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- 



h I, 



Pig. 107.-Longitndinal radial section of the fit 



- - 



it (the transverse section being shown in Fig. 

 cortox ; 0, bundle sheath ; in, parenchyma o 



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

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

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

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

 pome cases the similarity between the structure of xylem 



* " Beitrage zur Wissenschaftlichnn Botanik," 1858. 

 f Xylem from i ; /oi<, wood ; Phloem from Greek ^ot 



bark. 



