ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 191 



are predominant during the autumn. Where there are wood- 

 lands, Quercus coccinea tinctorial Q. imhricanaj Q. macro- 

 carpa and Q. Muhlenbergii, together with Acer dasycarpum 



and Ulmus fulva, are the species principally encountered. 



The wet bottom. 



This can be compared directly with the similar region on 

 the Missouri side of the Mississippi, though it is much broader, 

 and, like the dry bottom just mentioned, has been converted 

 almost entirely to agricultural purposes. Here and there re- 

 main patches sufficiently large to give an idea of the original 

 flora. This original flora consisted largely of trees and 

 shrubs, the formation being frequently interrupted by sloughs, 

 lakes and swamps. There seem to have been two principal 

 zones. The one, bordering the river and forming a strip of 

 variable width, ordinarily averaging one-half mile, was, and 

 still is, covered by a growth of willows among which Salix 

 longifolia is predominant (plates 11, 16). The remainder of 

 the wet bottom appears to have been covered with woods. 

 These, for the greater part, have yielded to the axe» Por- 

 tions of these woods still remaining will be taken up under 

 a separate heading. 



To a rich spring flora, among which Ranunculaccac such as 

 Isopyrum hiternatum^ Myosurus minimus, Ranunculus abor- 

 tivus and R. ohlongifoKus are the most frequent, with the ex- 

 ception of some Cruciferae, succeeds a luxuriant summer 

 flora, largely consisting of Hypericum mutilum and H. 

 perforatum, Ahutilon Avicennae, Oxalis striata, Amorpha 

 fruticosaj Cassia Chamaecrista, specimens of Baptida leu- 

 cantha in groups of two or three, Potentilla norvegica and P. 

 rivalis millegrana, numerous Compositae, Asclepias incar- 

 nata. Convolvulus Septum , Ipomoea hederacea, L laciinosa, 

 L pandurata and /. purpurea, Stachys polustris. Datura Stra- 

 monium and Z). Tatula, Phytolacca decandra, Polygonum 

 acre, P. hydropiperoides, P. lapathif olium and P. Persicaria, 

 Rumex maritimus and R. crispus, Euphorbia glyptosperma, 

 E. humistrata and Boehmeria cylindrica. A large number 

 of these persist till autumn, the additions at this time being 



mainly limited to the Compositae. Here and there occur 



