12 FOREST TREES OF NORTH AMERICA. 



The following genera of the Atlantic region, 9 in number, are represented in the Pacific flora by one or more 

 fhitescent, but by no arborescent, species : 



Enonymos. Amelanchier. Vaccinam. Rhododendron. 



Rhus. Vibamnni. Kalmia. Forestiera. 



Cercis. 



Ptelia, Condalia, Sapindus, Eobinia, Bumelia, Celtis, Morns, and Juglans, genera reaching their greatest 

 development in North America in the Atlantic region, extend with a single arborescent representative into the 

 Pacific region. Rhamnus, Msculm, Acer, Negtmdo, Prunus, Pyrus, Cratcegus, Cornus, Samhuous, Fraxinus, Platantis^ 

 llyrica, Quercus, Bitula, Alnus, Salix, Populm, Thuya, Ghamcecyparis, Juniperus, Taxus, Torrcya, Pinus, Picea, Tsuga, 

 Abies, and Larix, characteristic North American genera, are widely represented in the two regions. 



Unijnadia, Eysenhardtia, Parkinsonia, Prosopis, Acacia, Chilopsis, and Yucca, genera of the Mexican flora, are 

 common to the two regions. 



Arbutus, a genus of the Pacific region, just reaches, with a doubtful species, the Atlantic region through western 

 Texas. 



The following genera of the Pacific region, 13 in number, have no representatives in the Atlantic region: 



Fremontia. Cercocarpus. * Castanopsis. Sequoia. 



Canotia. Heteromeles. Libocedras. Psendotsaga. 



Olneya. Umbellnlaria. Cupressus. Washingtonia. 



Vauqnelinia. 



The following genera of the Pacific, 3 in number, are represented in the Atlantic region by frntescent species : 

 Ceanothns. Dalea. Cereus. 



The Atlantic forest, exclusive of semi-tropical Florida, contains 45 genera entirely unrepresented in the Pacific 

 region and 7 genera without Pacific arborescent representatives. The Pacific forest contains 13 genera unrepresented 

 in the Atlantic region and 3 genera without Atlantic arborescent representatives. 



The following genera of the Mexican region, 14 in number, are not elsewhere represented in North America. 

 Genera with arborescent representatives in both the Atlantic- and Pacific- Mexican regions are designated by a 

 star () : 



Porliera. Pistacia. Olneya. Acacia. 'Chilopsis. 



Canotia. *Ey8enhardtia. "Parkinsonia. Vanqnelinia. Washingtonia. 



"Ungnadia. Dalea. Leucaena. Cereus. 



Porliera and Leucwnu belong to the Atlantic ; Canotia, Dalea, Olneya, Vauqnelinia, Cereus, and Washingtonia 

 to the Pacific region. 



DISTRIBUTION OF SPECIES. 



In the forests of North America 412 arborescent species have been detected ; of these, 292 species belong to 

 the Atlantic region, and 153 occur within the limits of the Pacific region. Species common to the two regions are 

 rare; tbcy are i)rincipally confined to the subarctic Northern Forest and to the narrow belt along the southera 

 boundary of the United States. 



The following species, 10 in number, cross the continent: 



ProsopiH juliflora. Sambucns Mexicana. Salix longifolia. Populus balsamifera. Picea alba. 



Pyrus sambucifolia. Betula papyrifera. Populus tremuloides. Juniperus Virgiiiiana. Yucca baccata. 



Prosopis juliflora, Sambucns Mexicana, and Yucca baccata belong to the Mexican flora of the south; Salix 

 longifolia also belongs here, although extending northward into the Atlantic and through the Pacific Coast region 

 of the United States. Populus balsamifera, Betula papyrifera, and Picea alba belong to the Northern Forest. 

 Pyrus samhucifolia, Populus tremuloides and Juniperus Virginiana are widely distributed through the central 

 portions of the Atlantic and Pacific regions; they are the only really continental arborescent species. 



The following species of the Atlantic region, 15 in number, extend from the Atlantic into the Pacific region : 



Ptelia trifoliata. Negundo aceroides. Crataegus tomentosa. Quercus Emoryi. 



Condalia obovata. Parkinsonia aculcata. Fraxinus viridis. Alnus incana. 



Sapindus niarginatns. Prunus Americana. Celtis occidentalis. Salix nigra. 



Ungnadia spcciosa. Prunus Pennsylvanica. Morus microphylla. 



Ptelia trifoliata, a widely distributed species of the Atlantic region, extends through western Texas into the 

 extreme southeastern portion of the Pacific region. Condalia obovata, Ungnadia speciosa, Parkinsonia a^uleata, 

 Morus microphylla, and Quercus Emoryi, of the Atlantic-Mexican forest, extend into the Pacific-Mexican region. 

 Sapindus marginatum, of the southern xitlantic region, extends through western Texas to the Pacific-Mexican 

 region. Prunus Americana, Prunus Pennsylvanica, and Alnus incana, widely distributed through the northern 

 portions of the Atlantic region, just reach the eastern limits of the central Pacific region. 



Negundo aceroides, Cratmgus tomentosa, Fraxinus viridis, and Celtis occidentalis are widely distributed through 

 the interior Pacific region, although nowhere reaching the coast. 



