296 Proceedings Port. Soc. Nat. Hist. 



must be res]3onsible for their absence from our area. A 

 glance at the map shows the answer. In the Penobscot Bay 

 region the coast is more broken up and the islands are farther 

 removed from the mainland and from one another than any- 

 where else along the Maine coast. This condition has been 

 more pronounced in the past than it is at present and it has 

 been impossible for many plants w^liich are present on the 

 mainland to bridge the gap to the outlying islands. 



THE OEIGIX OF THE XATIVE FLORA 



Any discussion of the origin of the native flora of the 

 eastern Penobscot Bay region is naturally limited in scope, 

 since all vestiges of the pre-glacial flora were presumably 

 destroyed during the Ice Age. Wliatever the nature of this 

 pre-existing floni, whether similar to that of the present time, 

 or showing more southern tendencies owing to a warmer 

 climate, it must have been driven out of the region by the 

 advent of the ice. A portion of this flora was probably 

 forced into the sea, where it perished, Init another part Avas 

 driven south and had reached ISTew Jersey and the southern 

 Appalachians before the advance of the glaciers was checked. 



Upon the retreat of the ice at the close of the Glacial 

 Period these nortliern plants began to follow back to their 

 old homes from these centers of distribution along the Ap- 

 palachians, for the most part '^'falling back into zones which 

 long environment had impressed upon them."' Adams^ con- 

 ceives of this northward migration' as occurring in waves. 

 The first of these waves consisted of the Arctic-alpine species 

 which were able to live at the very edge of the ice-sheet in a 



1. Brav. The Development of the Vegetation of New York State. 



N. Y. State Coll. For. Tech. Pub. 3 (1915). 



2. Adams. Postglacial Origin and Migrations of the Life of the 



Northeastern United States. Jour. Geog. 1: 303-310, 352-357 

 (1902). 



