40 



THE STEM, OR ASCENDING AXIS. 



189. The corm is an under-ground, solid, fleshy stem, witli con- 

 densed internodes, never extending, but remaining of a rounded form 

 covered with thin scales. It is distinguished from roots by its leaf-bud, 

 •which is either borne at the summit, as in the crocus, or at the side, as 

 in the colchicum and putty-root (Aplectrum). 



190. HoTV THE COEM GROWS. The corm usuully accomplishes its part in vegeta- 

 tion in one or two seasons, and then gradually yields up its substance and life for 

 the nourishment of the new progeny fonned from the axils of its upper scales in 

 case of the Crocus and Gladiolus, or the single new corm from the axil of a lateral 

 scale, as in Colchicum. 



5T, Corms of putty-root (Apleotiutn) ; a, of laat year, 6, of the j)rcscnt year. 58, Scale bulb of 

 white lily. 59, Scale bulb of Oxalis violacea. 



191. The Bulb partakes largely of the nature of the bud. It con- 

 sists of a short, dilated axis, bearing an oval mass of thick, fleshy scales 

 closely packed above, a circle of adventitious roots around its base, and 

 a flowering stem from the terminal, or a lateral bud. 



192. How MULTIPLIED. Bulbs are renewed or multiplied annually at the ap- 

 proach of winter by the development of bulbs from the axils of the scales, which 

 increase at the expense of the old, and ulti- 

 mately become detached. Bulbs which flow- 

 er from the terminal bud are necessarily either 

 annual or biennial : those flowering from an 

 axillary bud may be perennial, as the termi- 

 nal bud may in this case continue to develop 

 new scales indefinitely. 



193. Bulbs are said to be tunicated 

 when they consist of concentric layers, 

 each entire and enclosing all within- it, co. Bulb of Liiium superbnm, with haWt 



as in the onion. But the more com- "^ " rhizome ; a, fUll-grown bulb sending 

 . j^ . ., 7 17. . . "P n terminal stem c, and two offeets hb, for 



mon variety is tne scaly bulb — consist- the bulbs of next year. 



ing of fleshy, concave scales arranged spirally upon the axis, as in the 



lily. 



