Jennings : A Botanical Survey of Presque Isle. 345 



There is here the beginning of the Popuhis-ndge, a narrow lagoon 

 having been formed and filled up, but not till after the cottonwoods 

 had become established. The cottonwoods are now only saplings, 

 but, present conditions continuing, there will develop in time a ridge. 



The At/DHophila-zone. is now on its decline at this place, and in a 

 few years it will likely be supplanted by the Panicum-Artemisia-iox- 

 mation. Such a result will be accelerated by the growth of the Cot- 

 tonwood ridge and the subsequent building up behind it of a more 

 level plain. Associated with the Ammophila here are all the species 

 mentioned for the formation in general, excepting CaJdle and Ett- 

 phorbia. Andropogon, Artemisia and Lathynis are, perhaps, more 

 abundant than the designation, " secondary species, " would indicate. 



The Andropogon Dune-formation. 



In the discussion of the Popitlus dunes or ridges and the formations 

 succeeding the Populus on them, the Andropogon dune-formation was 

 discussed at some length as a component stage of a succession begin- 

 ning with the Popuhis ridge or dune, but, as there are conditions under 

 which the Andropogon dune-formation has no connection with the 

 former, it has been deemed best to accord the Andropogon dune-for- 

 mation a separate treatment. 



The Andropogon is not a strong formation, but, aside from the im- 

 portant service it performs in holding together Ammophila or Populus 

 dunes until other vegetation can obtain a foothold, there is consider- 

 able evidence that on Presque Isle Andropogon may cause the forma- 

 tion of a dune independently of other dune-forming plants (see Plate 

 XXXVIII). 



Afidropogon furcatus is a bunch-grass growing in dense rounded 

 clumps, often two feet or more in diameter, and sending up flowering 

 stems to a height of two to three feet. Ordinarily the clumps on the 

 sand-plain are so far apart, that, although each individual clump forms 

 a miniature dune, there is no continuous accumulation of sand due to 

 the joint effect of several neighboring clumps. Occasionally, how- 

 ever, the clumps are so close together as to have such a joint effect and 

 a low dune is formed. 



The grass apparently grows more vigorously, if somewhat elevated 

 above the general surface of the sand-plain, and upon the new dune, 

 or upon an old Ammophila or Populus dune, the grass-clumps are 

 closer together, thus bringing about a greater ability on the part of 

 the grass as a dune-former. 



