VI 1.] STEM. 71 



excepting when they form a flowering branch. The coi. 

 sequence is that their stems remain unbranched. 



We have already referred to the distinction between 

 woody and herbaceous stems. Besides erect or ascending 

 annual flowering-stems, many herbaceous plants possess a 

 stem which either creeps upon the surface of the ground, 

 or which spreads wholly under the surface, giving ofl" leafy 

 and flowering shoots above and roots below. This under- 

 ground form of creeping stem is called a rhizome. Beginners 

 are very liable to regard it as a root, and such is the 

 common notion respecting it. The capacity of developing 

 leaf-buds at regular intervals, and the presence of leaves in 

 the very reduced form of minute scales, indicate its true 

 stem character. In many plants, spreading underground 

 stem-branches become greatly thickened, like tuberous roots, 

 and serve the same end in the economy of the plant. We 

 have a good example in the Potato and Yam. The *' eyes " 

 of the Potato are leaf-buds, and shoots develope from them 

 when planted or placed in damp cellars. Such thickened 

 portions of underground stem are called tubers. Some- 

 what similar is the very short and abruptly- thickened base 

 of the erect stem of some herbaceous plants distinguished 

 under the name of corm. In the Onion, Lilies, and Crinum 

 we have an analogous condition, disguised by very nume- 

 rous, 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 portion is the 

 excessively shortened stem from which the tall flowering 

 peduncles arise. Stems of this kind, with the internodes 

 suppressed and covered by thickened, scaly leaves, are 

 called bulbs. They may be regarded as equally leaf and 

 stem formations. 



