THE STRUCTURE OF PLANTS. 5 



climbing or scandent. If is winds around other objects like the Bean 

 and Hop, it is voluble or twining. 



16. Branches which arise from the main stem, below the surface of 

 the earth, are called suckers. 



If a branch bends over so as to reach the ground and there takes root, 

 a stolon is formed, which sends up branches of its own, and by the di- 

 vision or the dying away of the connecting portion, becomes an inde- 

 pendent plant. Plants multiplying in this way are stoloniferous. A long 

 slender thread-like branch which strikes root at its extremity, as in the 

 strawberry, is called a runner. 



Spines or thorns are hardened sharp-pointed branches ; they may fre- 

 quently be found bearing leaves, especially in their young state, which 

 shows their true character. Sometimes the thorns are branched, as 

 those of the Honey Locust. 



A tendril is a weak, leafless branch, capable of coiling around objects 

 to support climbing plants (Fig. 95). Some tendrils, however, belong 

 to the leaf (26). 



17. Besides the aerial form of the stem and branches, there are sev- 

 eral subterranean ones which are often mistaken for roots, but are to be 

 distinguished from them by having nodes, producing regular buds, and 

 often having rudiments of leaves (11). The Root-stock or Rhizoma is an 

 under-ground stem, advancing by its terminal bud and throwing off 

 roots from each node or from the whole surface ; the Couch- or Quitch- 

 grass furnishes a good illustration of one form of rhizoma ; it often be- 

 comes fleshy, as in the Sweet Flag and Bloodroot. 



18. Where an underground stem thickens at the apex, a Tuber is 

 formed, as is the case in the Jerusalem Artichoke and Potato. Though 

 popularly considered as a root, the potato is a short thick under-ground 

 stem, having scars which are the rudiments or representatives of leaves, 

 and the " eyes " are buds in their axils. A Corm or solid bulb is a more 

 or less globular subterranean stem, as that of the Indian Turnip. A 

 bulb is a very much shortened stem, covered with scales, which are the 

 thickened bases of former leaves. The White Lily has the scales sepa- 

 rate, and affords an example of the Scaly bulb, while in the Onion the 

 scales surround one another and form a Tunicated or Coated bulb. The 

 stem is here often reduced to a mere plate, from the lower surface of 

 which proceed the roots, and from the upper the scales. Bulblets are 

 small bulbs produced above ground ; the Spotted Lily of the gardens 

 bears these in the axils of the leaves, and in the Wild Leek, or Garlic, 

 they appear in the place of flowers. 



19. The internal structure of the stem presents two marked varieties. 

 In dicotyledonous plants, the woody portion occupies a ring between the 

 pith and bark, and in stsms of this kind which last from year to year, 

 they increase by an annual deposition of wood outside of that of the 

 previous year ; such plants are termed Exogenous or Exogens, (meaning 

 outside growers). The stem of a mouocotyledonous plant presents no 

 such distinction into pith, wood and bark, but the wood is in threads or 

 fibres, distributed irregularly throughout the pith, as is seen in cutting 



