THE PINES OF MEXICO. 



CONSPECTUS OF THE MEXICAN SPECIES 



A. Fibro-vascular bundles of the leaves single ; bracts subtending the leaf- fascicles inserted 

 on prominent bases not decurrent on the branchlets ; cones symmetrical, opening at ma- 

 turity ; seed-wing absent, or present and variable ; walls of the tracheids of the medullary 

 rays of the wood not dentate ; cortex of young trees persistently smooth for many years. 

 Seed-wing wanting, umb-o of the cone-scales dorsal. 



Sheaths of the leaf-fascicles deciduous. 



Cones of few scales, subsessile, subglobose. i cembroides. 



Cones of several scales, long-pedunculate, cylindrical. 2 Pinceana. 



Sheaths of the leaf-fascicles persistent. 3 Nelsoni. 



Seed-wing persistent on the nut, umbo of the cone-scales terminal, 

 sheath of the leaf-fascicles deciduous. 



Stomata of the leaves ventral only, leaves serrate. 4 ayacahuite. 



St omata of the leaves dorsal and ventral. 



Leaves entire, seed-wings rudimentary. 5 flexilis. 



Leaves serrate, seed-wings efficient. 6 Lambertiana. 



B. Fibro-vascular bundles of the leaves constantly or irregularly double; bases of the bracts 

 subtending the leaf-fascicles, decurrent on the branchlets ; umbo of the cone-scales dor- 

 sal ; walls of the tracheids of the medullary rays of the wood dentate ; seeds winged. 

 Sheaths of the leaf-fascicles deciduous. 



Cones persistent, fructification triennial. 7 leiophylla. 



Cones deciduous, fructification biennial. 8 Lumholtzii. 



Sheaths of the leaf-fascicles persistent. 



Cones deciduous, dull or sublustrous. 

 Cones 4-8 cm. in length. 



Resin ducts of the leaves mostly medial. 9 teocote. 



Resin ducts of the leaves mostly internal. 10 Lawsoni. 



Cones 6-30 cm. in length, usually much larger than in 9 and 10, 

 resin ducts of the leaves medial. 



Cortex of young trees smooth. 1 1 pseudostrobus. 



Cortex of young trees rough. 



Prickle of the cone-scales weak and usually deciduous. 



12 Montezumae. 

 Prickle of the cone-scales stout and persistent. 13 ponderosa. 



Cones persistent, serotinous, lustrous. 



Base of seed-wing thickened, cones 5-10 cm. in length. 



Resin ducts of the leaves internal. 14 Pringlei. 



Resin ducts uniting hypoderm and endoderm. 15 oocarpa. 



Resin ducts medial. 



Leaves short, erect ; cortex of young trees per- 

 sistent, smooth and gray. 16 Greggii. 

 Leaves slender, pendent ; cortex of young trees 



deciduous, scaly and red. 1 7 patula. 



Base of seed-wing not thickened; cones 3-4 cm. in length, 

 resin ducts in the leaves medial; leaves in fascicles of 2, 

 3-8 cm. long. 18 contorta. 



