Jennings : A Botanical Survey of Presque Isle. 



309 



different structures, or different names for the same structures. As to 

 synonymous terms, in recent ecological literature, series has often 

 been used for succession, as herein defined, society for formation, and 

 association for consocies. 



Some ecologists will, perhaps, take exception to the rank of forma- 

 tion which has been herein accorded certain vegetational structures, 

 especially in the Lagoon Succession, but the corresponding habitats 

 appear, even without instrumental determination, to be so clearly dis- 

 tinct and their plant-life so plainly a definite and correlated structure 

 as to merit the rank of formation. 



The Beach-Sand Plain-Heath-Forest Succession. 



A comparatively large part of the land area of Presque Isle is to be 

 referred to this succession. It includes all of the more northern and 

 lakeward portion of the peninsula, commencing a short distance north- 

 west of the Key Post (see map) and extending west and southwest. This 

 succession resembles very closely in many respects the Beach-sand Plain- 

 Thicket-Forest Succession adjoining it immediately on the south and 

 southeast, and probably should be regarded as a part of the same 

 succession, which has a more xerophytic habitat, being exposed to the 

 full force of the more violent and colder prevailing winds from the 

 west and northwest, and on this account is invaded by certain for- 

 mations from the Northern Coniferous Forest Center, of which more 

 will be said later. 



The Beach. 



As stated in the discussion of the physiographic origin and develop- 

 ment of the peninsula, the shore-line at the eastern end of the peninsula, 

 within the area embraced in the succession under consideration, grows 

 outward either by the direct accumulation of detritus upon the beach 

 or by the formation of sandbars, behind which the shallow lagoons 

 are often quickly filled with wind-driven sand. In either case the 

 result is a wide stretch of beach, the sand of which when dry is 

 readily blown about by the wind. This beach constitutes the same 

 xerophytic structure so common along the shores of all the Great 

 Lakes. The beach along the shores of Lake Michigan, so thoroughly 

 studied by Cowles,^" is practically duplicated here on Presque Isle, 

 and, following Cowles' classification, there may be distinguished 

 two habitats in the beach proper : the Lower Beach and the Drift- 

 Beach. 



""Cowles, H. C. /. c. Bot. Gaz., 27 : 114-II7, February, 1899. 



