269 



the Potcntilla, the composite, the Bqnisctum, and the convolvulaceous 

 plant, for they were growing in the bottom of it. The nearest source 

 for the Jiiniperus was about a hundred meters away, from which the 

 seed may have been carried by the gulls which are abundant on the 

 beach and occasionally are seen in the heath. Close to the lee (south- 

 west) side of another piece of embedded wreckage in this same vicin- 

 ity was a straggling plant of Xanthiuin commune (cocklebur). 



Taking all these facts into consideration, it seems evident that a 

 new ridge is being thrown up. The pieces of wreckage were prob- 

 ably lodged there during the violent storm and tidal wave of May 12, 

 1905. The juniper came in in the backwash of that storm or by some 

 other agency, as suggested above, in 1906, as it appeared to be three 

 or four years of age (1909). The storm and tidal wave of April 29, 

 1909, did not dislodge the wreckage nor the juniper. It added ma- 

 terial that can assist in the formation of a ridge. Progress towards 

 that end, however, is very slow. 



The Chlamydomonas association is entirely identical with the 

 CJilamydomoiias formation of Jennings at Cedar Point (1908:313) 

 and at Presque Isle (1909:310). Occasional presence of the alga 

 was reported by Cowles near Porter, Indiana, (1899:114). This 

 association, together with the plantless area, composes what MacMil- 

 lan termed the "front strand." 



The Cakilk-Xanthium Association 



From the upper limits of the open sand of the middle beach, and 

 therefore out of reach of the ordinary storm-waves, an area of 

 sparsely vegetated sand stretches inland. This is the location of the 

 Cakilc-Xantliium association. The landward boundary of this area 

 is usually the fringing dune. 



Physical Environment. — The physiographic characteristics of this 

 association are fully discussed by Cowles (1899:115-117) and by Jen- 

 nings (1909:311). The middle beach, as Cowles designated it, lies 

 "between the upper limits of the summer and winter waves." It is 

 dry in summer, and differs from the lower beach only in that it is not 

 subject to the mechanical violence of the waves during the growing- 

 season. The soil is, for the most part, sand whose grains vary be- 

 tween 0.2 and i.o mm. in diameter. It is exposed to the full force 

 of wind and sun, and conse(|uently it is very dry nearly all of the 

 time. During the daytime the sand may become very hot (60° C), 

 but it cools off rapidly during the evening. Although the upper few 

 centimeters are so very dry, the sand beneath is always moist and 

 may even be wet. 



