1903] FLORA OF NORTH CAROLINA 247 
recourse to the movement of glaciers southward during the ice 
age. It appears to the writer that the alternation of cold and 
warm periods is not necessary to account for the facts described 
above. An attempt is made in what follows to outline an alter- 
native hypothesis which appears to be a more satisfactory expo- 
sition of the case. The elevation of the southern Appalachian 
region from the Cumberland base level satisfactorily accounts 
for the differentiation of the corresponding mountain and coastal 
species. The species now found on the mountains adapted 
themselves to the higher elevations, and, being more plastic, 
were wrought upon by the forces which were and are at work in 
the gradation of the southern Appalachian region. For no fact 
in biology is better known than the capacity of some species to 
endure a wide range of physical conditions, while others are 
fatally sensitive to comparatively slight differences cf environ- 
ment. The modification of the species above mentioned was 
influenced by the rapid change in the physiography and topog- 
raphy of the country, and not by the glacial ice-sheet, which 
during a late geologic epoch covered the whole of North 
America. The oscillations of level are known to have taken 
place, and it is conceivable that the progenitors of the austro- 
riparian plants of the mountains and coastal plain, specifically 
identical, mingled when the country was a level peneplain, 
becoming differentiated as the elevation of the land became more 
marked. The distribution of plants which represent the charac- 
teristic flora of Eocene and Miocene times is thus accounted for. 
We have then, in the physiographic changes which have 
taken place in this mountain region, an explanation of the 
peculiarities of the flora of the southern Appalachians, which 
displays certain anomalies of distribution and isolation of mono- 
typic plants. The presence of Hudsonia montana Nutt. on the 
summit of Table Rock is thus explained Table Rock is an 
undenuded remnant of a former peneplain, and it is likely that 
Hudsonia montana Nutt. was once more extended in its distribu- 
tion, but has been isolated by the erosion of the larger part of 
the plain on which it formerly grew in abundance. Dicentra 
9 Collected there by Dr. John K. Small. 
