278 



are coated with a dense mat of exposed rhizomes of Juncus. At "C" 

 in the figure is a Juncus dune in one of the stages of obHteration. 



The flora of these interesting- rehcs is very uniform. Juncus bal- 

 ticns littoralis is the characteristic species and occupies 95 to 99 

 per cent, of the area of the caps in Figure i, Plate XLVI. The fol- 

 lowing are infrequent in their occurrence and irregular in their dis- 

 tribution: evening primrose {Oenothera rJiouibipetala), Russian 

 thistle (Salsola kali tenuifolia), sandbur (Cenchrus carolinianus) , 

 silverweed (Pofentilla anserina), Sporobolus cryptandrus, dogwood 

 (Cornus stolonifcra), and Calauiovilfa longifolia. 



Proceeding southward from the portion shown in Figure i, Plate 

 XLVI, the shore-line begins to curve somewhat to the west and is not 

 subject to so much wave action. The rifts in the Juncus association 

 become less frequent and of less and less importance as the shore dips 

 away from the direct attack of the waves. The sand is piled at the 

 base of the Juncus rhiaoines so that the bluff is concave. The associa- 

 tion still contains over 90 per cent, of Juncus balticus littoralis, but 

 secondary species are a httle commoner and more sandbur (Cenchrus 

 carolinianus), Cornus stolonifcra, Ptelea trifolia, Canada thistle (Cir- 

 simn arvense), Oenothera rhonibipetola, and balm of Gilead (Popu- 

 lits candicans) are present. 



Besides characterizing an association, Juncus balticus littoralis 

 grows in a majority of the other associations of the Beach region. 

 It will be given consideration accordingly under them. Notwith- 

 standing its apparent disregard for haljitat it rarely shows any 

 modifications in form in the habitats in which it is evidently a relic. 



THE POTENTILLA ANSERINA ASSOCIATION 



From the Juncus balticus littoralis association the sand slopes up 

 gradually to the Sali.i- syrticola or fringing-dune association. This 

 slope is characterized by a rather dense growth of low plants of which 

 silverweed ( PotentUla anseri)ui) constitutes from 70 to 90 per cent. 

 It may be termed a tension-line association, and separates very dis- 

 tinctly the fringing dune from the Juncus association. PotentUla an- 

 serina grows in each of the three associations, but it shows its max- 

 imum development in the PotentUla' association. In the bordering 

 associations the size of the individuals varies to a minimum and their 

 number to zero. 



PotentUla anserina spreads very rapidly by means of runners 

 which radiate from the parent plants. At quite regular intervals 

 of from one to two decimeters each runner sends out roots and leaves. 



