680 GEOGEAPHICAL AND GEOLOGICAL BOTANY. 



Banksiana, P. variabilis, P. rigida, P. serotina, P. pungens, Abies bal- 

 samea, A. taxifolia, A. canadensis, A. nigra, A. rubra, A. alba, Larix pen- 

 dula, L. macrocarpa, Thuja occidentalis, T. sphaeroidea, Juniperus virgi- 

 niana, J. Sabina, Taxus canadensis, Quercus, 25 sp., Fagus sylvatica, F. 

 ferruginea, Castanea americana, C. pumila, Ostrya virginica, Carpinua 

 americana, Corylus americana, C. rostrata, Alnus glutinosa, A. crispa, 

 A. serratula, Betula nigra, B. papyracea, &c., Salix, 27 sp., Populus bal- 

 aamifera, P. monilifera, &c., Myrica cerifera, &c., Platanus occidentalis, 

 Liquidambar styraciflua, Juglans nigra, J. cinerea, &c., Ulmus americana, 

 &c., Nyssa aquatica, Fraxinus alba, F. nigra, &c., Ornus americana, Kibes 

 floriduni, R. aureum, &c., Vaccinium, 20 sp., Andromeda, 10 sp., Kalmia 

 latifolia, K. angustifolia, K. glauca, Azalea viscosa, A. nitida, A. glauca, 

 A. nudiflora, &c., Rhododendron maximum, Gornus florida, C. alba, C. ca- 

 nadensis, &c., Hamamelis virginiensis, Spiraaa salicifolia, S. chamsedri- 

 folia, S. opulifolia, S. hypericifolia, &c., Gillenia trifoliata, Cratsegus, sp., 

 Cerasus pumila, C. nigra, &c., Purshia tridentata, Rubus, 20 sp., Pyrus 

 sp., Robinia Pseud-acacia, R. hispida, Gymnocladus canadensis, Rhus 

 typhina, R. glabra, R. venenata, R. toxicodendron, &c., Ptelea trifoliata, 

 Ceanothus americanus, &c., Rhamnus alnifolius. &c., Ilex opaca, &c., 

 Euonymus americanus, E. atropurpureus, Staphylea trifolia, Ampelopsis 

 hederacea, Acer rubruni, A. dasycarpum, A. saccharinum, A. striatum, 

 Negundo fraxinifolium, Xantboxylum fraxineum, X. tricarpum, Tilia gla- 

 bra, T. pubescens, Liriodendron tulipifera. 



In the northern parts (to 50-55 N. L.) no cultivation. South of this 

 the same plants as those cultivated in the second region, but Maize more 

 extensively. The Californian climate is very uniform, the resting period 

 of vegetation occurring in the dry summer, "vines, Olives, Maize, Oranges, 

 and Iruit-trees of all kinds nourish here as well as Wheat, whilst the 

 loftiest forest trees, the Sequoias, grow here as once they did in Britain. 



The Prairie Region corresponds to the Steppe Region of Central Asia. 

 Extremes of temperature and great drought are the characteristics of this 

 region; salt plains exercise a marked influence on the vegetation, but 

 where irrigation is practicable the country becomes very fertile. 



The evidences of climatic changes in past eras of the existing flora of 

 the continent, says Hooker, are seen in the prevalence of arctic and 

 northern species of plants in the alpine zones of the meridional mountain- 

 chains, the Appalachian, Rocky Mountains, and Sierra Nevada, even as 

 far south as the 33rd parallel. These plants had spread southwards 

 during a period of cold, and on its subsequent mitigation had retired to 

 the lofty situations they now inhabit. To the former existence of a 

 warmer climate we may partly look for the extension of Mexican types 

 to the dry regions west of the Rocky Mountains up to the 41st parallel ; 

 and to it may be attributed the remarkable northward extension of the 

 Cacti in a very narrow meridional belt, scarcely 100 miles broad, along 

 the eastern flanks of the same mountains, from their headquarters in New 

 Mexico, in the 33rd, almost to the 50th parallel. 



(See Gray's ' Botany of the Northern United States,' and numerous 

 publications of the American botanists on the Flora of their continent. 

 Sir W. Hooker's Flora Boreali-Americana ' should also be consulted.) 



