Palmer — Flora of the Grand Falls Chert Barrens. 103 



dubia, Coreopsis lanceolata, C. tinctoria and Polygonum 

 tenue. Growing with these are also many plants of wider 

 distribution, evidently invaders from the dry woods and 

 prairies beyond. In number of species these far exceed 

 the "aborigines," although of the latter such plants as 

 Selenia aurea, Crotonopsis linearis and Coreopsis tinc- 

 toria sometimes prevail over limited areas almost to the 

 exclusion of all others. 



0\er the most exposed portions of the surface, where 

 the rock is almost destitute of soil and very little sus- 

 tenance is afforded such hardy pioneers of vegetable colo- 

 nization as Selaginella rupestris, reindeer moss and a 

 number of other lichens and mosses manage to maintain 

 themselves. Here, no doubt, the cryptogamist would find 

 an interesting field for study. 



As might be expected nearly all of the characteristic 

 plants of the more typical portions of the barrens are 

 annuals, with a few fleshy-rooted perennials, such as 

 Opuntia macrorhiza and the Talinums, especially adapted 

 to sustaining long periods of drouth. The life period of 

 many of the plants is shorter and the individuals are 

 much smaller than of the same species under normal con- 

 ditions. The perpetuation of some of them apparently is 

 dependent upon their ability to mature their seeds or 

 spores while the supply of moisture holds out. With the 

 hot sun beating down on the unshaded rock, the germina- 

 tion of the seed deposited in the thin rich soil, and the 

 subsequent development of the plants is hastened with 

 almost tropical rapidity. 



In a normally dry season the number of plants that can 

 be collected after mid-summer is very small. Of the an- 

 nuals a few grasses, such as Aristida basiramea and Era- 

 grostis capillaris, and such narrow leafed plants as Polyg- 

 onum tenue, Crotonopsis linearis and Isanthus brachi- 

 atus survive until late in the season. After the autumn 

 rains set in some of these seem to take on a new lease of 

 life, with Selaginella rupestris and the fleshy rooted 

 perennials. 



