April, 1908.] The Vegetation of Cedar Point. 313 



The Lower Beach — The Chlamydomonas Formation. 



Following in part Cowles' classification^^ of the beach habitats, 

 there ma\' be distinguished, first, the Lower Beach, ^■'^ comprising 

 that part of the beach washed by the waves of ordinary summer 

 storms and thus, chiefly by reason of the mechanical violence of 

 the waves and the instability of the sub-stratum, practically 

 devoid of plant life. However, as Cowles noted along the lower 

 beach of Lake Michigan and as the writer found also on the 

 Lower Beach of Presque Isle, a species of Chlamydomonas , a one- 

 celled motile alga, occasionally occurs so abundantly in the sand 

 as to cause a distinctly green coloration These plants are per- 

 haps more correctly to be regarded as migrants from the waters 

 of the Lake, but, being so abundant in certain wet periods and 

 being also the only plant found commonly in the habitat, we 

 have termed the formation the Chlamydomonas Formation. 



The Drift Beach — The Cakile-Xanthium Formation. 



Extending from the upper limit of the waves of ordinary 

 summer storms, i. e., the upper edge of the Lower Beach, up to 

 the upper limit of the waves of severe winter storms, there is a 

 zone which may be termed the Drijt Beach, ^* which is character- 

 ized ordinarily by freedom from the violence of the waves of 

 summer storms but is subjected to severe mechanical action of 

 the waves of winter storms, at which time there is usually left a 

 line of driftwood which marks, through the following season, 

 the upper extent of the wave action. 



The habitat as thus characterized is inhabited by a vegetation 

 composed of such annuals as can endure the summer environ- 

 ment, the seeds having been left in their present position by 

 wave action. Perennials and biennials are, of course, barred 

 from this habitat by the destructive eflects of wave action during 

 the winter. The habitat presents above the surface of the 

 sand conditions of excessive insolation, great and often very 

 sudden extremes of temperature, great fluctuation in the water 

 content of the air, and, also, high winds, and is thus distinctly 

 xerophytic. The edaphic conditions are, however, distinctly 

 hydrophytic below the surface layer of sand so that the habitat 

 may, as a whole, be designated as dissophytic.^'^ The vegetation 



12. Cowles, H. C. The Ecological Relations of the Vegetation of the 

 Sand Dunes of Lake Michigan. Bot. Gaz. 27 : 95-117, 167-202, 281-303, 

 and 361-391. Feb., Mar., Apr., and Alav, 1899. 



13. Cowles, H. C. I.e. Bot. Gaz. 27 : 114-117. 



14. MacMillan's "Mid-strand" (Lake of the Woods); Schimper's 

 "Mid-shore"; Cowles' "Middle Beach" (Lake Michigan); Ganong's 

 "New Beach" (Miscou Island); are all synonyms for the habitat here 

 designated as the Drift Beach. 



15. See Clements — Research Methods in Ecology. 



