48 



MANUAL OF BOTANY 



differences existing between the creeping stem as defined above 

 and the rhizome are its more slender form, its commonly greater 

 length, and its entirely subterranean course. The Sand Sedge 

 {Carcx arenaria) {fig. 67), and the Couch Grass [Triticum 

 repens), afford good examples of this stem. In some instances 

 such stems serve useful purposes in nature ; thus those of the 

 Sand Sedge or Carex, by spreading through the sand of the sea- 

 shore, and in this way binding it together, prevent it from 

 being washed away by the receding waves. Others, on the other 

 hand, like those of the Couch "Grass, are the pest of the agri- 

 culturist, who finds it very difficult to destroy such stems by 



Fig 



Fig. 74. 



Fig. 73. Tunicated bulb of the Onion. Fiij. 74, Stem of a species of Lily 



(ZiUiim bulbifertim) bearing bulbils or bulblets, a, a, in the axils of its 

 leaves. 



cutting them into pieces, for as every node is capable of develop- 

 ing a leaf-bud and roots, each of the pieces into which they will 

 then be divided may become an independent individual ; and 

 therefore such a process, instead of destroying the plants, only 

 serves the purpose of still further multiplying them by jDlaeing 

 the separated parts under more favourable circumstances for 

 development. 



b. The Tuber (figs. 68 and 69).— This is a subterranean 

 stem or branch, arrested in its growth, and excessively enlarged 

 by the deposition of starch or other nutritious substances in its 

 tissue. It has upon its surface a variable number of little 

 buds, or eyes as they are sometimes called, from which new 

 plants are ultimately formed. The presence of these buds 



