320 Part III. Chapter 4. 
To be considered in connection with this second category of species is a 
very significant group of genera which are represented in eastern North America 
by two closely allied species, one in the coastal plain, the other in the 
Appalachian region. With the exception of Clethra (which is largely tropie) 7 
all these genera, like many of those represented by species of the second B 
category, have their present center of distribution inthe warmer part ofthe 
north temperate zone. This may also be said of the larger groups to 
which many of them belong, e. g. the families Calycanthaceae, Sarraceniaceae, 
Hamamelidaceae and Monotropaceae and the tribes Hydrangeae of Saxi- 
fragaceae and Andromedeae of Ericaceae. Some of them are known to 
belong to floral types which were very widely distributed in the northern 
hemisphere during the early part of the Tertiary, in not a few cases ranging 
as far north, as Greenland and Alaska. Several of these genera, broady 
speaking, appear to be on the wane, as distinguished from the dominant nd 
aggressive types of presumably neotropic origin to which species of the first 
category chiefly belong. The following list, according to KEARNEY, includes 
some ofthe plants which are represented by the same or closely related species 
found in the Appalachian region and also in the coastal plain, viz. \ 
Genus Coastal Plain Species | Appalachian Species 3 
Calycanthus (Butneria) florida L. glauca Willd. (= fertilis 
Walt. 
Sarracenia flava L. flava var. oreophila 
Philadelphus grandiflorus Willd. inodorus L. 
Hydrangea quercifolia Bartr. ... er 
cinerea Small 
Fothergilla Gardeni Murr. (= caro- | arborescens L. 
lina L.) 
Stuartia 'virginica Cav. (= Mala- | major Lodd. 
codendron L.) 
Schweinitzia (Mono- Reynoldsiae Gray odorata EIl. 
tropsis) 
mar axillaris D. Don. acuminata D. Don. 
racemosa Gray. Catesbaei Gray. : 
Andromeda (Pieris) phillyreifolia Hook. tloribunda Pursh. 2 
Halesia (Mohrodendron) | diptera L. 
carolina L. (= tetrap- 
parviflora Michx. | 
tera L.) 
5. Relationship in Western North American Flora. 
Rocky Mountain Flora; its Affinities. The Rocky Mountain Region may for 
the purposes of our comparison be divided vertically into three belts: 
ı. An alpine treeless belt above the belt where trees grow. | 
2. A wooded belt, in some places covering, in others locally adorning, the : 
mountain slopes. | . 
