12 HARPER 



that of the rest of the continent) is due more to soil or to 

 climate. 



5. The glaciated region. The greater part of temperate Eastern 

 North America north of latitude 40 is covered with many feet of 

 glacial drift, obliterating most of the pre-existing geological and 

 topographic features. This is believed to be approximately con- 

 temporaneous with or even subsequent to the Columbia form- 

 ation of the coastal plain. The flora of the glaciated region 

 has several features in common with that of the coastal plain, 

 as the writer has recently pointed out, 1 and this is doubtless 

 due largely to the similarity in age. The older formations are 

 exposed at many points in the glaciated region, however, and 

 this gives a greater diversity to the flora than it would other- 

 wise have. 



(A few comparatively small areas of Triassic rocks, located 

 chiefly in New Jersey and North Carolina, have not been men- 

 tioned above because they are too limited in extent to have 

 any peculiar flora of their own. They are usually classed with 

 the Piedmont region, which they immediately adjoin.) 



Sufficient data are not yet available for estimating with any 

 degree of accuracy the number of indigenous species of plants 

 in the several natural divisions above outlined, and the pro- 

 portion of species endemic to each. In order to do this the 

 known ranges of all the species would have to be worked out in 

 terms of physiographic divisions, instead of political divisions 

 as has been customary hitherto, and that would require years 

 of study. It is perhaps safe to assume, however, that in the 

 coastal plain, between (but not including) the glaciated portion 

 in the northeast, the subtropical portion in the southeast, and 

 the arid portion in the southwest, there are in the neighborhood 

 of 3000 native species of flowering plants. The number of 

 endemic species assigned to a given region depends largely on 

 the interpretation of specific limits, but the coastal plain pro- 

 bably contains a larger endemic element than any one other 

 division, and perhaps as many endemics as all the rest of 

 temperate Eastern North America combined. 



1 Rhodora 7: 69-80. April, 1905. 



