LESSON 6.] SUBTEEEANEAN FORMS : TUBEES. 



43 



TrilliXiin or Birthroot (Fig. 67) life is reduced to a very narrow 

 span, only an' inch or less intervening between death beneath and 

 young life in the strong bud annually renewed at the summit. 



103. A Tuber is a thickened portion of a rootstock. "When slender 

 subterranean branches, like those of the Quick-grass or Mint (Fig. 

 64), become enlarged at the growing end by the accumulation there 

 of an abundance of soUd nourishing matter, tubers are produced, like 

 those of the Nut-grass of the Southern States (which accordingly be- 

 comes a greater pest even than the Quick-grass), and of the Jerusalem 

 Artichoke, and the Potato. The whole formation may be seen at a 

 glance in Figure 68, which represents the subterranean growth of a 

 Potato-plant, and shows the tubers in all their stages, from shoots 

 just beginning to enlarge at the tip, up to fiilly-formed potatoes. 

 And Fig. 69, — one of the forming tubers moderately magnified, — 

 plainly shows the leaves of this thickening shoot, in the form of little 

 scales. It is under these scales that the eyes appear (Fig. 70) ; 

 and these are evidently axillary buds (43). 



104. Let us glance for a moment at the economy or mode of life 

 of the Potato-plant, and similar vegetables, as shown in the mor- 



FIG, 68. Forming bibers of the Potato. 69. One of the very young potatoes, moderately 

 magnified. 70. Slice of a portion through an eye, more magnified. 



