Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 295 



meadow forms, thus in dense association completely dominating 

 wide expanses that are otherwise in reality of the wet meadow 

 type. The most of the characteristic wet meadow species are lack- 

 ing in these areas however. 



Composition of the Water Hemlock Association 



dominant species 



Asclepias incarnata Phalaris arundinacea 



Cicuta occidentalis Scirpus atrovirens 



ASSOCIATED SPECIES OF LESS ABUNDANCE 



Agrostis Jiyemalis Mimulus jamesii 



Berula erecta Scirpus americanus 



Ciciita hulhifera Scutellaria galericulata 



Halerpestes cymbalaria Spartina cynosuroides 



Hordeum jubatum Stachys palustris 



Lythrum alatiim Teucrium occidentale 



The close relationship between this and the last association is 

 seen from a comparison of species lists from the two. The above 

 enumerated species are those that are most common in this associa- 

 tion and they are all found in the previous association, but as a rule 

 in greater abundance in the present association. 



This association is a noteworthy feature in the associational 

 contrast of the lowlands during late July when the water hemlock is 

 in bloom. The tall, scantily leaved, slender stems with their numer- 

 ous, large, convex umbels of white flowers constitute, with the darker 

 greens, a background against which the rose-colored flower clusters 

 of Asclepias incarnata contrast remarkably. 



Although the usual relation is more clearly with the . wet 

 meadow association, the presence of members of the marsh series in 

 the lower situations indicates a rank about parallel with the rush- 

 sedge wet meadow association. So also in the drier sites certain 

 typical meadow plants are found invading the water hemlock areas, 

 and here the association bears an unmistakable close relationship to 

 the hay meadow association to be discussed in the following pages. 

 The hemlock is frequently seen as relicts in lower portions of the hay 

 meadows. It seems therefore in general that this association is a 

 hydro-mesophilous one with a more decided tendency toward meso- 

 phytism than the previous association, and that it should be linked 



