PLATE XXI. CROSS SECTIONS. 



A, PINUS T.EDA, 1 f-. r. d., resin dnct; . c., secreting cells; m. '., medullary rays; a, section of transverse trarhrid of 

 ray ; 6, the ray leaves the plain of the section at this point, small parts of it reappearing further on ; c, simple 

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

 /, flattened terminal part of a tracheid. 



K, PINUS HETEROPHYI.LA, i ? a . p. TO., springwood; mi. >., summerwood ; a-b, part of a row of traclieids forim-d 

 during one season; c, terminal parts of tracheids; d, bordered pit in spriugwood; e, same in summerwood; 

 other letters as in A. 



C, Pixus GLABRA, i ^ a . c, row of tracheids doubled; other letters as in B. 

 Originals, all *?". 

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