DRY GRASSLAND OF A MOUNTAIN PARK 251 



all of the plants under consideration are native. European 

 or other "weeds" do not enter into these plant communities; 

 indeed few of them are found anywhere in Boulder Park." 



SEASONAL ASPECTS 



The growing season in the dry grassland may be considered 

 as consisting of five periods. These, with notes on their most 

 conspicuous and characteristic plants are listed below. The 

 dates given as limits of the seasons are to be considered as merely 

 approximate. In exceptional years there may be a retardation 

 or an acceleration of one or two weeks. 



1. Prevernal period (May 1 to June 15). Important plants 

 in flower: Mertensia bakeri and Thlaspi purpurascens. During 

 the prevernal period the dry grassland is brown with the dead 

 herbiage of the previous year. The bluish-green leaves and 

 bright blue flowers of the low-growing bunches of Mertensia 

 are quite conspicuous. Indeed the prevernal might be called 

 the "blue" period. The Mertensia is found in old lake beds, 

 along stream terraces and morainic knolls, and in glacial de- 

 pressions; indeed everywhere in the dry grassland area. The 

 Thlaspi, a small, low, white-flowered plant of candytuft-Uke 

 aspect is more restricted, occurring chiefly on slopes. 



2. Vernal period, June 15 to July 1. Important plants in 

 flower: Cerastium occidentale, Antennaria arida, Antennaria aprica, 

 Carex stenophylla. This is a period of rapid change in the ap- 

 pearance of the dry grassland. The general brown color of 

 Spring only slightly modified by Mertensia and Thlaspi becomes 

 replaced by fresh green as the grasses and flowering herbs begin 

 a rapid growth. Chickweed {Cerastium occidentale) is scattered 

 nearly everj^vhere in the dry grassland area, although least 

 abundant in the hyperxerophytic portions on the one hand and 

 in the Danthonia society on the other. The species of Anten- 

 naria form mats that are conspicuous because of their woolly 

 leaves and white flowers (fig. 3). Since chickweed and the 



^ Elder, Mary. Esther, Roadside plants of a high mountain park in Colorado. 

 Torreya, 12: 175-80, 1912. 



