TUBER. 73 



178. The BULB partakes of the nature of the bud. It consists 

 of an oval mass of short, thickened scales, closely compacted in 

 concentric circles and layers, emitting a stem from their midst 

 and roots from the base or collum (141). 



a. Bulbs are said to be tmiicated wben they consist of concentric layers, each 

 entire, and enclosing all within it, as in the Onion. But the more common 

 variety is the scaly bulb, consisting of tliickened concave scales, connected to- 

 gether at the base, as the lily, tulip. 



b. The bulb is renewed annually, at the approach of winter, by the develop- 

 ment of new bulbs in the axils of the scales, which increase at the expense of the 

 old. 



c. BulhUts are small, aerial bulbs, formed in the axils of the leaves upon the 

 stem, which, when matured, fall to the ground, take root, and produce a perfect 

 plant. The tiger-lily (Lilium bulbifenim) is an example, also several species of 

 the onion. Such plants are termed bulbiferous. 



FIG. 23. — Forms of the stem ; — 1, Allium ; 2, Arum; 3, Solanum tuberosum; 4, San- 

 guinaria ; 5, a spinous branch. 



179. The coRM is the dilated, subterranean base of a stem, 

 resembhng the bulb in form and position, but differing in struc- 

 ture, being composed of a uniform and sohd mass, without dis- 

 tinction of layers or scales. It has been improperly called a 

 solid bulb. Ex. Arum, or Lidian turnip. 



180. The TUBER is an annual, thickened portion of a subter- 

 ranean stem, provided with latent buds (called eyes), from 

 which new i)lants arise the succeeding year. It is the develop- 

 ment of buds" and the fact of its origin with the ascending axis, 

 that places the tuber among stems instead of roots. The pota- 

 toe is an example. 



