THE STBM, OE ASCENDING AXIS. 



39 



leaves and flowers to perish in autumn — a new bud to open tlie foUowing spring-^ 

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

 dicates, not the age of the plant, but tho destined age of each intemode. 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 pbemobsb root-stock, formerly described as a root, is a. 

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

 (prasraorsus). This is owing to the death of the earlier and lower iii- 

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

 pedata, benjamin-root (Trillium) are examples. 



186. Ceown OP THE ROOT designates a short stem with condensed 

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

 face soil after the leaves and annual stems have perished. 



IS?. 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 tho fact of its origin with the 

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

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



65 63 54 



TiibiTs as they grow. 54, Tho common potato (Salanum). 65, Artichoke (Helianthas) 

 66, 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 the air, 

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

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

 grope in tho dark, damp ground, cease at length to elongrito, swell up .it the ends 

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

 renewed growth the following year. 



