PLATE XXI.— CROSS SECTIONS. 



A, Pints t.eda, 'f. i: d., resiu duct; s. c, secreting cells; m. r., medullary rays; a, section of transverse tracheid of 

 • ray ; ft, tbe ray leaves the jilaiu of the section at this point, small parts of it reappearing further on ; c, simple 



pits connecting parenchyma cells of the ray; rf-e, jiart of a row of tracheids formed during one season; 

 /, flattened terminal part of a tracheid. 



B, PiNUS HETEROPHYLLA, ^V". sp. w., springwood ; sii. 10., summerwood; a-b, part of a row of tracheids formed 



during one season ; c, terminal parts of tracheids; (?, hordered pit in springwood; e, same in summerwood; 

 other letters as in J. 



C, PiNts GLABRA, -"^p. c, TOW of tracheids douhled; other letters as in B. 



Originals, all ■^"''. 

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