34 UNIVERSITY OF MISSOURI STUDIES [l66 



C. Fluviales. Plants of the fluvial zone. 



The fluvial zone consists of the associations peculiar to 

 streams. Excluding the fontinal and the alluvial, there are two 

 fluvial subzones: i. The rival, or stream-bed; 2. The ripa- 

 rian. 



1. Fluviales rivales. Plants of the rival subzone. 

 We have said' that all the streams are devoid of phanero- 

 gamic aquatics. This appears partly due to the rapidity of the 

 streams and to the turbidity of the water, which holds inorganic, 

 rather than organic matter in suspension, but is perhaps chiefly 

 due both to the rocky beds which are in continual process of 

 scouring, and to the fact that all the creeks go dry in large part 

 in times of drouth. There is but one stream-bed association. 



a. Rivales justicioides. The water-willow association 

 consists quite wholly of the water-willow, Jiisticia Americana, or 

 with some admixture of Scirpus Americana, Heleocharis ovata, 

 H. glaucescens, H. palnstris, and Equisetum hiemale next the 

 shore. The stream is often completely choked up with these 

 plants. The favorite haunt is where the stream pours over nar- 

 row ledges, but patches are common in all shallow places. With 

 the Justicia, but next the bank, is usually a line of the shrubby 

 Amorpha fruticosa. The water-cress {Nasturtium offici- 

 nale) similarly chokes up springs at Rocheport. 



2. Fluviales ripariae. Plants of the riparian subzone. The 

 riparian flora accompanies all the streams, but is best de- 

 veloped along those with low banks. Where the banks 

 are rocky and clifif-like, they support mainly a rupestrine flora. 

 The riparian vegetation is marked by a light-green tint which 

 flashes silvery in the wind, the foliage commonly being whit- 

 ened underneath. The riparian flora is partly arboreal, partly 

 arborescent and fruticose, and partly herbaceous. In general 

 the herbs are much less characteristic than the trees and shrubs. 



