TUBER. 



73 



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

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

 concentric circles and layers, emitting a stem from their midst, 

 and roots from the base or collum (111). 



a. Bulbs are said to be tunicated when they consist of concentric layers, each 

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

 variety is the scalij bulb, consisting of thickened 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. Bulblets 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 bulbiferum) is an example, also several species of 

 the onion. Such plants are termed bulbiferous. 



FIG. 23. — Forms of the stem ; — l, Allium; 2, Arum; 3, Solanum tuberosu 

 guinaria ; 5, a spinous branch. 



m; 4, San- 



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

 resembling 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 Indian turnip. 



ISO. The TUBER is an annual, tliickened portion of a subter- 

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

 which new plants 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. 



