GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 545 



northern forest. Among the predominant trees are various Oaks, 

 several Elms, Maples, Beech, Walnut, Hickories, Gums (Liquidambar 

 and Js"yssa), Ashes, Tulip-tree, Sycamore (Platanus), Poplar. Far- 

 ther south appear the Magnolias, Persimmons, Papaw (Asimina), and 

 some other southern types, which increase as the Gulf of Mexico is 

 approached. These trees are, with few exceptions, deciduous, and 

 in the spring the floor of the forest is carpeted with many beautiful 

 flowers, which pass through their whole growing period in a few 

 weeks. Of the early flowers especially characteristic of the Ameri- 

 can forest may be mentioned species of Claytonia, Dicentra, Erigenia, 

 Sanguinaria, Erythronium, Trillium, Podophyllum, and Jeffersonia, 

 which are associated with Hepaticas, Anemones, and Violets, much 

 like those of the European woods. 



The deciduous forest is much richer in undershrubs and climbers 

 than the northern forest, and the number of these increases rapidly 

 as we proceed southward, where many beautiful flowering shrubs like 

 the Kalmias, Azaleas, Rhododendrons, Stuartias, Philadelphus, Hy- 

 drangea, etc., give an added charm to the woods. In these southern 

 forests, also, the number of climbing plants increases, and gives 

 a suggestion of the lianas of the Tropics. Clematis, Bittersweet, 

 gigantic Grapevines, Ampelopsis, Trumpet-creeper, Wistaria, and 

 other woody creepers cover the trunks of the trees with their gar- 

 lands of leaves, or clusters of showy flowers. 



Autumn gives an additional beauty to these great deciduous forests, 

 when the Maples, Gums, and other trees display the magnificent colors 

 of their ripening foliage. 



Near the coast, and farther inland southward, are barren sandy 

 districts, " Pine barrens," which are occupied almost exclusively by 

 Pines (P. palustris, P. tceda, etc.), but these cover a relatively small 

 area compared to the great deciduous forests. 



Finally, in the extreme south of Florida is a small district where 

 the forest is almost tropical in its composition, and contains a num- 

 ber of forms related to the adjacent West Indian types. Palmettoes, 

 wild Figs, a few epiphytic Orchids and Tillandsias, recall faintly the 

 exuberant growth of these plants in the neighboring islands of Cuba 

 and Jamaica. 



Prairies. With the diminishing rainfall westward, the forests of the 

 Atlantic states gradually give way to the prairies which cover most of 

 the region between the Mississippi and the base of the Rockies. The 

 transition is not a sudden one, and in southwestern Michigan, western 

 Indiana, and Illinois patches of prairie occur in the forested area, or 

 groves of trees occur scattered over the prairie region. The " Oak 

 openings " of this region are of this nature. They consist of groves 

 of somewhat scattered trees, mostly Oaks of several species, with 

 little or no undergrowth of shrubs. Even these disappear as the 



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