280 Proceedings Port. Soc. Nat. Hist. 



boriiii>- seaward islands are iinal)le to cross the intervening 

 space and so are absent from onr area. 



A considerable number of sub-arctic species, nevertheless, 

 are to be found on the outer headlands of the Penobscot Bay 

 islands. Growinii in humus or peaty turf are such plants 

 as: Enipeinnn ui(/rujit. often projecting out over the exposed 

 rocks in great mats; Juniperus liorizontalis, frequent on the 

 outer islands and also known from two stations at Brooklin, 

 some ten miles up the Bay; and T/icriniu in Vifis-Idaea. var. 

 minus, common on barren hills and outcrops as well. Other 

 species are much less frequent: Sediim roseum, grovring in 

 great profusion on cliffs at Placentia Island near Swans 

 Island, and on a rocky beach on Isle an Ilaut ; Iris se/osa. 

 var. ranadensis, on the crests of headlands at Black Point, 

 kSwaiis Island, a southward extension of range from Little 

 Duck Island;' and Arenaria groenlandica, at a single station 

 each on Deer Isle and Isle an Haut. 



The raised bogs back of the headlands, a characteristic 

 feature of this coastal strip to the eastward,^ are lacking in 

 Penobscot Bay or at most attain only a meagre development 

 and so are unable to support the plants common to such a 

 habitat. It is perhaps a signiiicant fact that most of the 

 sub-arctic plants which fail to reach our area are species of 

 these raised bogs or heaths, which would be unable to find 

 the necessary conditions for their existence even if they 

 should bridge the gap between ]\Iount Desert and the Penol)- 

 scot Bay islands. 



The r(X'kv beaches and brackish marshes also furnish a 

 decidedly l)oreal habitat for such plants as Carex innr'dinid, 

 Carex sfdi)i(i. var. kaiiegaiensis, Eh/mus arenarius, var. rU- 

 Josus, Coelo/jJeuruin actaeAJoHum and Mertensia marUinia. 



1. See Norton, A. H., Rhodora 15: 138 (1913). 



2. See Fernald & Wiegaud, Rhodora 12: 100. 



