178 



BOTANY 



swollen. By the presence of scale leaves, with their axillary buds, 

 the absence of a root-cap and the internal structure, a rhizome or 

 tuber can be distinguished from a root. While all transitions between 

 rhizomes and shoot-tubers exist, roots are usually absent from the 

 latter, while the rhizomes, which may grow horizontally, obliquely, or 

 vertically, and be branched or unbranched, as a rule bear roots. 



In Fig. 138 is shown the root-stock of Solomon's Seal (Polygonatum multi- 

 florum), which has been already referred to as an example of a sympodium. At 



c, d, and e are seen the scars of the aerial shoots 

 of the three preceding years ; at b may be seen 

 the base of the stem growing at the time the 

 rhizome was taken from the ground, while at 

 a is shown the bud of the next year's aerial 

 growth. 



k 



FIG. 204. Longitudinal section 

 of Tulip bulb, Tulipa Gesneriana. 

 zk, Modified stem ; zs, scale leaves; 

 v, terminal bud ; Ic, rudiment of a 

 young bulb ; w, roots. (Nat. 

 size. After SCHENCK.) 



FIG. 205. Root- tubers of Dahlia variaUlis.' s, The 

 lower portions of the cut stems. (\ nat. size. 

 After SCHENCK,) 



The tubers of the Potato, of Colchicum autumnale, and Crocus sativus, are 

 examples of stem-tubers. The tubers of the Potato (Fig. 203) or of the Jerusalem 

 Artichoke (Helianthus tuterosus) are subterranean shoots with swollen axes and 

 reduced leaves. They are formed from the ends of branched underground shoots 

 or runners (STOLONS), and thus develop at a little distance from the parent plant. 

 The so-called eyes on the outside of a potato, from which the next year's growth 

 arises, are in reality axillary buds, but the scales which represent their subtending 

 leaves can only be distinguished on very young tubers. The parent plant dies 

 after the formation of the tubers, and the reserve food stored in the tubers 

 nourishes the shoots which afterwards develop from the eyes. 



In the Meadow Saffron new tubers arise from axillary buds near the base of the 

 modified shoot, but in the Crocus from buds near the apex. In consequence of this, 



