112 BOTANICAL GAZETTE | FEBRUARY 
where, upon the content and values of the terms employed; 
this disagreement is but an expression of the fact that there are 
few if any sharp lines in nature. The above, or any other ter- 
minology, is largely arbitrary and adopted only as a matter of 
convenience. J 
In the following pages an attempt is made to arrange th 
plant societies in the order of development, the author's belief | 
being that this order more faithfully expresses genetic relation 
ships than any other. In the historical development of a region : 
the primitive plant societies pass rapidly or slowly into others; | 
at first the changes are likely to be rapid, but as the plant 
assemblage more and more approaches the climax type of the 
region, the changes become more slow. In the dune region of ‘ 
Lake Michigan the normal primitive formation is the beach; 
then, in order, the stationary beach dunes, the active or wa \der- 
ing dunes, the arrested or transitional dunes, and the passiv 
established dunes. The established dunes pass through sel 
stages, finally culminating in a deciduous mesophytic forest, Ut) 
normal climax type in the lake region. Speaking broadly, & 
conditions for plant life become less and less severe through # i 
these stages, until there is reached the most genial of all « 
ditions in our climate, that which results in the production of & 
diversified deciduous forest. On the beach there are ne 
the order of genetic succession, these xerophytic StU 
become less and less pronounced, finally culminating ! 
typical mesophytic structures of a deciduous forest. 
A. THE BEACH. 
As the author hopes to show in a subsequent pape 
beach formations of Lake Michigan are of two distinct | 
One may be called the xerophytic beach, the other the , 
phytic beach. The conditions that determine these two 
are not altogether clear, though their distribution g. 
some factors which will contribute to the solution of the 
lem. Dunes are invariably absent from an area occup!* 
