82 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



than their southern Hmits. The shade and consequent coolness 

 are mostly caused by the dominant Chamaecyparis, and the 

 slightly less common Acer carolmianum and Nyssa, all of which 

 are here near their northern limits, two of them being known only 

 from Maine, the other from southern Massachusetts, southward. 



An analysis of the woody undergrowth shows the same char- 

 acteristic. Seventy-six per cent of the shrubs and vines at the 

 Merrick swamp are of southern rather than northern afhnities. 

 Similar figures for the cedar swamps in Connecticut (22) show 

 68 per cent of the woody plants as southern and in the pine-barrens 

 yy per cent (19). How accurately these figures represent the 

 dropping out of southern woody species as we come northward 

 no one can say, but at least they indicate the general tendency of 

 the white cedar to be associated with typically southern woody 

 plants and to lose some of these, but not many, as it occurs 

 northward. We have then a cool, almost coniferous-bog condi- 

 tion of the north, on a hot coastal plain, caused mostly by southern 

 trees and shrubs, all of which are much nearer their northern edges 

 of distribution than their southern. 



This raises at once the question as to what is the character of 

 the herbaceous vegetation occurring in the swamp. An analysis 

 of the above list shows that yy per cent of the herbaceous vege- 

 tation is northern rather than southern. Similar figures from 

 Connecticut show about 70 per cent of northern herbs. We have 

 in this a really remarkable condition, some of which may be due 

 to historical factors. Here, in a locally cool region, we find 

 an aggregation of northern herbs vastly in excess of the percentage 

 of such herbs in the surrounding region and their occurrence 

 conditioned by the shade provided by jiredominately southern 

 woody plants. 



The mixture of these northern and southern elements in one 

 swamp, which is, as shown above, not peculiar in this respect, 

 is an excellent, if rather concentrated example of the distribution 

 of the Long Island flora generally. The great majority of species 

 on the coastal plain are southern, many of them reaching their 

 northern distribution outposts on the island. Along the morainal 

 ridge and north of it, however, the species are more northern in 

 character. More or less of a tension zone exists between these 

 two elements. P)iit in this cedar swamp there is no evidence of a 



