Jennings : A Botanical Survey of Presque Isle. 323 



tends out to the open slope leading directly down to the waters of the 

 lake, and which marks the extent to which the lake had worn away 

 the land prior to the erection of the jetties by the government. At 

 the summit of this slope there are, in a few places, small patches of 

 Arctostaphylos, and some Jiinipenis, representing remnants of the 

 heath, but the invasion by the Finns Strobus formation usually begins 

 quite early in the life of the heath and, as a result, the pine forest 

 presents along this part of the shore an almost unbioken front. 



In the most northwesterly and xerophytic portion of the pine forest 

 there is practically no outer shrub zone, other than the heath, but 

 farther inland to the east, where the exposure to the lake winds is not 

 so great, the conditions are more mesophytic and there is a gradual 

 transition into what maybe called a mixed formation in which species 

 oi P rutins, Acer, etc., are prominent. A discussion of this formation 

 will be taken up later. 



In the Finus Strobus forest formation there is comparatively very 

 little of the layering which is so characteristic of most hardwood 

 forests. There are in places a very few trees of the wild black cherry, 

 Friinus serotina, also P. petmsylvanica, which are generally of about 

 the same height as the pines and are being gradually killed out by 

 their dense shade. Jutnperus virginiana occurs occasionally as a relict 

 from the heath, but it apparently does not accomplish ecesis in the 

 white pine forest. 



There are but few seedlings of white pine in the typical part of the 

 formation. It appears that at Presque Isle, as has been found else- 

 where,'^* the seedlings of the white pine cannot endure the dense shade 

 of the mature white pine forest. If other trees are available which 

 can endure this shade during the seedling stages the white pine will 

 finally be replaced by a forest of other species. At Presque Isle the 

 black oak, Quercus velutina, is present very sparingly as a seedling in 

 the heath, but it becomes more and more abundant in all sizes as the 

 mature pine forest is approached and, upon the death of the white 

 pine, its place is occupied by black oak. Black oak appears to be 

 capable of accomplishing ecesis without difficulty, both in the heath 

 and in the dense pine forest ; its appearance in the latter in greater 

 numbers being due to circumstances of dissemination rather than to 

 its particular adaptability to the habitat. Some acorns may reach the 

 sand-plain also, but as Britten found on the North Haven Sand- 



^ Spring, S. N. /. c, p. 20. 



