TBE STEM 



59 



runnel's ; but these die in the following winter, if not before, and 

 leave tlie plants as so many separate individuals. 



91. Subterranean stems and branches. — These are very 

 imiuerous and various. The vegcetation that is carried, oii 



RUiziime of the Iris. 



4o. Rliizomes of the Pepx)erniint, 



underground is hardly less varied 

 or important than tliat above 

 ground. All their forms may be 

 referred to four principal kinds : 

 namely, the Rliizome, or Hootstoek, 

 the Tuber, the Conn or solid 1ju1)j, 

 and the true BnlJi. 



92. The rootstock, or rhizome, in its 

 simplest form, is merely a creeping stem 

 or brancli growing beneath tlie surface of the soil, or partly covered 

 by it (Fig. 45). 



93- liootstocks are commonly thickened by the storing up of con- 

 siderable nourishing matter in their tissue. The common species of 

 Iris (Fig. 46) in the gardens have stout rootstocks, which are only 

 partly covered by the soil, and which bear foli- 

 age leaves instead of mei'e scales, closely covering 

 the upper part, while the lower produces roots. 

 94. A tuber may be understood to be a por- 

 tion of a rootstock thickened, and with buds 

 (eyes) on the sides. Of course, there are all 

 gradations between a tuber 

 and a rootstock. Helkin- 

 thun ttiherosuf:, the so-called 

 Jerusalem Artichoke (Fig. 

 48), and the common 

 Potato, are typical and fa- 

 miliar ex- 

 amples of 

 the tuber. 



The stalks by which the tubers 

 in. Tubers of HeUaiUhus tuberosus. are attached to the parent stem 



47. Corm or Caudex, 

 of Trillium. 



