310 Annals of the Carnegie Museum. 



The Lower Beach. — The Chla?nydomonas Formation. 



The lower beach extends from the ordinary shore-line back to the 

 average highest point reached by the waves of the ordinary summer 

 storms. At Presque Isle it occurs quite uniformly around the entire 

 lake shore and much of the bay-shore. Essentially equivalent to 

 this lower beach is MacMillan's " front strand, "^^ Schimper's " fore- 

 shore " ^^ and Cowles's " lower beach." ^" 



At Presque Isle the lower beach is practically devoid of all plant- 

 life of a permanent nature. Living fragments of Vallisneria and 

 Potamogeton were often found half buried in the sand, and on one 

 occasion, a rhizome of Castalia with living shoots, but none of these 

 plants ever become established. During continued damp weather 

 without high waves a motile single-celled alga, ChIamydomo7ias s^., 

 occasionally appeared in the damp sand, causing a distinct green col- 

 oration. The same thing was observed by the writer in 1905 on the 

 lower beach of Cedar Point, Ohio," and was found also by Cowles^' 

 on the lower beach of Lake Michigan. As Cowles points out, the 

 alg^ being motile, can move about freely in the capillary water of the 

 wet sand and it appears that they are really to be considered as 

 migrants from the waters of the lake rather than as inhabitants of the 

 beach. 



The lower beach, as a habitat, offers very severe conditions for 

 plant-life. When washed by the waves the habitat is, of course, 

 truly hydrophytic, but when lying exposed to the sun in clear quiet 

 weather, the sand, at least on the surface, becomes very dry and hot, 

 extremely xerophytic, and these extreme conditions, taken together 

 with the mechanical violence of the waves and the very unstable 

 character of the soil, washed about by the waves when inundated, or 

 in quiet weather becoming dry and being blown about by the wind, 

 make establishment impossible for any of the plants of the region, 

 aside from the alga mentioned. 



3' MacMillan, Conway. " Minnesota Botanical Studies — Observations on the 

 Distribution of Plants along Shore of I-ake of the Woods." Geol. & Nat. Hist, 

 Survey Minn., Bull. 9: 969. 1897. 



32 Schimper, A. F. W. /. c, p. 180, 



3* Cowles, H. C. /. c. Bot. Gaz., 27 : I13-I15, February, 1899. 



3^ Jennings, O. E. "An Ecological Classification of the Vegetation of Cedar 

 Point." Ohio Naturalist, 8: 291-340, April, 1908. 



