AERIAL STEMS. 



a growing point, and emitting roots from its base, and thus theoretically resembles the 

 leaf-bud of an aerial stem. It reproduces itself by developing buds, or cloves, at the 



base of its leaves or scales, 

 which buds grow at the ex- 

 pense of the parent plant, and 

 at length destroy it. There are 

 two kinds, according to the 

 arrangement of the leave? 

 First, the tunicated (Fig. 120), 

 when they more or less sur- 

 round the whole organ, and 

 cohere in a membranous sheet 

 of tissue. Such is the case 

 in the onion (alliutri). Secondly, 

 the naked, when the scales are 

 Fig. 122. The RUNNER, emitting roots and leaves at intervals, smaller and more fleshy, and 



are imbricated in rows one 



above another, as in the tulip. Both of these forms contain much starch (Fig. 121) 



and also many raphides (Fig. 87). 



They are not so exclusively com- 

 posed of cellular tissue as was 



noticed in the structure of the 



tuber ; but also contain vascular 



and woody structures. 



Aerial Stems are of five kinds, 



the Sucker, the Vine, the Eoot- 



stock, the Runner, the Offset, and 



the Pseudo-bulbs of orchidaceous 



plants. 



The Sucker is common in mo- 



nocotyledonous plants, as the 



pine-apple, and consists of a 



branch proceeding from the col- 



lum of a plant underground, 



which becomes erect and bears 



leaves, and subsequently emits 



roots from its base. In other 



instances it proceeds from the 



stem downwards to the earth, 



and there takes root. 



The Vine, as in the Vine (Vi- 



tis vinifera) and Cucumber 



(Cucumis), is a slender twining 



stem, which situates itself amongst 



and adheres to other plants for Fig. 123. The GINGER plant (Zingiber officinale), with 



support*,.. It does not give off lts rhlzome from whi CQ the leaves and flowers spring. 



foots along its course. 



The Runner^ on the other hand, is also a creeping stem ; but it emits a bundle of 



