551 THE SCIENTIFIC MONTHLY 



plants, many of which were of southern affinities. Many southern 

 species still reach their extreme northern outposts of distribution in 

 this region. Most of the southern species are found on the coastal 

 plain, but a few have spread north and west of it. At the present time 

 over 13 per cent, of our local plants reach their northern limits within 

 one hundred miles of the City of New York. Many other southern 

 plants, also, range only slightly to the north of us. 



About 8 per cent, of the native vegetation, also, consists of north- 

 em species that reach their southern limits within the local flora area, 

 and many more are found to the south of us in the mountains. The 

 great range of hills, stretching northeast-southwest from the Berk- 

 shires through the Catskills and the Highlands of the Hudson in New 

 York, the Kitta tinny in New Jersey and to the Blue Mountains of east- 

 ern Pennsylvania, serve literally as a broad highway down which a host 

 of northern species are scattered, and to the seaward of which certain 

 kinds have never been known to go. That other great group of species 

 that creeps, almost insidiously, from the south, seems perforce to have 

 been huddled between the mountains and the sea. The transition be- 

 tween these northern and southern elements of our flora is, of course, 

 nothing like so sharp as the geological regions they generally occupy 

 would seem to indicate. Many sporadic marauders have spread from 

 both camps, apparently far out of their element. Sometimes these 

 lonely outposts survive the competition of the new environment ; that is 

 notably the case of the hemlock in southern New Jersey, far from its 

 usual rocky hillsides, and of the coast white-cedar {Gliammcypans) 

 which flourishes in the coastal-plain bogs, and maintains a rather 

 splendid isolation at Greenwood Lake, in northern New Jersey. Scores 

 of these cases could be cited illustrating the main lines of the distribu- 

 tion of our flora by occasional aggressive exceptions to it. Such spo- 

 radic occurrences form one of the most fascinating chapters in the his- 

 tory of our native flora, for are they not militant outposts of a mighty 

 horde of conservatives? Sometimes they perish miserably as the little 

 twin-flower has long since done on southern Long Island, miles from 

 its mountain home. Of the number of such tragedies no man can even 

 guess, still less speculate as to their causes, but speculation could weave 

 about such occurrences, and they are very numerous even in such a 

 limited area as this, a story the significance of which has breath-taking 

 possibilities. For with these outcasts, whether living or dead, is bound 

 up a whole history of changing climates and shifting levels of our con- 

 tinent — mighty forces which have scattered here and there mute little 

 relics of their sport. 



The real potency of these geological forces, or historical factors of 

 distribution, is so great and its appeal to the imagination can be made 

 so alluring, that we are in danger of attributing the general complexion 

 of our vegetation almost solely to them. Nothing could give us such a 



