FLOEA OF THE YELLOWSTONE NATIONAL PARK. 11 



is found associated with P. flexilis, but ranges higher, being 

 found scattered or in bunches on rocky and exposed ridges and 

 summits at the upper limit of tree growth. It has been observed 

 as low as 7500 feet mingled with Pseudotsuga and Pinus Murray- 

 ana, but always in such situations with P. flexilis. Although 

 apparently common throughout the Park, it has not before been 

 distinguished from the allied P. flexilis. 



At a distance they closely resemble each other in general 

 habit, except for a bunched or fox-tail appearance of the leaves 

 of the former. Prof. Sargent says, that at Old Marias Pass in 

 northwest Montana, heretofore the most eastern station known, 

 P. albicaulis is readily distinguished from P. flexilis by the 

 milk-white bark ; but this characteristic which the author has 

 also observed in Washington Territory, is nearly wanting in the 

 Park. The chief points of difference lie in the cones ; those of 

 P. albicaulis when young are brown-purple, not green, with much 

 thicker scales. We have observed throughout the Park that 

 the cones of P. albicaulis, with hardly an exception, fall to pieces 

 soon after maturity, probably due, as Prof. Sargent suggests, to 

 the work of squirrels, so that a perfect cone is rarely found 

 upon the ground, while those of P. flexilis remain intact. The 

 leaves of the former are also shorter and stouter. The largest 

 specimen seen was 5 feet in diameter and 60 feet in height, on 

 Bison Peak, at an elevation of 9200 feet. These two pines form 

 nearly 10 per cent, of the forest area. 



Although the Yellow Pine, Pinus ponderosa, Dougl., var, 

 scopulorum, Engelm. (the Rocky Mountain variety), occurs on 

 all sides of the Park, it has not been detected within the borders, 

 although it would naturally be expected about some of the low 

 dry open areas. The greater portion of the region has too 

 great an altitude and rain-fall. 



The Douglas or Red Fir (Pseudotsuga Douglasii, Carr) is 

 found up to 9000 feet, generally scattered over the dryer grassy 

 ridges and slopes. Rarely it occupies exclusively small areas. 

 The slope immediately west of the Mammoth Hot Springs for 

 700 feet upward is covered with this species alone. The largest 

 trees observed had a diameter of 5 feet, b^ generally were 

 stunted and more or less decayed. 



The Balsam (Abies subalpina, Engelm.) ranks next to the 



