Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 283 



pure, alternating- stands, as well as frequently in mixture, covering 

 great stretches about the lakes and in old lake beds with a dense 

 jungle of closely aggregated stems. 



Composition of the Bulrush-Reed-Grass Association 

 dominant species 

 Phragmites phragmites Typha latifolia 



Scirpus americanus Zisania aquatica 



Scirpus validus 



PRINCIPAL AND SECONDARY SPECIES 



Alisma plantago-aquatica Polygonum harhvrightii 



Asclepias incarnata^ Potamogeton lonchites^ 



Berula erecta Potamogeton natans^ 



Ceratophyllum demersuw?- Rumex britannica 



Cicuta occidentalism Sagittaria arifolia 



Eleocharis acicularis Sagittaria latifolia 



Eleocharis palustris Scirpus Uuviatilis 



Myriophylluni/ spicatuw} Scirpus pallidus 



Nymphaea advena^ Spartina cynosuroides 



Phalaris arundinacea ' Stachys palustris^ 



Polygonum amphibium^ Teucrium occidentale^ 



Polygonum emersum Typha latifolia 



1 Relicts. 2 Invaders. 



Scirpus validus is by far the most frequent of the bulrush-reed- 

 grass dominants. This species is found in great abundance in every 

 lake and marsh region of the sandhills as well as in smaller local 

 spots along the streams of the region. The bulrush is found in 

 deeper, more open water than any of the other species. The reed- 

 grass is no less abundant but its frequency is much less than that 

 of the bulrush and it is not found in such large stands as the latter 

 species. The wild rice, Zisania aquatica, and the cat-tail are much 

 less frequent in the sandhills than the two above-mentioned species. 

 Nevertheless one occasionally finds extensive beds of both of the 

 latter. The rice sometimes completely usurps shallow lakes and the 

 tall, light-green, grassy vegetation is especially noteworthy when the 

 large sexually divided panicles are fully developed. Again, when 

 stands of rice, reed-grass, and bulrush alternate, a most conspicuous 

 color differentiation results, grading from yellow-green in the wild 

 rice through darker pea-green in the reed-grass to deep blue-green 

 in the bulrush. 



