OF THE ORGANS. 51 



A bulb (buldus), is a thickened, and commonly a spherical 

 or oval-shaped root, the solid central body of which is con- 

 tained within scales that lie upon one another, and between 

 which the stem, or shaft, rises ; (289.) 



II. The Stem. 

 66. 



Under the name Stem (tmnciis), we understand, generally, 

 that pai't of the plant which rises above the ground, and from 

 which all the other parts are evolved. 



In particular, it is called the stalk (caulis), when it is more 

 or less of a herbaceous nature. A plant which has a stalk is 

 called caulescens ; one in which it is wanting, is called acmiUs. 



67. 



Tree-like stems (trimci arbor ei), and trees {arhot'es), arc 

 those plants which have a simple and woody stem. 



In sections of woody stems we distinguish various parts, 

 which commonly lie in concentric layers within one another, 

 namely, 



1. The rind (cortex), the outer part of which, covered by 

 the epidermis {epidermis), is for the most part brown, grey, 

 or of some similar colour ; the inner part is entirely cellular, 

 and of a green hue. 



2. The inner bark {liher), is an apparently fibrous, whitc- 

 ish, and very flexible part, which lies under the rind. 



3. The soft-wood {alburnum)^ or the layer of young wood, 

 which approaches nearer to the nature of the inner bai'k, by 

 its brighter colour and greater flexibility. 



4. The wood {lignum), distinguished by its hardness and 

 cross-joinings, or bundles of rays {radii corticales). 



5. And, lastly. The pith {medulla), apparently of an entirely 

 cellular structure, and in old plants either entirely gone, or 

 only remaining as a thin, almost inorganic, brown kernel ; 

 (291.) 



D2 



