108 OEGANOGEAPHY. 



root. It is a slender branch which runs along beneath the sur- 

 face of the earth, emitting roots from its lower side, and buds 

 from its upper, in the same manner as the rhizome, and it is 

 considered by many botanists as a variety of that stem. The 

 only differences existing between the creeping stem as defined 

 above and the rhizome are its more slender form and entirely 

 subterranean course. The Sand Sedge or Carex (Carex arenaria) 

 {Jig. 210), and the Couch Grass {Triticum repens), afford good 

 examples of this stem. In some instances such stems serve im- 

 portant purposes in nature ; thus those of the Sand Sedge, 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, like those of the Couch Grass, are the 

 pest of the agriculturist, who finds it very difficult to destroy 

 them by cutting them into pieces, for as every node is capable 

 of developing a bud and roots, each piece into which they will 

 then be divided is capable of becoming an independent individual, 

 and therefore such an operation only serves the purpose of multi- 

 plying such stems by placing the separated parts under more 

 favourable circumstances for development. 



b. The Tuber. {Figs. 211 and 212.) — This is a subterranean 

 branch, arrested in its growth, and excessively enlarged by the 



Fig. 211. Tubers of the common Potato (Solanum tuberosum). 



deposition of starch and other nutritious substances in its tissue. 

 It has upon its surface a number of little buds, or eyes as they 

 are commonly called, from which new plants are ultimately 

 formed. The possession of these buds indicates its nature as 

 a kind of stem. The Potato {Jig. 211) and Jerusalem Arti- 



