18 BULLETIN 545, U. S. DEPARTMENT OF AGRICULTURE. 
In the region studied this species has a wide distribution. It 
occurs most abundantly and grows most luxuriantly in the Canadian 
zone, though it is met with in a variety of situations in both the upper 
and lower contiguous zones. In fact, the tendency of slender hair 
grass to adjust itself to various sites is a marked characteristic. In 
the well-aerated, finely disintegrated, basaltic soil of the plateaus in 
the Hudsonian zone this species does not wilt notably until the 
water content of the soil falls to between 8.5 and 10.0 per cent — a 
relatively low figure. On the other hand, simultaneous drought tests 
conducted in soils rich in organic matter, and where the plant had 
had access to a high per cent of soil water at all times, resulted in 
destructive wilting of the plant when the soil-water content was as 
high as 15 per cent. In moist situations a meager root system is 
developed, and on dry sites, while the root rarely penetrates deeply 
into the soil, it spreads over considerable surface. 
The flower stalks begin to appear about July 10 in the drier situa- 
tions, and a week or so later in moist places. By August 1 the 
majority have put in their appearance. Mature seeds are found as 
early as August 5, while the bulk of the seed crop is matured by 
August 25. The tests made for seed vitality were confined to the 
year 1909, and showed an average of 41.5 per cent. On lower ranges 
somewhat higher figures were obtained, 56.5 being the maximum. 
The grazing value of this plant is relatively low, and in this respect 
it does not compare favorably with tufted hair grass. Owing to its 
shallow roots the plant is frequently pulled up. Sheep grazing on 
this plant, especially early in the season when the soil contains a 
high per cent of moisture and the roots are readily pulled out, start 
masticating the leaf blades, but usually expel them when they find 
that roots and clinging dirt form the dessert to their diet. After a 
few experiences of this kind they crop it but little. Since the tussock 
is small, horses often pull up the entire tuft, and after eliminating the 
greater part of the clinging dirt by shaking it vigorously and rubbing 
it upon the ground, sometimes devour the plant. After about 
August 15 the leaves become air dried, and slender hair grass is then 
disregarded as a forage plant by all classes of stock. 
Another species known as black hair-grass (D. atropurpurea) occurs 
in scattered stand in open situations throughout the Hudsonian zone. 
Being restricted to high elevations (it rarely occurs beiow 6,500 feet), 
the flower stalks are not seen until July 15 and they continue to be 
produced until about August 25. No seed is matured until about 
September 1 and very little fertile seed is developed even in most 
favorable seasons. Reproduction takes place vegetatively by mean-E 
of offshoots arising from root stocks. 
