34 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Vol.Yl. 



to the Pacific flora. UTegundO) which is hardly distinct from Acer, has 

 an Atlantic specie- extending to and through the Rocky Mountains; a 

 id hut closely related species takes its place in California. Staphy- 

 Irtt. which affects only forest regions, has an Atlantic and a (local) Pacific 

 species. Glossopetalon is peculiar to the intermediate dry region ; the. 

 original species occurs on and beyond the southern borders of the 

 Great Basin ; a second one is on its northwestern border. Ungnadia of 

 Texas is rather too tar southwest to be well reckoned in the Atlantic 

 forest flora, yet it belongs to it. 



An A< akdiackj:. — Represented by the genus Rhus. The only species 

 which extends across the continent is R. aromatica, in a peculiar western 

 variety. 7/. glabra, the low Sumach, extends to and beyond the Eocky 

 mountains. The common Sumach, the Poison Dogwood, and some others 

 are wholly eastern, while Rhus Toxicodendron reaches the Eocky Mount- 

 ains : on the Pacific side it is replaced by an equally poisonous and very 

 similar species. Southern California has two other species of South 

 American type. 



LEGUMiNOSiE. — This being one of the very largest orders in most 

 parts of the world, only characteristic features can be noted. The At- 

 lantic flora is rich in genera, but poor, comparatively, in species ; the 

 Pacific is very poor in genera, but several of the genera are very numer- 

 ous in species. The intervening region on the western side has the Cal- 

 ifornian character. They may be referred to under the suborders. 



1 *A pilionace^e. — The great preponderance of Pacific species is attrib- 

 utable mainly to the great development of four genera, viz: Astragalus, 

 Lwpinus, Trifolium, and Hosackia. The latter is the only purely Ameri- 

 can type of the four, though very near to the Old World genus Lotus, 

 and. but for one species which has nearly reached the Atlantic seaboard, 

 WOUld be wholly western. 



The only peculiar Pacific genus is Pickeringia, of a single species. 

 There is no peculiar genus of the Eocky Mountain flora, Olneya being 

 Arizonian. The exuberance of Atlantic genera is largely due to genera 

 which are divided between the Eastern United States and Eastern 

 A>ia. such 'as WistaHa, Apt08, .1 mphicarpivn, Lespedeza, Cladrastis. and 

 to some exclusive genera, such as Bapiisia, Robinia, Petalostemon ; 

 also to the absence toward the Pacific of genera which the Atlantic 

 States share with Mexico and South America, such as Tephrosia, Indigo- 

 /era, Sesbania, 8tylosanthes ) Desmodium (the Largest Atlantic States 

 genus), f'ri/ihriiKi. Clitoria, Centrosema, Galactia, Ehynchosia. More- 

 over, the botanj of California should surrender its eleven species of 

 Dalea, since they all properly belong to the Arizonian and Great Basin 

 floras rather than to that of the Pacific region. It is a characteristic 

 genus of the Mexican plateau and of its extension northward. Astra- 

 galut, feebly represented in the Atlantic States, and its appendage, 

 Oxytropis, have their American headquarters in the plains and mount- 

 ains of our interior region, under conditions not unlike those of Northern 



