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 lifnits of their ranges within or very near its 

 borders. The great wall of the Hoosac Plateau and the broad vaUey 

 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 en"\Tronment. 



A number of plants that occur in Berkshire County have not been 

 foimd farther north. These are either plants that require the warm 

 weU-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 County 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 the limestone areas of the north and west. These plants extend 

 either 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 distribution of some plants seems to be determined by none of 

 the factors of soil or warmth as at present understood. Such plants 

 are everywhere rare or local in their distribution. 



The changes brought about by the white man have profoundly 

 altered the original flora of the County. The clearing of the forests 

 and the cultivation of meadows and fields have changed the appear- 



