196 THE AMERICAN MIDLAND NATURALIST 



The Invasion of a Missouri River Alluvial Flood Plain. 



BY HERBERT C. HANSON. 



INTRODUCTION 



An interesting invasion of an alluvial bank, formed in the spring 

 of 1916 by the Missouri river, near Peru, Nebraska, was studied 

 during August and September, 1916. The vegetation on new land 

 formed by river or lake activity has been the theme of several writers 

 and is summarized by Clements (2). The plants mentioned in this 

 article were named according to the second edition of Britton and 

 Brown's Illustrated Flora. The identification of difficult species 

 was verified by comparison with preserved specimens in the her- 

 barium of the University of Nebraska. 



DESCRIPTION OF THE ALLUVIAL BANK 



The Missouri river, colored yellow by the enormous load of 

 fine soil carried in suspension, overflows its banks every spring. 

 As the flood recedes great quantities of silt, clay and sand, besides 

 trees, logs, brush and herbaceous plants are deposited on the flood 

 plain. An area, about half a mile long and varying in width from 

 about fifty feet to several hundred feet, forming the bank on the 

 Nebraska side of the river, was denuded of vegetation by the spring 

 flood of 1 9 16. Most of the area was approximately flat, in some 

 places sloping gently to the river's edge, in other places forming a 

 vertical bank of three to five feet. 



The soil was very, fine, composed of a mixture of fine sand, silt 

 and clay. Frequently, scales formed on the surface and cracks from 

 six inches to thirty inches deep, and up to six inches wide, formed 

 in the more clayey soil. 



THE INVASION 



I — BRUSH PILES 



Logs, brush and other debris were scattered over the bank 



after the water had receded. Fruits, seeds, roots, rootstocks, stems, 



and, in places, entire plants were held by the brush, giving rise to 



clumps of vegetation. 



Equisetwn was usually restricted to these brush piles, growing 

 from rootstocks. Willows, growing from roots and slurs, were 

 also common. Other plants found growing in the brush were 



