THE STEM, OR ASCENDING AXIS. 



39 



leaves and flowers to perish in autumn a new bud to open the following spring 

 and a new internode with its roots to abide several years. The number of joints in- 

 dicates, not the age of the plant, but the destined age of each intdrnode. Thus if 

 there are three joints, we infer that they are triennial, perishing after the third sea- 

 son, while the plant still grows on. 



185. THE PREMORSE ROOT-STOCK, formerly described as a root, is a 

 short, erect rhizome, ending abruptly below as if bitten square off 

 (prcemorsus). This is owing to the death of the earlier and lower in- 

 ternodes in succession, as in the horizontal rhizome. Scabious, Viola 

 pedata, benjamin-root (Trillium) are examples. 



186. CROWN OF THE ROOT designates a short stem with condensed 

 internodes, remainiug upon some perennial roots, at or beneath the sur- 

 face soil after the leaves and annual stems have perished. 



187. THE TUBER is an annual thickened portion of a subterranean 

 stem or branch, provided with latent buds called eyes, from which new 

 plants ensue the succeeding year. It is the fact of its origin with the 

 ascending axis, and the production of buds that places the tuber among 

 stems instead of roots. The potato and artichoke are examples. 



56 5') 54 



Tubers as they grow. 54, The common potato (Salanum). 55, Artichoke (Helianthns) 

 56, Sweet potato (Convolvulus). 



188. How THE POTATO GROWS. The stem of the potato plant sends out roots 

 from its base, and branches above like other plants ; but we observe that its branches 

 have two distinct modes of development. Those branches which arise into t: 

 whether issuing from the above-ground or the under-ground portion of the stern, 

 expand regularly into leaves, &c , while those lower branches which continue to 

 grope in the dark, damp ground, cease at length to elongate, swell up at the ends 

 into tubers with developed buds and abundance of nutritious matter in reserve for 

 renewed growth the following year. 



