94 



STRUCTURAL BOTANY. 



[79, 80. 



234. The growth of the rhizome is instructive, marking its peculiar character. 

 Each joint marks the growth of a year. In Spring, the terminal bud unfolds 

 into leaves and flowers, to perish in Autumn a new bud to open the follow- 

 ing Spring, and a new internode, with its roots, to abide several years. The 

 number of joints indicates, not the age of the plant, but the destined age of 

 each internode. Thus if there are three joints, we infer that they are trien- 

 nial, perishing after the third season, while the plant still grows on. 



235. THE PRJEMORSE ROOT, or ROOT-STOCK, is short, 

 erect, ending abruptly below, as if bitten square off 

 (praemorsus). This is mostly owing to the death of 

 the earlier and lower internodes in succession, as in 

 the horizontal rhizome. The root of Scabious and the 

 rhizomes of Viola pedata and Benjamin-root are ex- 

 amples. 



Tubers as they grow. 280, The common Potato (Solanum). 261, Artichoke (Helianthus). 262, Sweet 



Potato (Convolvulus). 



236. CROWN OF THE ROOT designates a short stem 

 with condensed internodes, remaining upon some per- 

 ennial roots, at or beneath the surface-soil, after the 

 leaves and annual stems have perished. 



237. THE TUBER is an annual thickened portion of 

 a subterranean stem or branch, provided with latent 



