44 GRIGGS: OBSERVATIONS ON THE BEHAVIOR 
where the climatic conditions were locally favorable. This is 
undoubtedly frequently the case. Bessey’s* finding Adiantum 
Capillus-veneris near a hot spring in South, Dakota is a notable 
example. The presence of Betula lutea and some other northern 
plants in the deep cold ravines of the present area may be set 
down rather confidently as a local instance. I would not dare, 
however, to apply this explanation to more than seven of the 
twenty-five outliers listed above; for the others it seems clearly 
out of the question. 
For many of the plants which terminate here, especially those 
which I know best because their boundaries cross the area, it is 
quite beyond my power of analysis to discover any reason why they 
should find their limits where they do and not go a few miles fur- 
ther. The easiest explanation of my inability to fix upon the reason 
for the location of their termini is that there is no reason; that 
they do not occupy ranges fixed by climatic conditions but are in 
process of adjustment. Observation of these plants seems to 
indicate that competition with other plant species is more im- 
portant than climate in fixing the limits of their ranges. The 
case may be best presented by a few concrete examples: 
Silene rotundifolia is common in the crevices of rocks regard- 
less of exposure (not on “shaded banks’’) throughout the southern 
section of our area whence it extends southwa-d along the western 
slope of the mountains to Tennessee. It is common up to ‘“Cant- 
well Cliffs’’ but here it suddenly stops and has never been found 
further north. Suitable habitats, however, are by no means 
lacking. 
Aralia spinosa is another plant of this sort. This species is 
of such a character that he who travels the brush, whether he be 
botanist or not, is forcibly made aware of its presence wherever 
it grows. It is a common plant over most of the southern states 
reaching its northern limits in southern Illinois, the Sugar Grove 
area, and Pennsylvania. It is abundant in the valley of Queer 
Creek and in some places on Big Pine Creek, occurring on the 
higher slopes where the timber has been cut off. As already 
indicated its place in plant society has been greatly enlarged by 
the lumberman so that it is now much more common than formerly 
* Bessey, C. E. One thousand miles for a fern. Asa Gray Bull. 8: 2-6. 1900. 
