PINUS 



3t 



1. Resin ducts numerous, close to the surface; 



strengthening cells epidermal. 



a. Leaves over 1 dm. long, bundles close to- 



gether 



b. Leaves less than 1 dm. long, bundles widely 



separated 



( 1 ) Bundles embedded in sclerenchyma, epi- 



dermal cells nearly square 



(2) Bundles not surrounded by scleren- 



chyma, epidermal cells radially 

 elongated 



2. Resin ducts 2, in the midst of parenchyma; 



strengthening cells beneath the epidermis, 

 a. Leaves over 1 dm. long, 

 b. . Leaves under 5 cm. long, 



P. resinosa 



P. silvcstris 



P. mo n tana 



P. Laricio austriaca 

 P. Banksiana 



"PIWK^iana 



monTana 



I . blli/esfns 



Cross-sections of leaves of species of Pinus; diagrams x20, detail 

 of epidermis and the layers immediately beneath it xl50. In the diagrams 

 the sclerenchyma layer is heavily shaded. 



