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 tine- 
toria sometimes prevail over limited areas almost to the 
exclusion of all others. 
Over 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, remdeer moss and a. 
number of other lichens and mosses manage to maintain 
themselves. Here, no doubt, the eryptogamist 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. 
