16 



OKGANOGRAPHY. 



their analogy to stems was clearly indicated ; this is also cor- 

 roborated by the common, experience of gardeners, who, by 

 surrounding the lower part of the stems of tlie potato with 

 earth, increase the number of tubers by converting the buried 

 buds (which under the usual circumstances would have pro- 

 duced ordinary branches) into those organs. 



F'kj. 222. 



c. The Bulb. — This is a short- 

 ened, usually subterranean stem 

 or branch, generally in the form of 

 a rounded or flattened plate {fig. 

 222), which bears on its surface 

 a number of fleshy scales or 

 modified leaves; or it may be con- 

 sidered as a subten-anean bud of 

 a scaly nature, which sends off 

 roots from bcloAV, and from its 

 centre upwards a stem with 

 foliage and flowers. The scales 

 are generally more or less 

 thickened by deposition of nutri- 

 tive matters ; these, therefore, 

 serve as reservoirs of nutriment 

 for the future use of the plant, just as in other cases the en- 

 larged stems serve a similar purpose. The bulb is only found 

 in Monocotyledonous Plants, as in the Lily {figs. 222, 223, 

 and 224), Onion {fig. 225), Tulip, &c. The scales of a bulb, 



Fig. 222. Bulb of Lily. a. Shortened 

 axis or plate, p. Floweriiig-stem. 

 c. Lateral buds or cloves. 



Figs. 223 and 224. Scoly bulbs of the Lily. 

 (/, J. Flowering stem. 



Shortened axis. 6, h. Roots. 

 . Scales. 



like the ordiunry leaves of a branch, have the ]i()wer of develop- 

 ing in their axils new l)ull)s {fig. 222, c), called by gardeners 

 cloves, which circumstance is an additional proof of the analogy 

 of a bulb to a branch or l)ud. There are two kinds of bulbs com- 

 monly distinguished by botanists, namely the tunicated{fiy. 225), 

 and the scaly {fig. 224). The tunicated bulb is well scon in the 



