518 BOTANICAL GAZETTE [JUNE 
Sedum stenopetalum, Potentilla concinna Rich., Carex stenophylla 
Wahl., Aragallus Lambertii (Pursh) Greene, Chrysopsis villosa 
(Pursh) Nutt., Comandra pallida A.DC., Arenaria Fendleri Gray, 
Artemisia frigida Willd., and A. canadensis Michx.; simultaneously, 
there is an incoming of such grasses as Muhlenbergia gracilis Trin., 
Danthonia Parryi Scribn., Festuca saximontana Rydb., Poa interior 
Rydb., and Koeleria cristata Pers. There results a xerophytic 
grassland which has been designated ‘“‘dry grassland.” It is a 
persistent and long-lived plant community. 
The dry grassland of Boulder Park has been the object of 
extended study by RAMALEY (14, 15, 16, 17). The association is 
preeminently one of coarse, gravelly, thin soils. Humus is con- 
spicuously scarce. The soil temperatures run high throughout 
the vegetative season, and the soil water content low, at times 
falling below the wilting coefficient. The area is well exposed to the 
winds, and snow does not accumulate to any extent. RAMALEY 
has shown that 70 per cent of the most important dry grassland 
plants are shallow rooted, and that 33 per cent of them-are rhizo- 
matous; moreover, many of those which do not bear rhizomes 
have much branched caudices. Practically 91 per cent of the dry 
grassland plants are perennial. These facts point to the extreme 
xerophytism of the habitat. . 
The dry grassland is an open community; bare ground composes 
about 15 per cent of the whole area during the month of July. 
There is ample opportunity for seeds to find open territory; but 
the life of the seedling is a precarious one. There is a lack of soil 
water, droughts are frequent in summer, the transpiration rate is 
high, and there is a lack of winter snow cover. These conditions 
exclude the invasion of trees and many mesophytic plants. 
Dry grassland has all appearances of being the ultimate vegeta- 
tion throughout the Park, under present climatic and physiographic 
conditions at least. However, slowly but surely it is being invaded 
in places by meadow; a series of dry years may see the drying up 
of meadow, the fragmentation of plant parts, and their removal 
by wind, thus reinstating the dry grassland stage. The resultant 
is a slow encroachment of dry grassland by mesophytic grasses and 
other herbs. As has been indicated, if physiographic and climatic 
