H. Doc. 181. 



Plate XXIV. 



c 



G 



E 



Tangential Sections of Pinus t>cda, heterophylla, and glabra. 



A, Pinus heterophylla Radial and tangential sections of a transverse resin duct; r. d , resin duct; m. r. medullary ray; tr., tracheids of 



the medullary ray; p., parenchyma cells of the tame; c Jr., common tracheids or wood fibers. 

 B-G, Pinus glabra. B, tangential section of a transverse resin duct and parts of three fibers; b. />., bordered pit; other letters as above; 



C-G, tangential sections of medullary rays, of which E is made up of tracheids only, while D is a '" triple" ray 

 jET, Pinus t^da. Tangential sections of medullary rays in spring and summer wood. 

 Original magnified *;<*, illustrations about 3 i 10 . 



