118 



BOTANY. 



Fig. 108), and exterior to this is the bundle sheath (u, Fig. 

 108). 



147. In Gymnosperms and Dicotyledons the fibro-vascu- 

 lar bundles of the stems have a structure essentially like that 

 of Ricinus communis, described above. In them it is evi- 

 dent at a glance that the bundle is divided into two some- 

 what similar portions, an inner and an outer, by the cam- 



Fig. 107. Longitudinal radial section of the flbro-vasrular bundle of the hypocpt- 

 yledonary stem of Ricinus communis (the transverse section being shown in Fig. 

 106). r, parenchyma of the primary cortex ; ffs, bundle sheath ; m, parenchyma of 

 the pith ; 6, bast fibres ; p, phloem parenchyma ; c, cambium ; the row of cells be- 

 tween c and p is afterward developed into a sieve-tube this and c constitute the 

 soft bast ; , the first-formed narrow spiral vessel ; from s the development of the 

 xylem portion of the bundle is toward t ; s', wide spiral vessel ; I, scalariform ves- 

 sel ; t, f, wide pitted vessels ; q, the absorbed septum ; fi". h 1 ". tracheldes (?) ; h. A', 

 forms of cells apparently intermediate between pitted vessels and tracheldes. Highly 

 magnified. After Sachs. 



bium zone. Nageli,* who first pointed out these divisions, 

 named the inner one the Xylem portion, because from it the 

 wood of the stem is formed ; the outer he named the Phloem 

 portion, for the reason that it develops into bark.f In 

 some cases the similarity between the structure of xylem 



* " Beitrage zur Wiesenschaftlichen Botanik," 1858. 



t Xylem from vAoi>, wood ; Phloem from Greek ^Xoiog , bark. 



