lis 



BOTANY. 



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

 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.— Lrnigitiidinal radial section of the flliro-vasralar bundle of the hypocot- 

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

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

 the pith ; 6, liast fibres ; p, phloem parenchyma : c, cambium ; the row of ceils be- 

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

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

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

 sel : /, t^, wide pitted vessels ; g, the absorbed septum ; A". A'", tracheldes (?) ; A, A', 

 forms of culls apparently intermediate betwi en pitted vessels and tracheldea. 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 Wissenschaftlichen Bntanik," 1858. 



•)■ Xylem from (v^ov, wood ; Plilciem from Greek 0Xoi6{, bark. 



