the axils of the scale-like leaves 

 which these persisting stem-bases bear the annual shoots 

 are thrown up each spring. The passage from plants Avith 

 this form of perennial stock to those in which more of the 

 exposed portion of the stem is perennial, as in bushes, 

 shrubs, and trees, is quite gradual. 



The form of stems and the direction which they assume 

 above ground are exceedingly varied. Most of the modifi- 

 cations which they present are denoted by terms in ordinary 

 use. Thus the stem may be erect, procumbent, or prostrate ; 

 cylindrical, angular, furrowed ; and so on. 



Branches sometimes assume very anomalous forms, and 

 might be mistaken for distinct structures, as in the spines 

 of some varieties of Orange and Lime, or the common 

 Flacourtia sepiaria, and in the tendrils of the Grape-vine 

 and many garden Trumpet-flowers {Bignonias). All spines 

 and tendrils, however, are not arrested or specially modified 

 branches ; they are often leaves or leaf-appendages. 



The internal structure of the stem may be more suitably 

 described when we speak of cells and tissues. 



4. Leaves. — We have already spoken of leaves as originat- 

 ing around the growing apex of the stem as minute, cellular 

 projections. They are never terminal organs ; neither are 

 they, normally, capable of forming buds upon their surface. 

 The arrangement of the foliage-leaves upon tlie stem, though 

 at first sight it may appear accidental, is according to a law 

 generally constant in the same kind of plant. Compare, 

 with respect to leaf-arrangement, a young shoot of Tamarind 

 H'ith one of the Oran^^e or Banyan. Try to find two leaves 



