HOFFMANN: FLORA OF BERKSHIRE COUNTY. 189 
Besides the factors above stated which determine the distribution of 
plants within their geographical range, there is the question of geo- 
graphical range itself which determines the flora of a given region. 
The past history of plant life on this continent is not well enough 
known to enable us to do more than guess at the different courses which 
plants have taken to reach the same region, but we do know of the 
plants of any given region that some are commoner to the north, south, 
east, or west, and we think of certain plants therefore as representa- 
tives of northern, southern, eastern, or western floras. Berkshire 
County is a particularly interesting field for the study of the distri- 
butional relationships of plants. Its flora contains a large proportion 
of plants that reach the limits of their ranges within or very near its 
borders. The great wall of the Hoosac Plateau and the broad valley 
of the Connecticut apparently form a barrier against the progress 
farther east of many plants which are found from Berkshire County 
far westward. The drier soil and lower elevation of the country 
south of Berkshire proves a barrier to the further progress of northern 
plants, or it may well be that these plants have been retreating north- 
ward, after the glacial waters were drained off and that the high land 
or bogs of Berkshire still offer a suitable environment. 
A number of plants that occur in Berkshire County have not been 
found farther north. These are either plants that require the warm 
well-drained country lacking to the north, or plants that occupy the 
ridges of the Alleghanies southward to Georgia and a very few that 
follow the coastal plain to Florida. 
A great number of plants characteristic of Berkshire Count >• are 
plants that need lime in the soil. Their range coincides with surpris- 
ing exactness with that of the ancient sea-floors which are now exposed 
in tlie limestone areas of the north and west. These plants extend 
eitlier from northern Maine through northern New Hampshire, 
Vermont and across New York, Ohio, and Wisconsin to Alaska, or 
south through Kentucky, Missouri and Kansas to Texas, according as 
they are plants that love warmth, or are plants of northern latitudes. 
The (listrilnition of some plants seems to be determined by none of 
the factors of soil or warmth as at present understood. Such plants 
are everywliere rare or local in tlieir distribution. 
Tlie changes brought about by the wliite man have jirofoundly 
ahered the original flora of the County. Tlu> clearing of the forests 
and the cultivation of meadows and fields haxi' changed the appear- 
