6 



varietal rank. As these two unstable differences are the only 

 definite ones given in the descriptions, there is no reason for 

 keeping the later published one as a species distinct from the 

 older. It is perhaps best to call the form in which all the leaves 

 are in bundles of 2 or 3 a variety, P. monophylla ediilis Jones, 

 and to call the forms with single leaves the true species. 



5. PiNUS MuRRAYANA Oreg. Com., in Murray Rep. Bot. Exp. 



Oreg. No. 740, t. 3. 1853. 



Tall (15-30 m.) and slender; leaves semiterete, about 5 cm. 

 long, in fascicles of two; cones small, adhering to the branches; 

 scales armed with slender, sometimes recurv^ed, prickles; seeds 

 winged. Lodge Pole Pine. 



Throughout the Rockies. 



This species can readily be distinguished from P. ponderosa 

 by the widely divided xylem, the xylem in P. ponderosa being 

 but slightly divided. 



6. PiNUS PONDEROSA Douglas, in Lawson, Man. 355 (1836); 



Comp. Bot. Mag. 2: iii. 1836. 



Usually a large tree, 25-40 m. high, 1-2 m. in diameter; leaves 

 in fascicles of 2 or 3 (usually 3), 1-2 dm. long, crowded brush-like 

 on ends of branchlets; cones 7-12 cm. long; scales thickened at 

 the outer end, bearing a recurved prickle; seeds brown, winged. 

 Rocky Mountain Yellow Pine. 



Throughout the Rocky Mountains. 



Distinguished from other species of this range by the xylem, 

 which is slightly divided. This includes the so-called Pinus 

 scopulorum (Engelm.) Lemmon, a species which is not essentially 

 different. 



II. PiCEA. 



Xylem of bundle not at all div-ided; 6-10 large heavy-walled 



strengthening cells at one side of bundle, in addition to the 



ordinary tissue. i. P. Engelmannii. 



Xylem of bundle slightly divided by one or two rows of larger, 



thinner- walled cells; no additional strengthening tissue 



present. 2. P. pungetis. 



