UNDERGROUND STEMS. 107 



of the fleshy bases of the leaves. But you will observe 

 that at the bottom there is a rather flat, solid part 

 upon -which these coats or leaves are 

 inserted, and which must consequently 

 be a, stem. Such a stem as this, with its 

 fleshy leaves, is called a bulb. If the 

 leaves form coats, as in the Onion, the 

 bulb is coated or tuhicated; if they do 

 ^sr- 139- not, as in the Lilies (Fig. 139), it is scaly. 



153. Tubers and bulbs, then, consist chiefly of masses 

 of nourishing matter ; but there is this difference, that 

 in the latter the nourishment is contained in the fleshy 

 leaves themselves, whilst in the former it forms a mass 

 more or less distinct from the buds. 



154. The thickened mass at the base of the stem of 

 our Indian Turnip (Fig. 34) is more like a tuber than a 

 bulb in its construction. It is called a com or solid 

 bulb. The Crocus and Gladiolus of the gardens are 

 other examples. The chief difference between the corm 

 and the ordinary bulb is in the relative space occupied 

 by the stem or solid part. In the former it is very much 

 greater than in the latter. The student should dissect 

 specimens of Indian Turnip, Crocus, Tulip, Hyacinth, 

 &c., when these differences will be readily apprehended. 



155. In the axils of the leaves of the Tiger Lily are 

 produced small, black, rounded bodies, which, on 

 examination, prove to be of bulbous structure. They 

 are, in fact, hulblets, and new plants may be grown from 

 them. 



156. Foliage-Leaves. These organs are usually 

 more or less flat, and of a green colour. In some plants, 



Fipr. 139.— Bulb of a Lily. 



