UNDERGROUND STEMS 



135 



It is this abundant store of food that makes the potato 

 such a valuable crop in cold countries like Norway and 

 Iceland, where the seasons are too short to admit of the 

 slow process of developing the plant from the seed. 



193. The Bulb is a form of underground stem reduced 

 to a single bud. Get the scaly bulb of a white garden lily, 

 and sketch it from the outside and in cross and vertical 

 section. Compare it with the scaly winter buds of the oak 

 and hickory or other common deciduous tree. Make an 

 enlarged sketch of the latter on the same scale as the lily, 

 and the resemblance will at once become clear. The 

 scales of the bulb are, in fact, only thick, fleshy leaves 



277. Scaly 278. Scaly bulb of 

 bud of oak lily (GRAY), 



enlarged. 



279. Bulblets in the axils 

 of the leaves of a tiger lily 

 (GRAY). 



closely packed round a short axis that has become dilated 

 into a flat disk. From the terminal node of this trans- 

 formed stem, i.e., the center of the disk, rises the flower 

 stalk, or scape, as it is called, of the season. After blos- 

 soming, the scape perishes with its bulb, and their place is 

 taken by new ones which are developed from the axils of 

 the scales, thus revealing their leaflike nature. 



That bulbs are only modified buds is further shown by 

 the bulblets that sometimes appear among the flowers of 

 the onion, and in the leaf axils of certain lilies. They 

 never develop into branches, but drop off and grow into 

 new plants just as the subterranean bulbs do. 



194. Tunicated Bulbs. Compare an onion or a hya- 

 cinth bulb with a lily bulb. In what respect does it differ 

 from the lily bulb ? Pull off the outer layers, which have 



