SUBTERRANEAN LEAF -BUDS, BULB, AND CORil. 



99 



lateral ones may be separated as distinct plants in the form of suckers 

 (surculi). The potato is a thickened stem or branch capable of 

 developing leaf-buds, which in their turn form aerial and subterranean 

 branches, the former of which decay annually, while the latter remain 

 as tubers to propagate the plant. Thus, in fig. 92, s s is the surface of 

 the soil, p a is the aerial portion of the potato covered with leaves, t is 

 the subterranean stem or tuber covered with small scales or projections, 

 as represented at T b, from the axil of which leaf-buds are produced. 

 This provision for a symmetrical development of axillary leaf-buds at 

 once distinguishes the tuber of the potato from fleshy roots, like those 

 of the Dahlia. 



194. Bulb. A good example of a subterranean bud occurs in the 

 Bulb, as seen in the Hyacinth, Lily, and Onion. This is a subterranean 

 leaf-bud covered with scales, arising from a shortened axis. From the 

 centre of the bulb a shoot or herbaceous stem is produced which dies 

 down. New bulbs, or cloves as they are called, are produced from 

 the subterranean axis. At the base of, the scales there is a flat- 

 tened disc, varying in thickness, which is formed by the base of the 

 buds, and which has sometimes been called the stem. The parts of 

 the bulb are seen hi fig. 207, where p marks the disc or round flat 

 portion formed by the bases of the lateral buds from which the fasci- 

 culated roots, r, proceed, e the scales or modified leaves, and /the true 

 leaves. In the vertical section (fig. 208), b is the new bulb formed like 



207 208 209 



a bud in the axil of a scale. The new bulb sometimes remains attached 

 to the parent bulb, and sends up an axis and leaves; at other times it 



Fig. 207. Tunicated bulb of Allium Porrum, or the Leek, r. Roots, p, A circular disc, or 

 shortened stem intervening between the roots and the bulbous swelling, e e. Scales, or subter- 

 ranean modified leaves. /, Upper leaves which become green. 



Fig. 208. Vertical section of the tunicated bulb of the Leek. The letters indicate the same 

 parts as in the last figure. 6, Bud situated in the axil of a scale, which, by its development, forms 

 a new bnlb. 



Fig. 209. Scaly or naked bulb of Lilium album, r, Roots, eee. Scales or modified under- 

 ground leaves, t, The stem cut. 



