INVASION OF A MISSOURI RIVER ALLUVIAL FLOOD PLAIN 197 



Cyperus erythrorhizos , Persicaria lapathifolia, Bidens frondosa, B. 

 cernua, Xanihinm commune, Panicum dichotomiflorum, Chaetochloa 

 glauca, Scirpus validus, Acnida tuber culata, and Echinochloa crus- 

 galli. 



2. — -WATER LEVEL ZONES 



Figure 3 illustrates how sticks and other brush were deposited 

 on the shore just beyond the reach of the waves. 



The seeds and fruits caught in the brush were so abundant 

 that they could be gathered by the handful. As the flood water 

 receded new water levels were formed. The duration of the water 

 at a certain level determined, largely, the amount of brush and seeds 

 deposited at that level. The number of seeds deposited determined 

 the width and the density of the vegetative zone formed from the 

 germination and growth of the seeds at the water level. This 

 accounts for the variation in the number of plants in the various 

 zones as shown in figure 4. 



The number of vegetative zones on the area varied according 

 to the degree of slope. Where the slope was gradual, as in figure 4, 

 as high as 15 zones were found; but where the slope was vertical 

 no zones were found. The most abundant plant in these zones was 

 Cyperus erythrorhizos. The brown color of this species caused the 

 zones to form a striking contract with the light gray of the soil. 

 Bidens frondosa and B. cernua. were also abundant. The following 

 plants occurred frequently; Radiada palustris, Verbesina alba, 

 Strophostyles hehola, Salix interior, S. cordata, Persicaria pennsyl- 

 vanicum and Potentilla paradoxa. 



3. — LEVEL AREAS. 



The vegetation of the level areas varied considerably. In 

 some places seedling willows and poplars were abundant, and 

 various grasses and herbs occurred sparingly among them. In 

 other places willows, grasses and herbs, but no poplar, were found. 



In other places only herbs and grasses were growing. (Fig. 1.) 

 The absence of willows or poplars on certain areas is due to the fact 

 that these areas were still covered by water when the seeds of these 

 trees were migrating. On the more sandy areas were found usually: 

 Eragrostis hypnoides, E. purshii, and Panicum capillar e. Other 

 plants occurring on the leves areas were Cyperus erythrorhizos, 

 Bidens cernua, B. frondosa, Radicula palustris, Panicum dichotomi- 

 florum, Rumex crispus, Persicaria lapathifolia, P. Pennsylvania, 



