116 BOTANY. 



(h, h' , h", h'", Fig. 107). The last-named are clearly related 

 to the vessels which surround them, and from which they 

 differ only in their less diameter, and in having imperforate 

 horizontal or oblique septa. They are doubtless properly 

 classed with the Tracheides (see p. 84). On the outer side of 

 the tracheary portion just described lies a mass of narrow, 

 somewhat elongated, thin-walled cells, which constitute a 

 true meristem tissue, to which the name of Cambium* has 

 been given (c, c, Figs. 100 and 107). Next to the cambium 



Pig. 105. A very thin cross-section of the radial fibre- vaecular bundle of an old 

 adventitious root of Acorns calamus, g, the radial plates of tracheary tissue ; w, the 

 sieve tissue alternating with the plates of tracheary tit-sue ; , the bundle-sheath ; 

 the tissue in the centre of the bundle is sclerenchyma. x 145. After De Bary. 



lie, in order, sieve tissue and parenchyma; these do not occupy 

 separate zones, but are more or less intermingled, forming 

 a mass sometimes called the Soft Bast (y, y, y, Fig. 106, and 

 p, Fig. 107). The sieve tissue includes sieve tubes and 

 cambiform or latticed cells. In the extreme outer border of 

 the bundle is a mass of fibrous tissue (b, b, Figs. 106 and 107). 

 The layer of starch-bearing cells just outside of the last- 

 named tissue is the so-called bundle sheath. 



* Cambium, a low Latin word, meaning u liquid which becomes 

 orlutinous. The term wns introduced wh.-n the real structure of the 

 part to which it was applied was not understood. 



