April, 1908.] The Vegetation of Cedar Point. 319 



During certain damp periods the agaric appears quite abun- 

 dantly and can quite appropriately be designated as a principal 

 species characterizing the Psilocyhe amniophila Society and deter- 

 mining a summer aspect of the formation. The secondary species 

 as may be noticed, are all invaders from the drift beach in front 

 or from the habitat behind the f ringing-dune. The secondary 

 species are never very abundant in the dune. 



The successor to the f ringing-dune is somewhat indefinite. 

 The Ammophila apparently dies out as soon as deprived of freshlv 

 drifting sand and, in case the beach grows outwards, the grass 

 dies out and the sand is blown away by the wind, or, in some cases 

 other dune plants may successfully invade the dune and hold the 

 sand in place. Among these latter may be mentioned Elymus 

 and Andropogon and, to some extent, Arctostaphylos. 



The Elymus Dune Formation. 



Facies: Flymus canadensis, 

 Elymus striatus. 



Secondary Species: 



Euphorbia polygonifolia, Artemisia caudata, 



Andropogon sco partus, Panicum virgatum, 



Tilia americana, Arctostaphylos uva-ursi. 



This formation is quite well represented along the Lake 

 shore to the south of the bathing pavilion of the pleasure resort 

 and it there apparently occupies an old Ammophila f ringing- 

 dune which has been left somewhat inland by the outward growth 

 of the land form at this place, so that the Ammophila has been 

 deprived of freshly drifting beach sand and has died out. 



The stage succeeding the Elymus Dune Formation is here a 

 mixed formation in which Tilia americana^^ and Juniperus 

 virginiana are prominent, this formation eventually giving way 

 to the Quercus velutina-imhricaria Forest Formation. 



The Andropogon Dune Formation. 



Facies: Andropogon scoparius, 



{Andropogon furcatus also to a limited extent.) 



Secondary Species: The secondary species are here about 

 the same as those in the Elymus Dune Formation and it is 

 not improbable that these two so-called formations may repre- 

 sent simply consocies of one and the same formation. Andro- 

 pogon scoparius, as is also the case with Panicum virgatum, 

 often forms about the separate clumps little dunes sometimes 

 reaching a height of a couple of feet, but these miniature dunes 

 disappear with the death of the grass and do not pass by succes- 

 sion into other vegetational structures. 



19. Cowles, H. C. 1. c. Bot. Gaz. 27 : 361-367. The Tilia dunes 

 are along parts of the Lake Michigan dune district an iinportant feature. 



