Jennings : A Botanical Survey of Presque Isle. 305 



still broke over into the bay. During a gale in 1874 a breach occurred, 

 but this was promptly closed and bulk-head protections built. 



During the winter of 1881-1882, in 1892-1893, and again in 1905- 

 1906, the waves have washed over the the neck but no real breach has 

 occurred. During 1 905-1 906, however, there was considerable ero- 

 sion of the neck, especially behind the old pile-protection (see Map, 

 Plate XXII). In places the beach receded at least thirty feet. 



The shoaling of the bay inside the neck is progressing quite rapidly 

 and, although the outer shore may wash away, it is probable that the 

 neck of the peninsula will be simply shifted to the east instead of 

 being entirely swept away. It has been stated that this section of 

 the peninsula is increasing in mass below the water's edge, although 

 the part above the water remains about the same, the distance between 

 the twelve and fifteen feet depth contours, outside and inside being, 

 in 1878, about double what it was in 1839."' 



From the above considerations it is to be seen that the main portion 

 of the neck of the peninsula is of approximately the same age as is 

 much of the sand-plain to the northeast of the Long Ridge and, as 

 will be shown later, its vegetation for this reason is also very similar 

 to that of the sand-plain. 



The Ecological Structure and Development of the Vegeta- 

 tion OF Presque Isle. 



General Considerations . 



All plants are intimately related to more or less definite conditions 

 of environment. These conditions are not always plainly evident, 

 but each species exists-within an environment characterized by definite 

 biological and physical features. 



In nature any given area always presents more or less constant and 

 definite conditions of environment. Such local conditions will neces- 

 sarily correspond more nearly to the environment required by some 

 species than by others, and thus there will arise in the vegetation as a 

 whole a grouping and localization of certain species. 



The unit of vegetation is the formation. Plants are everywhere 

 found associated ; their association being the joint result of repro- 

 duction and the conditions of environment. To quote Clem- 

 ents : '- "Association in its largest expression, vegetation, is essentially 



-'Nelson, S. B. /. c, p. 417. 



22 Clements, F. E. " Research Methods in Ecology," p. 202, 1905. 



