Climate of Middle Illinois. 9 



liiore or less the same flora, with peculiar coniferse and trees with 

 deciduous leaves; southward, increasing in number of species and pass- 

 ing over into the Calif ornian province. A Province of Mixed Forests: 

 Coniferse and leaved-woods, occupying the tract of land from Lake Win- 

 nipeg and the great lakes to Nova Scotia and New Jersey; and, southward, 

 in the AUeghanies to Georgia. This should be divided in three districts: 

 (a) Around the great lakes (Canadian) conifeee prevailing; (h) coast from 

 Nova Scotia to Delaware, North Atlantic, deciduous trees prevailing; (c) 

 AUeghanies, coniferae, with many Ericaceae and some Magnoliaceae. A Pro- 

 vince of Deciduous-leaved Trees with two districts: (a) The Ohio Valley, 

 with nearly exclusively deciduous-leaved trees; (h) the Upper Mississippi, 

 with deciduous-leaved trees and prairies, the former, westward, decreasing in 

 number of species. A Province of Evergreen-leaved Trees, between the 

 Atlantic coast from Virginia to North Florida, and along the Gulf of 

 Mexico to the Brazos, in Texas. This could be divided in an eastern and 

 western district, but the number of species, common to both, is so great, 

 and the character of the landscape so similar, that it is not advisable. The 

 area is coincident with that of the tertiary formation. 



3. The California Flora, from San Diego to the Columbia River, and 

 west of the Sierra Nevada. These mountains, as well as the coasb range, 

 are covered with many peculiar species of coniferae. The valley of the 

 Sacramento and San Joaquin is sparsely wooded mostly with oaks, among 

 which are several perennial-leaved species. In the coast range, north of 

 San Francisco, the thick forest does consist mostly of the same species in 

 one locality, and of another in the next a. s. o. Southward of San Fran- 

 cisco the forests grow thinner and thinner, with only a few coniferae, and 

 at Santa Barbara the mountains are nearly bare or covered with low shrubs. 

 There is the transition to the North Mexican Flora. 



4. The region of the prairies is characterized by a dry atmosphere, 

 little precipitation and partly absence of any tree-growth. 



The northern part, known as the plains (54° — 38° north latitude), 

 is divided from north to south by the Rocky Mountains, and has on both 

 sides the same flora, crossing the lower parts of the mountain-range. 

 Amongst the characteristic plants are the most common several species of 

 Artemesia, known under the name " Sage. 



The southern part, comprising Arizona, southeast California, the 

 southern parts of Nevada and Utah, New Mexico, West Texas and North 

 Mexico is characterized by many species of Cactaceae, and thorny, woody 

 plants, mostly small trees. There are many peculiar Compositae of which, 

 out of two hundred and twenty-one North American genera, one hundred 

 and sixty-five are represented in this province; and of these again seventy- 

 one do not extend to California and to the East neither. Out of fifteen 

 hundred and thirty-five North American species of this order seven hun- 

 dred and forty-four we find there, and of those five hundred and forty-two 

 only in this province, although many of them in tropic America. 



