Jennings : A Botanical Survey of Presque Isle, 339 



such a drifting of the sand. A glance at the map of the peninsula 

 shows very plainly the preponderance of ponds and lagoons towards 

 the southeastern part of the peninsula. 



During the fruiting period of the cottonwood and of the sand-bar 

 willow, Sa/ix syrticola, the cottony disseminules of both of these 

 species are blown over the sand plain in great numbers by the westerly 

 winds, which prevail during fair weather, and the disseminules are thus 

 blown into the ponds and lagoons in such abundance as to collect 

 along the shores in little windrows. The right conditions for suc- 

 cessful ecesis, however, are to be found only in the young lagoons 

 near the lake-shore, where the shores of the lagoons are composed of 

 loose, rapidly accumulating sand, in which the seeds quickly become 

 buried and as quickly sprout. Along the shores of the older lagoons 

 the disseminules collect as abundantly, but the shores being composed 

 of more firmly packed sand, the seeds do not become buried and so 

 cannot accomplish ecesis. Along the Iake-bea(ph ecesis is effectually 

 prevented by the mechanical violence of the waves. 



At Presque Isle it was found that the cottonwoods always sprouted 

 in the loose sandy shore of lagoons not more than three or possibly 

 four years after the separation of the lagoon from the lake. It is in- 

 teresting to note that Whitford found in the Philippine Islands the 

 "mangrove a.v\d Nipa-Acaiitkiis formations behind sandy beaches" 

 having methods of dissemination and ecesis very similar to those just 

 described for the Populus-Salix formation at Presque Isle. In both 

 instances the disseminules first float upon areas of quiet water protected 

 by bars or beaches and both find the dynamic conditions of the strand 

 too strenuous to admit of their obtaining a foothold.'" 



Wherever, as towards the southeastern part of the peninsula, the 

 lagoons are less exposed to drifting sand, the vegetation generally 

 passes through a marsh-succession and no dunes or ridges are formed. 

 Where the sand is drifted in more abundantly, however, it tends to 

 accumulate in the line oi Populiis and Salix surrounding the lagoon, 

 thus beginning the formation of the dune. Most of the lagoons being 

 long narrow ponds parallel to the lake-shore, the dunes formed along 

 the line of trees arising on the banks of the lagoon also have a direc- 

 tion parallel to that of the lake-shore. 



'"Whitford, H. N. "The Vegetation of the Laraao Forest Reserve." Philip. 

 Journ. Science, I : 673-674, 1906. 



