22 INTRODUCTION. 



always found difficulty in crossing it from the mainland. 

 This difficulty has had its effect in decreasing the Island 

 flora. 



Again, in the development of their flora the Cranberry 

 Isles have shown some peculiarities. These islands, once 

 doubtless a part of Mt. Desert, and through it connected 

 with the mainland, were later submerged, and then ele- 

 vated again to develop their flora independently of Mt. 

 Desert, except so far as the flora of the smaller area 

 came from that of the greater, then doubtless more 

 advanced in the renewal of its vegetation, owing to 

 its greater altitude and consequent earlier elevation. 

 That there was some independent development is well 

 shown by the fact that between the Cranberry Isles and 

 the adjacent portion of Mt. Desert about the Sea Wall 

 there exist some remarkable differences in the flora, as 

 well as some strong points of union. Under almost pre- 

 cisely the same conditions, we find Corema near the Sea 

 Wall, but not on the Cranberry Isles ; we find Montia, 

 Stellaria humifusa, and Rubus Chamcemorus on the Cran- 

 berry Isles, but not on Mt. Desert ; we find Symplocarpus 

 foetidus and Hippuris vulgaris on the Cranberry Isles and 

 also on Mt. Desert, but at the Sea Wall alone. Such 

 evidence as this may point to the introduction of certain 

 plants on Mt. Desert by way of the Cranberry Isles, while 

 on the other hand doubtless most of the plants of the 

 Cranberry Isles came from Mt. Desert. 



It is certainly far from improbable that the more 

 northern plants came to the Cranberry Isles by sea, either 

 from the north in later times, or from the south when 

 these islands first appeared above the sea at the conclusion 

 of the glacial period. If from the north, there would be 

 little opportunity for colonization on the rocky eastern and 



