ORGANS OF NUTRITION. 



109 



choke {fig. 212) are good illustrations. A case was reported in 

 the ' Gardeners' Chronicle' of a Potato plant in which the buds 



Fig, 213. 



Fig. 214. 



Fig. 212. Tubers of the Jerusalem Artichoke {Helianthus hiberosus). 



Fig. 213. A monstrous branch or bud of the common Potato. From The 

 Gardeners' Chronicle. 



in the axils of the true leaves above ground showed a tendency 



/to form tubers {fig. 213), by which their analogy to steins was 



/ clearly indicated. The stem-like nature of the tuber is also cor- 



l roborated by the common experience of gardeners, who, by sur- 



/ rounding the lower part of the stems of the potato with earth, 



'' convert the buried buds (which under the usual circumstances 



would have produced ordinary branches) into tubers, and thus 



increase their number. 



c. The jB«/6.— This is a short- 

 ened, usually subterranean stem 

 or branch, generally in the form of 

 a rounded or flattened plate {fig. 

 214, a\ which bears on its sur- 

 face a number of fleshy scales or 

 modified leaves ; or it may be con- 

 sidered as a subterranean bud of a 

 scaly nature, which sends off roots 

 from below, and a stem upwards, 

 J), bearing leaves and flowers. 

 The scales are generally more or 

 less thickened by deposition of 

 nutritive matters ; these, there- 

 fore, serve as reservoirs of nutri- 

 ment for the future use of the 

 plant, just as in other cases the 

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

 in Monoeotyledonous Plants, as in the Lily {figs. 214, 215, and 

 216), Onion {fig. 217), and Tulip. The scales of a bulb, like 

 the ordinary leaves of a branch, have the power of developing 



Fig. 214. Verrical section of a bulb 

 of the Lil.v. a. Shortened axis or 

 plate, p. Flowering-stem. c. Late- 

 ral buds or cloves. 



