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 

 frutescent, but by no arborescent, species : 



Euonymus. Ainelanchier. Vaccinum. Rhododendron. 



Rhus. Viburnum. Kalmia. Forestiera. 



Cercis. 



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

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

 Pacific region. Rhamnus, jEsculus, Acer, Nee/undo, Primus, Pyrus, Cratcegus, Gornus, Sambuous, Fraxinus, Platamts 

 Myrica, Qucrcus, Betula, Alnus, Salix, Populus, Thuya, Cltamwcyparis, Juniperus, Taxus, Torrcya, Pinus, Picea, Tsuga, 

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



Ungnadia, Eyscnhardtia, ParMnsonia, Prosopis, Acacia, Chilopsis, and Yucca, genera of the Mexican flora, are 

 common to the two regions. 



Arbutus, a genus of the Pacific region, jiist 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. Heterorueles. Libocedrus. Pseudotsnga. 



Olneya. UnYbellularia. Cupressus. Wasliingtonia. 

 Vauquelinia. 



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

 Ceanothus. 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. "Eysenliardtia. *Parkiusonia. Vauquelinia. Wasliingtonia. 



*Ungna3ia. Dalea. Leucama. Cereus. 



Porliera and Leuccena belong to the Atlantic; Canotia, Dalea, Olneya, Vauquelinia, Cereus, and Wasliingtonia 

 to the Pacific region. 



DISTEIBUTION 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; they are principally confined to the subarctic Northern Forest and to the narrow belt along the southern 

 boundary of the United States. 



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



Prosopisjuliflora. Sarnbucus Mexicana. Salix longifolia. Populus balsamifera. Picea alba. 



Pyrus saiubucifolia. Betula papyrifera. Popnlus tremuloides. Juniperns Virginiaua. Yucca baocata. 



Prosopis juliflora, Sambucus Mexicana, and Yucca baccata belong to the Mexi-jan flora of the south; Salix 

 lonyifolia 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 sambncifolia, 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 aceroidcs. Crataegus tomentosa. Quercns Etnoryi. 



Coudalia obovata. Parkinsonia aculeata. Fruxinus viridis. Alnus incana. 



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



Ungnadia speciosa. Prunus Penusylvanica. 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, Parldnsonia aculeata, 

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

 Sapindus marginatus, of the southern Atlantic region, extends through western Texas to the Pacific-Mexican 

 region. Prunus Americana, Prunus Pennsylvania, 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, Cratatgus tomentosa, Fraxinus viridis, and Celtis occidentalis are widely distributed through 

 the interior Pacific region, although nowhere reaching the coast. 



