122 IX. THE DICOTYLEDONOUS STEM HERBACEOUS TYPES. 



the surface of the stem ; in the interior, through the stretching 

 apart and destruction of the cells of the central portion of [the 

 pith, the stem is hollow. The vascular bundle gives the same 

 general impression as that of the Monocotyledons ; the same 

 parts are recognisable in the same order. The xylem portion [at 



FIG. 45. Cross-section through a vascular bundle from the runner of Ranunculus 

 repens. s, spiral vessels ; m, vessel with bordered pits ; c, cambium ; v, sieve-tubes ; 

 vg, sheath ( x 180). 



its inner edge consists of thin- walled wood parenchyma, in which 

 are a few more or less disorganised protoxylem elements ; then fol- 

 low gradually broadening spiral vessels, or vascular trachei'des (Fig. 

 45, s). Farther outwards succeed vessels with obliquely elongated 

 pits, and then the same with typically constructed bordered pits 

 (m), that is, in which the pit broadens out to its base, so 



