H. Doc. 181. 



PLATE XX. 



i t-su.iv 



r r.d. 



c 





mj-.-vf 



~ a 



TYPICAL CROSS SECTIONS OF PINUS T/EDA, HETEROPHYLLA, AND GLABRA. 



r. d., resin ducts; s. c., secreting cells; m. r., medullary rays; sp. it'., spring wood; n. u:, summer wood. 



A, PINUS TMDt. : a-b, transverse tracheids; c, simple pits; d-e, row of tracheids; /, flattened terminal of tracheid. 

 *. PINTS HETEROPHYLLA : o-fc, row of tracheids; c. terminal of tracheid; d-t, bordered pits. 

 C, PINUS OLABRA : a-6, single row of tracheids; c-6, same row doubled. 



