146 The Stem — Strictures [April, 



These buds are called nodes, and the spaces between ihexn,vit€rnodes. 

 The stem then may again be defined as a successive development of 

 leaf buds, iu a longitudinal and lateral direction. 



Stems receive diiferent names, according to the nature and char- 

 acter of the plant. In ordinary herbaceous plants, the stem is called 

 caulis; ux i-rcQ,^, truncus ; in shrubs, caudex ; in grasses, culm; in 

 palms and ferns, stipe. 



When the stem is woody, and continues to increase indefinitely, 

 we have either trees or shrubs ; trees when there is but one stem, 

 shrubs when there are several stems, mostly of equal size, springing 

 up together from the ground. It is the ligneous stem to which we 

 would chiefly direct our attention. As to external forms and char- 

 acteristics, in some plants the stems are cylindrical ; in others, com- 

 pressed ; in others, quadrangular ; solid in some, tubular in others, 

 and jointed or knotted in others; naked in some, and leafy in oth- 

 ers ; simple in some, and compound and branched in others ; robust 

 in some, and slender in others ; upright in some, nodding in others, 

 and decumbent in others ; rigid in some, and flexuous in others ; 

 self-supported in some, climbing in others, and creeping in others. 



Stems with respect to structure are either exogenous, viz. : increas- 

 ing indefinitely by layers upon the outside, as in most ligneous stems, 

 or endogenous, when the bundles of vascular tissue are produced in 

 definite fasciculi, converging toward the interior, all additions be- 

 ing constantly made within, as in the cornstalk. The acrogenoiis 

 in which the vascular bundles are all developed simultaneously, and 

 not in succession, the elongation of the stem depending on the 

 union of the bases of the leaves, or the petioles, and the extension 

 of the growing point or summit. These are the principal distinc- 

 tions. In our further remarks, we shall confine ourselves to the 

 exogenous or dicotoledonous stem, the type of most trees in the 

 temperate climate, erabracicg both the cellular and vascular systems; 

 the cellular system consisting of the outer bark, the medullary raps 

 and the pith ; the vascular, the inner bark, the woody layers, and 

 the medullary sheath. Some persons in discussing vegetable physi- 

 ology would range all nature in search of what the ancients vainly 

 attempted to find, a itniversal principle of things; not recognizing 

 the fact that every order, every class, every genus, every species, 

 has its own nature and its own laws. He who would attempt to 

 simplify where nature has not, will introduce only confusion, and 

 darken council by words without knowledge. 



