THE DUNES OF LAKE MICHIGAN 211 



in Holland, the absence of a well pronounced succession, such 

 as is found in the dunes of our country. 



In passing, a short remark may be made on some peculiar 

 representatives of the flora of Lake Bluff, Illinois. One of them 

 I have named already, Thuja occidentalis. We were told, that 

 this is a tree of relatively northern distribution, which on the 

 east side of Lake Michigan only occurs in the northernmost 

 parts. Yet it is included in the flora of Lake Bluff, which is 

 situated near the southwest corner of the Lake. This case be- 

 comes still more interesting, when we hear that it does not stand 

 alone and that the same holds true for several other species. 

 The second and third row of small dunes on the beach at Lake 

 Bluff were covered by Populus balsamifera, undoubtedly repre- 

 senting the cottonwood and conifer dunes of other places, ac- 

 tively moving dunes being absent here because of the feebleness 

 of the easterly winds, that determine this dune-area. This too 

 is a tree of relatively northern distribution, replacing at Lake 

 Bluff the cottonwood, Populus deltoides, which we might, for 

 instance, have expected from our studies of the dunes at Miller. 

 Another example is Juniperus Sabina procumbens, one of the 

 chief character-plants of the third row of the dune-area in ques- 

 tion. Finally we could mention Betula alba papyrifera, large 

 quantities of which grow on the forested cliffs near Lake Bluff. 

 It is certainly interesting to note that so many northern 

 species are found together here and it seems difficult to give an 

 explanation. 



Thus far we have mainly dealt with the influence of the fresh 

 water character of Lake Michigan on the adjacent territories. 

 The principal difference between the dunes in my country and 

 those of Lake Michigan is however caused by another factor. I 

 mean the value of the soil behind the dunes, which is much 

 higher in Holland than it is in the Chicago region. In conse- 

 quence thereof much more attention has been paid to our dunes 

 by man and great care has been taken to prevent them from 

 moving farther landward, As is generally known, this has been 

 attained by planting them with tufts of Ammophila arenaria, 



