This means of determination serves also to show the close 

 relations existing between doubtful species. These will be dis- 

 cussed more fully under the species involved. So far I have 

 dealt only with the subfamily Abietineae, excluding in our range 

 the genus Juniperus. Good sections of the latter are so hard 

 to obtain that it is very doubtful if a practicable key for this 

 genus can be constructed on the basis of leaf-structure. The 

 ke^-s and descriptions of the species of the Central Rocky Moun- 

 tain region (as given in Coulter and Nelson's Manual) follow, 

 with diagrams where necessary. For the nomenclature I have 

 followed Sudworth, in his 1897 report on the "Arborescent 

 Flora of the United States." 



Family PINACEAE. 

 Leaves needle-like; fruit drj' cones. 

 Leaves scale-like or subulate; fruit (in ours) berries. 



Subfamily Abietineae. 

 Walls of the mesophyl intruded, giving the cells a lobed 



appearance. 

 Walls of the mesophyl not intruded. 

 Stomata present on one side onlj^ 

 Stomata present on all sides. 



Leaf strongh' 4-angled; bundle-sheath conspicu- 

 ous. 

 Leaf stronglj- 4-angled ; bundle sheath inconspicu- 

 ous. 



L PiNUS. 



Cross-section triangular or wedge-shaped. 



Xj-lem of bundle not at all divided. 



Stomata present on all sides. 



All the resin ducts usually next to dorsal side 



(see descriptions). 

 One resin duct usually found in the angle be- 

 tween the ventral sides (see descr.). 

 Stomata lacking on dorsal side. 

 Xylem of bundle divided. 

 Cross-section semicircular or crescentic. 



Xylem of bundle divided; ducts parenchymatous. 

 Widely divided. 

 Yery slightly divided. 

 Xj-lem of bundle undivided; ducts peripheral. 

 Stomata usually more than 12. 

 Stomata usually less than 12. 

 Cross-section circular. 



Abietineae. 

 Cupressineae. 



PiNUS. 



PSEUDOTSUG.\. 



PiCE.A.. 



Abies. 



I. P. flexilis. 



2. 



P. 



albicaulis. 



3- 



P. 



aristata. 



6. 



P. 



ponder osa. 



5- 



P. 



Murray an a. 



6. 



P. 



ponder OS a. 



4- 



P. 



monophylla. 



4a. 



P. 



moyiophylla edulis. 



4- 



P. 



monophylla. 



