Hill: Femhscot Plants. 21 o 



AusTEAL Regiox : comprising practically all of the United 

 States save the boreal mountains and the tropical lowlands. 



4. Transition zone — where the boreal and austral re-' 

 gions overlap, with southern species at their north- 

 ern limit and boreal species at their southern limit. 

 In the East this zone is represented by the Alleglia- 

 jiicui area which extends from Xew" England and 

 southern Ontario west to the Dakotas and south 

 along the Alleghanies to Georgia. 



5, Upper austral zone — consisting in the east of a 

 humid area- — Carolinian — which occupies a large 

 part of the Middle States at low altitudes, and on 

 the Atlantic coast extends from Chesapeake Bay to 

 southern Xew England with arms up the river 

 valleys. 



In the eastern Penobscot Bay region, where these zones 

 overlap, it is impossible in many cases to distingiiish clearly 

 between species which are Canadian and those which show 

 an Allcghanian trend. It is equally hard to draw^ a definite 

 line between the various sub-divisions of the Boreal Re- 

 gion as interpreted by jMerriam. Consequently it has been 

 thought best in the present discussion to consider the more 

 northern of the boreal plants, i. e., the Arctic-alpine and 

 Hudsonian, as distinct from the Canadian, and to place them 

 in a group by themselves (II). The Canadian plants are 

 united with the transitional Alleghanian forms in a second 

 group (III). Some of the Alleghanian plants, however, are 

 perfectly distinct from these northern species and are con- 

 sidered separately in Group IV. Another group (V) is 

 composed of southern species which are clearly of Carolinian 

 origin. 



To summarize then, the native flora of the eastern Penob- 

 scot Bay region will be considered under the follow'ing heads : 



