BOTANY. 



579 



stem ; but in the greater number the fructification 

 ,s lateral, that is, issuing from the axils of the 

 leaves. Of the first description is the common 

 American aloe, which is constituted of roots, a certain 

 number of leaves seated on the collet, and which are 

 developed seriatim from the circumference to the 

 centre, the last involving the fructification, which, 

 when produced, and the seeds ripe, the whole dies. 

 The second description comprises most of the palms ; 

 the evolution of these begins by the expansion of the 

 first exterior leaf, which is usually the least of all that 

 follows ; a second succeeds, with all the rest in train, 

 until all are expanded, or so long as the plant retains 

 vigour to bring them forth. The petioles, or foot- 

 stalks of the leaves or fronds, as they are called, 

 remain attached to the collet, and in time acquire a 

 woody consistence, and aggregately compose what 

 afterwards becomes the stem. This is conspicuously 

 the case in the genus Zamia, and in all the dwarf 

 palms, which, though they continue to evolve fronds 

 and flowers, never show any great elongation of 

 their axis. In the case of the lofty-growing palms, 

 the first evolution of their radical leaves is similar to 

 the dwarfs ; but with the consecutive development 

 of their leaves, an elongation of the axis com- 

 mences, and continues rising to the height of sixty 

 feet or more. This altitude is gained slowly, the 

 exterior of the stem being formed by the persisting 

 bases of the leaves, and being connected with each 

 other within, and with the collet, whence they all 

 spring, form the stem. Thus it appears that the 

 fronds are only expanded portions of the stem, the 

 whole being one uniform body of longitudinal fibres, 

 embedded in coarse cellular matter, hardening, and 

 becoming more compact by age. On a cross section, 

 there appear no consecutive layers or divisions of the 

 structure to indicate periodical additions, like those 

 of exogenous stems, and may be described as the 

 common petiole of the foliage and flowers. 



The annexed figures represent transverse and 

 perpendicular sections of dicotyledonous and moiio- 

 cotyledonotis stems. 



Of Branches. These are only subdivisions of the 

 trunk, being quite similar in structure. They differ 

 much in the manner of their divergence : being mostly 

 irregular, and spreading obliquely forward. Others, 

 as the pine tribe, are regularly branched from bot- 

 tom to the top in annual growths , the stem rising 

 erect, and the brunches stretching out horizontally in 



every direction ; when branches are so disposed, 

 they are said to be vcrticillate. In some cases the 

 branching is regularly alternate ; in others produced 

 in opposite pairs, alternately crossing, in which posi- 

 tion they are said to bo decussated. The branching 

 of trees constitutes their chief beauty : the lower and 

 lateral ones are mostly inclined to droop at the extre- 

 mities, and which in many sorts is most graceful. 

 The pendent spray of the weeping willow, birch, and 

 ash trees, are universally admired, being much more 

 beautiful than the stiff and formal forms of the larch 

 and Lombardy poplar. 



The Leaves. The foliar expansions of plants are 

 of several descriptions. The first to be noticed, are 

 the scales or winter coverings of the buds, hence 

 called hybernacula. They consist of dry membranous 

 scales seated at the base of the bud, over which they 

 are imbricated, and mostly deciduous when the bud 

 bursts. They are in some instances covered with 

 thick down ; in others with gum, as the balsam 

 poplar, or with resin, as in most of the order Coniferce. 

 Without such a provision as this, all the buds of trees 

 and shrubs in the regions of frost would be destroyed ; 

 but such is the protection afforded by hybernacula, 

 that they can bear thirty degrees of frost without 

 injury. 



The StipuUz are the next leaf-like expansion to 

 be noticed : they are sometimes single, but very 

 frequently double, and situate at the base of the 

 petiole, or leaf-stalk, one on each side, shown beneath. 



Stipulse. 



Sometimes they are united to the petiole, or 

 changed into prickles, as in the berberry. In some 

 of the grasses the stipulae is single, investing the culm 

 a little above the limb of the leaf, whence they are 

 said to be intrafoliaceous ; and when seated on the 

 outside of the petiole, they are said to be extrafoli- 

 aceous. In some plants the stipulae embrace the 

 stem like a sheath ; in others they invest the top of 

 the shoot, as in the fig tree. Stipule generally fall 

 with the leaves. 



The proper leaves are the grand ornaments of 

 plants ; from their numbers, position, and delicacy of 

 organisation, they are destined to effect some impor- 

 tant office in the economy of the plant. They are, 

 however, only temporary organs, being articulated 

 with the surface of the bark, and always seated upon, 

 or near the buds. Those of deciduous trees or shrubs 

 drop or wither as soon as the summer growth is over. 

 Some of both of those descriptions retain their leaves 

 to the second or third year, hence they are called 

 evergreens ; and some of the pines and firs retain 

 them for many years. 



Leaves are generally furnished with a foot-stalk 

 XX 2 



