118 



BOTANT. 



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- 



Pig. 107. — Longitudinal radial section of the filirn-vasfnlar bundle of the hypocot- 

 yledonary stem of Ricirms communit (the transverse pection being thown in Fig. 

 106). r, parenchyma of the primary cortex ; gs, bundle sheath : rn, parenchyma of 

 the pith ; &, hast fibres ; p^ phloem parenchyma ; c, cambinm ; the row of cells be- 

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

 soft hast ; .«, the first-formed narrow spiral vessel ; from s the development of the 

 xylem portion of the bundle is toward t ; s\ wide spiral vessel ; ^scalariform ves^^ 

 eel ; ^, *', wide pitted vessels ; g, the absorbed septum ; h". h'". tracheides (?) ; h, V, 

 forms of cells apparently intermediate between pitted vessels and ti acheldes. Highly 

 magnified. — After Sachs. 



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

 Tiamed 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 Wisgenschaftlichen Botanik," 1858. 



f Xylem from ivXov, wood ; Phloem from Greek ^/loidg, bark. 



