50 MANUAL OP BOTANY 



are generally more or less thickened by deposition of nutritive 

 matters ; these, therefore, become reservoirs of nulriment for 

 the future use of the plant, just as in other cases the enlarged 

 stems and roots serve a similar purpose. The true bulb is only 

 found in Monocotyledons, as in the Lily {figs. 71 and 72), 

 Onion (fig. 73), and Tulip. The scales of a bulb, like the 

 leaves of a branch, often have new bulbs developed in their 

 axils [fig. 70, h) : these are called by gardeners cloves, and 

 their presence is an additional proof of the homology of a bulb 

 with a branch or bud. 



There are two kinds of bulbs commonly distinguished by 

 botanists, namely, the tunicated (fig. 73), and the scaly (figs. 

 71 and 72). The tunicated bulb is well seen in the Squill and 

 Onion (fi,g. 73). In this kind of bulb the inner scales, which are 

 thick and fleshy, enclose one another in a concentric manner, 

 and are covered externally by thin and membranous ones, 

 which form a covering or tunic to them, and hence the name 

 tunicated or coated, which is applied to it. In the scaly or 

 naked bulb, as it is also called (figs. 71 and 72), there are no 

 outer dry scales; but it is composed of thick, fleshy, more or 

 less flattened leaves, which simply overlap one another. 



The young bulbs- (cloves) (fig. 70, h), which are developed 

 in the axils of the scales of bulbs, either remain attached to 

 their parent, which they then commonly destroy by absorbing 

 all its stored-up nutriment ; or more commonly they become 

 separated in the course of growth, and form independent plants. 



In the axils of the leaves of certain plants, such as some 

 species of Lily (fig. 74, a, a], the Coralwort (Dentaria bulbi- 

 fcra), and Pilewort (Ranunculus Ficaria), small conical or 

 rounded fleshy bodies are sometimes produced, which are of the 

 nature of bulbs, and are hence called aerial bulbs from their posi- 

 tion, or bulbils or bulblets from their smaller size. They differ 

 from ordinary buds in their fleshy nature, and by spontaneously 

 separating from their parent, and producing new individuals 

 when placed imder favourable pircumstances ; and from true 

 bulbs by their small size and aerial position. These aerial 

 bulbs are not confined, as is the case with true bulbs, to Mono- 

 cotyledons, as may be seen by the examples given. 



d. The Oorm. — This form of stem, like the true bulb, is 

 chiefly found in Monocotyledons, as the Oolchicum (fig. 77) 

 and Crocus (figs. 75 and 76). It is an enlarged solid subter- 

 ranean stem, rounded in shape, composed of two or more inter- 

 nodes, and commonly covered externally by a few thin mem- 



