THE STEM, OR ASCENDING AXIS. 



35 



herbaceous plants. " Halm" is a term used in England with the same 

 signification. Caulescent and acaulescent are convenient terms denot- 

 ing, the former the presence, and the latter the absence of the caulis or 

 aerial stem. 



170. THE CULM is the stem of the grasses and the sedges, generally 

 jointed, often hollow, rarely becoming woody, as in cane and bamboo. 



171. THE TRUNK is the name of the peculiar stems of arborescent plants. 

 It is the central column or axis which supports their branching tops 

 and withstands the assaults of the wind by means of the great firmness 

 and strength of the woody or ligneous tissue with which it abounds. 



172. VARIOUS FORMS. The trunk is usually seen simple and columnar 

 below, for a certain space, then variously dividing itself into branches. 

 Here it is cylindrical, straight and erect, as in the forest pine ; prismatic 

 often, as in the gum-tree ; gnarled and curved, as in the oak ; or inclined 

 far over its base, as in the sycamore. 



S B 



46. S, Spruce. B, Beech. E, Elm ; to illustrate excurrent and solvent axis, 



173. IN DIVIDING ITSELF INTO BRANCHES we observe two general modes, with 

 their numerous variations, strikingly characterizing the true forms. In the one, 

 named by Lindley the EXCURRENT, the trunk, from the superior vigor of its terminal 

 bud, takes precedence of the branches, and runs through to the summit, as in tho 



