18G MISSOURI BOTANICAL GARDEN. 



While the bottoms on the north side are covered chiefly by 

 grasses, trees and shrubs form the most striking feature of 

 the bottoms on the south side- The lower terrace is occupied 

 in part by willows, Salix cordata X sericea, S. longifolia, S. 

 nigra and S. sericeaj and by Forestiera acuminata. Among 

 the larger herbs Vernonia novehoracensis is most prominent, 

 Chacrophyllum procumhens and Scnedo aureus are striking 

 features of the spring flora. This lower terrace has partly 

 been invaded by the more common roadside weeds, such as 

 Arctium Lappa minus. Species of Verbena arc common. 

 There are a few trees of Ulnms amcricana and Gleditschia 

 triacanthos. Forestiei^a acuminata forms large clumps. The 

 higher terraces are occupied by Ulmus fulva and oaks, chiefly 

 Quercus bicolor, Q. macrocarpa and Q. palustriSj by walnuts, 

 Juglans cinerea and J. nigra, and by hickories, mainly Carya 

 amara. Here occur two specimens of 0. olivaeformis, the only 

 representatives in our section on the Missouri side. Several 

 species of Crataegus are found here. 

 In connection with the wet bottoms must be mentioned 



F 



the great similarity of the flora of these regions to that of 

 the swamps on the plateau, where the most striking features 

 are willows and Iris versicolor (plate 14). 



THE RIVER.* 



The Missouri Shore. 



On the Missouri side of the Mississippi, the river shore may 

 be divided into three zones, which, in the earlier part of the 

 year, ordinarily are submerged, appearing in summer and au- 

 tumn only. The first zone, immediately adjoining the water, 

 is from two to four yards wide and is composed of the St. 

 Louis limestone, not covered by mud. Probably the constant 

 change of level of the river, varying within a few feet, is suffi- 

 cient to prevent the accumulation of any deposit. There is 

 no vegetation unless of a transient nature and limited to algae 

 left behind by the waters of the river in the small shallow 

 pools, seldom more than one foot in diameter. In the second 

 zone, with a width of from five to ten yards, the stones are 



* The plankton of the Mississippi has been omitted from this study. 



s. 



