FOREST TREES OP THE PACIFIC SLOPE. 223 



chosen here is derived from the technical name Salix longifoUa, which was used 

 for it until it was found to he antedated by S. fluviatilis. 



A slender tree under 25 feet in height, with a narrow, compact crown of short, 

 slim, nearly tipright branches ; sometimes from 40 to 50 feet high and from 18 to 20 

 inches in diameter. A large part of the trunk is clear of branches. Over much 

 of its range it is only a reed-like shrub growing in very dense thickets 6 or 8 

 feet high. The closely scaly bark is very thin (usually less than one-fourth of 

 an inch thick), and dark grayish brown, with a faint reddish tinge; smooth on 

 small stems. Mature leaves (fig. 91) are pale yellowish-green, the under surface 

 lighter than the upper, smooth on both surfaces, and from about 3 to 5 inches 

 long. A variety of this species, Salix fluviatilis argyrophylla (Nutt.) Sargent, is 

 distinguished by the dense coating of silky hairs on its leaves and seed capsules; 

 while another form, >S'. fluviatilis exigua (Nutt.) Sarg., is characterized by its 

 very narrow leaves, If to 2f inches long by one-fourth to one-third of an inch 

 broad. Both of these varieties range from northern California through the 

 Southwest to Texas. ' 



Wood, pale reddish brown, light, firm, and rather elastic. It is of no economic 

 value. 



The longleaf willow is one of the most useful of its kind for retaining moist 

 sand bars and the erodable banks of streams which flow through rich bottoms. 

 It forms the densest of pure thickets, and propagates itself largely by shoots 

 from a mass of running roots, as well as by its seed, quickly occupying every 

 available strip of moist sand. 



Longevity. — Not fully determined. Stems from 2 to 3 inches in diameter are 

 from 9 to 14 years old. 



RANGE. 



Quebec (Lake St. John and Island of Orleans i and southward through western New 

 England to the Potomac River ; northwestward to the Arctic Circle (valley of Mackenzie 

 River) and British Columbia and California; southward in the Mississippi River basin 

 to northern Mexico and Lower California. 



OCCURRENCE. 



Sand bars bordering lowland streams, ponds, and lakes, in moist or wet sand and 

 gravel, overlaid with silt, which this willow's dense reed-like stems retain. Forms exten- 

 sive pure thickets and patches, in which cottonwood is sometimes mingled. 



Climatic Conditions. — Similar to those of aspen at lower levels. 



Tolerance. — Very intolerant of shade. 



Reproduction. — Exceedingly prolific seeder. Crowded masses of seedlings the first 

 tree growth to hold wet bars and muddy shores. Strikingly even-aged stands character- 

 istic of reproduction. 



Silverleaf Willow. 



Salix sessilifolia Nuttall. 



DISTINGUISHING CHARACTERISTICS. 



Silverleaf willow is generally known only by the name of " willow." In gen- 

 eral appearance, and in the form of its leaves, it closely resembles longleaf wil- 

 low, particularly the variety argyrophylla. It is sometimes 20 or 25 feet high 

 and from 8 to 10 inches through, but usually it is a slender shrub from 6 to 10 

 feet high. The grayish-brown bark of larger trunks is from one-third to one- 

 half an inch thick, with irregular shallow seams. Mature leaves (fig. 92). about 

 2 to 44 inches long by about one-fourth to one-third of an inch wide, sometimes 

 narrower, are light pea-green, smooth or minutely hairy on the upper side, and 

 with white, silky hairs beneath. Midveins of the leaves, lemon yellow, and the 

 short thick stems minutely hairy. 



The distinctive characters of this willow are not fully worked out. Many 

 forms of it so closely resemble »Sf. fluviatilis argyrophylla, with which it may 

 occur, that they can be distinguished only with great difficulty. Further careful 

 field study is required for both. 



