60 THE LEAVES. [CHAP. 



shoots develop from them when planted or placed in damp 

 cellars. Such thickened portions of underground stem 

 are called tubers. Somewhat similar is the very short 

 and abruptly-thickened base of the erect stem of some 

 herbaceous plants, as Crocus and Arum, distinguished 

 under the name of corm. In the Onion and Hyacinth 

 we have an analogous condition, disguised by very numer- 

 ous, much-thickened, scale-like leaves. If we peel off 

 these scales successively, until they be all removed, we 

 find a flattened, or conical, solid base remains, from the 

 under side of which root-fibres are given off. This por- 

 tion is the excessively shortened stem, from which trie 

 tall flowering peduncles arise. Stems of this kind, with 

 the internodes suppressed and covered by thickened, 

 scaly leaves, are called bulbs. Bulbs may be regarded 

 as equally leaf and stem formations. 



Perennial herbs, the flowering and leafy stems of which 

 die down annually, often form a 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 with this form of perennial stock to those in 

 which more of the exposed portion of the stem is peren- 

 nial, as in bushes, shrubs, and trees, is quite gradual. 

 Compare, in this respect, Monkshood, Cranesbill, Butter- 

 cup, Carnation, Fuchsia, Bramble, and Lavender. 



The forms of stem and the direction which they assume 

 above ground are exceedingly varied. Most of the modi- 

 fications which they present are denoted by terms in 

 ordinary use. Thus the stem may be erect, procum- 

 bent, or prostrate ; cylindrical, angular, triangular, quad- 

 rangular, furrowed, and so on. 



Branches sometimes assume very anomalous forms, and 

 might be mistaken for distinct structures, as in the spines 

 of the Hawthorn, and the tendrils of the Grape-vine and 

 Virginian Creeper. All spines and tendrils, however, are 

 not arrested or specially modified branches ; they are 

 often leaves or leaf-appendages, as is the case with the 

 spines of the Barberry and the tendrils of the Pea. 



