ORGANS OF NUTRITIOK. 93 



teristic by -which a stem may be distinguished from a root. The 

 leaves will be treated of hereafter, but we have now to allude to 

 the parts of the stem from whence they arise, and to describe the 

 nature of buds, and the mode in which branches are formed. 

 . Leaves are always developed at regular points upon the sur- 

 <^pac6 of the stem, which are called oiodcs or ^imiply hiots {fig. 186, 

 "' c, c, c), and the intervals between them are termed internocUs 

 {fig. 186, d, d). Generally the arrangement of the tissue of 

 the stem at the nodes is somewhat different to that in the in- 

 t^rnodes ; thus at the node it exhibits a more or less contracted 

 or interrupted appearance, which arises from a portion of its 

 substance being given off to enter into the structure of the 

 leaf. This appearance is most evident in those cases where 

 the internodes are clearly developed, and especially if under 

 such circumstances the leaf or leaves which arise encircle the 

 stem, as in the Bamboo and other Grasses ; in such plants each 

 leaf causes the formation of a hardened ring externally {fig. 

 179,(6), and thus produces the appearance of a joint or articula- 

 tion, and indeed, in rare cases, the stem does readily separate 

 / into distinct portions at these joints, in which case it is said to 

 ^ he. jointed or articulated. 



Leaf-lnids or Bicds. — Under ordinary circumstances, as we have 

 seen, one or more buds are developed in the axil of every leaf 

 f {fig. 183, a, a). In like manner, the apex of a stem as well as 

 of all its divisions which are capable of further elongation, are 

 also terminated by a similar bud {fig. 185). Each bud, whether 

 lateral or terminal, is produced by an elongation of the paren- 

 ^ chymatous system of the stem or its divisions, and consists at 

 p^ first of a minute conical central parenchymatous mass, which is 

 connected with the pith (/^. 184, i) ; around this, spiral and other 

 vessels and wood-cells are soon developed, also in connexion 

 with similar parts of the wood, and on the outside of these, 

 in a cellular substance which ultimately becomes the bark, w.e 

 have little conical projections of parenchyma developed, which 

 are the rudimentary leaves {fig. 18'1). As growth proceeds these 

 parts become more evident, and a little conical body is ultimately 

 produced at the apex of the stem, or laterally in the axil of 

 leaves, and the formation of the bud is completed {fig. 185). 



The buds of temperate and cold climates, which remain dor- 

 mant during the winter, and which are accordingly exposed to 

 all its rigours, have generally certain protective organs developed 

 on their outer surface in the form of modified leaves, which are 

 commonly called scales. These are usually of a hardened tex- 

 ture, and are sometimes covered with a resinous secretion, as in 

 the Horsechestnut and several species of Poplars ; or with a 

 dense coating of soft hairs or down, as in some Willows. Such 

 scales, therefore, by interposing between the tender rudimentary 

 leaves of the bud and the air a thick coating of matter which is 



