CHAP. II. 



STEM. 53 



The Stem has received many names; such as caudex 

 ascendens, caudex irdermedius^ culmus, stipes, truncus, and truncus 

 ascendens. It always consists of bundles of vascular and woody 

 tissue, embedded in cellular substance in various ways, and 

 the whole enclosed within a cuticle. Tlie manner in which 

 these parts are arranged with respect to each other will be ex- 

 plained hereafter. The more immediate subject of consideration 

 must be the parts that are common to all stems. 



1. Of its Parts. 



Where the stem and root, or the ascending and descending 

 axes diverge, there commences in many plants a difference 

 of anatomical structure, and in all a very essential physiolo- 

 gical dissimilarity ; as will be hereafter seen. This portion of 

 the axis is called the neck or collum, {coarcture of Grew, noeud 

 vital oi Lamarck, limes communis, or fundus plantcB, of Jungius,) 

 and has been thought by some to be the seat of vegetable 

 vitality ; an erroneous idea, of which more will be said in the 

 next book. At first it is a space that we have no difficulty in 

 distinguishing, so long as the embryo, or young plant, has 

 not undergone any considerable change; but in process of 

 time it is externally obliterated ; so that in trees of a few years' 

 growth its existence becomes a matter of theory, instead of 

 being actually evident to our senses. 



Immediately consequent upon the growth of a plant is the 

 formation of leaves. The point of the stem from whence these 

 arise is called the node [geniculum, Jungius), and the space 

 between two nodes is ca\[ed am internode {merithallus, Du Petit 

 Thouars). In internodes the arrangement of the vascular and 

 woody tissue, of whatever nature it may be, of which they are 

 composed, is neai'ly parallel, or, at least, experiences no hori- 

 zontal interruption. At the nodes, on the contrary, vessels 

 are sent off horizontally into the leaf; the general develope- 

 ment of the axis is momentarily arrested while this horizontal 

 communication is effecting, and all the tissue is more or less 

 contracted. In many plants this contraction, although \% 

 always exists, is scarcely appreciable ; but in others it takea 



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