IMPORTANT RANGE PLANTS. 55 
SUMMARY. 
ECOLOGICAL REQUIREMENTS. 
The figures given in Table 2 represent the relative water require- 
ments of the different important forage plants studied. 1 Owing to 
the importance of having the plants advanced to as nearly the same 
point of development as possible when the drought tests were made 
aerial conditions were slightly different. The error due to this fact, 
however, is very largely offset by the duplication of the tests in the 
case of virtually all species. 
It is a well-established fact that the amount of moisture remaining 
in the soil when the plant wilts beyond recovery is determined by 
the physical structure of the substratum. The object in making the 
wilting coefficient determinations, then, is principally to show (1) 
that certain species occupy quite different soil types, and (2) that 
the soil types (textures) are widely contrasted as shown by the 
notable difference in the wilting coefficients for the various species. 
For example, mountain bunch grass (Festuca viridula) does not wilt 
seriously in the soil in which it characteristically grows until the 
water content is reduced to between 7 and 9.5 per cent. This plant 
is adapted to coarser and less rich soils than is mountain onion 
(Allium validum), for example, which is confined to exceptionally 
black, mealy soils, and which wilts beyond recovery when the soil 
moisture content drops to between 14 and 16 per cent. Owing to 
the relatively small amount of moist soil found in mountain range 
lands, it is evident that a species like mountain onion would not 
occur nearly as abundantly as mountain bunch grass. 
As a means of comparing habitat requirements, the species are 
grouped in three classes as follows : 
Class A, plants of high moisture requirement — those inhabiting 
saturated soils, such as open marshes, wet meadows and bogs; class 
B, plants of medium moisture requirement — those inhabiting rela- 
tively heavy soils which are saturated during the early part of the 
season, but later contain a medium amount of moisture; and class C, 
plants of low moisture requirement — those occurring in well-drained 
lands, open glades, and exposed situations. 
It will be observed that practically three-fourths of the most 
valuable forage species are dry-land plants. This fact is of high 
economic importance, since the major portion of the range lands are 
well drained and afford conditions favorable only to plants which 
are comparatively drought resistant. 
It is noted that a few species fall under more than. one head so far 
as concerns -their habitat requirements — that is, they are not strictly 
1 A resume of the potent climatic factors under which these tests were conducted was published in the 
Journal of Agricultural Research, Vol. Ill, No. 2, 1914, "Natural Revegetation of Range Lands Based upon 
Growth Requirements and Life History of the Vegetation," pp. 95-102. 
