QYMNUaPERMM. 



m 



^surface. In many cases oil or resin receptacles occur in, or 

 immediately beneath, the epidermis. 



516. — The fibro-vascular bundles are for the most part 

 of the collateral form, and in the young stem they are ar- 

 ranged so as to form an inner xylem cylinder ensheathed by 

 a phloem cylinder (Fig. 301). The xylem of these first- 

 formed bundles is composed of an inner mass of annular and 

 spiral vessels, which gradually pass outwardly into tracheides. 

 The phloem is mostly composed of an outer mass of bast 



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WHc^^^^nt 



Fig. .%!«.— CroPB-section throii£*h the new wood (/i-A). cambinm f x - x ), and bark 

 '(6-6) of the stem of Junimnta communifi^ made at Mie end ot Si'ptember. ra, «i, nie- 

 -duUary rays. In the tiarK are shown the layers of bast fibres, b, b. b. Magnified. — 

 After De Bary. 



fibres, which is bordered intei-nally by a mass of sieve tissue 

 (latticed or cambiform cells) and parenchyma. Between the 

 xylem and the phloem a layer of cells always remains as a 

 meristem tissue ; this constitutes the cambium layer of the 

 bundles (c. Fig. 301, B., and X-X, Fig. 301a). 



517. — The increase in the diameter of the stem takes 

 place by the multiplication of cells in the cambium layer ; 

 the cambium cells undergo longitudinal fission by the forma- 

 tion of partitions at right angles to the radii ; these new cells 



