PLANT ASSOCIATIONS OF ALABAMA. 37 



undershrubs (including the low perennials with a woody stem and 

 branchlets partially dying at the close of the season of growth) and 

 perennial, biennial, and annual herbs. 



HYDROPHYTIC PLANT ASSOCIATIONS. 



Of the associations of this group the following are recognized in 

 the Alabama flora, consisting of plants: (a) Floating free in water either 

 on the surface or submerged; for example, the water fern (Azolla), 

 duckweeds (Lemna, Spirodela), bladder worts (Utricularia), horn weed 

 (Ceratophyllum), etc. ; (b) connected with the soil, rooting either on 

 rocks, as Podostemon, many fresh- water algae, and some mosses (Lith- 

 ophile associations), or in the loose soil, as the pondweeds (Potamo- 

 geton), ditch weed (Ruppia), eelgrass (Vallisneria), and of the higher 

 cryptogams Nitella. 



(c) Immersed only at their base and rooting in the slightly sub- 

 merged or swampy soil, forming associations of paludial plants, as the 

 vegetation of the grassy marshes and of bogs, and the shrubs and trees 

 covering the alluvial swamps; for example, cypress swamps. 



XEROPHYTIC PLANT ASSOCIATIONS. 



These consist of the vegetation of the dry, exposed, drifting sands 

 of the seashore and of dunes, and the woody vegetation of loose sands 

 (Psammophile associations); also of the vegetation of dry prairies 

 ("bald prairies"), and of the forests of the dry uplands, either of 

 evergreen cone-bearing trees (pine barrens) or deciduous trees. 



HALOPHYTIC PLANT ASSOCIATIONS. 



These are composed mostly of aquatic plants, inhabiting the beach 

 and saline marshes of the seashore. 



MESOPHYTIC PLANT ASSOCIATIONS. 



These embrace the plant associations confined to a soil and atmos- 

 phere of moderate humidity, as grassy swales, canebrakes, the arbo- 

 real vegetation of the subtropical forests of broad-leaved evergreen 

 trees and shrubs, and the deciduous forest of the lowland with a fresh 

 soil rich in humus, never or infrequently overflowed. 



GENERAL CHARACTER OF THE ALABAMA FLORA. 



The flora of Alabama stands in the number of species and varietal 

 forms, as well as in the diversity of their characteristic associations, 

 unsurpassed among those of adjoining regions. This wealth and vari- 

 ety of Alabama's plant life is easily explained when, on the one hand, 

 its area is considered, extending over nearly 5 degrees of latitude, and on 

 the other, the diversity of its topographical features, varying from the 



