THE ECOLOGICAL RELATIONS OF THE VEGETATION 
ON THE SAND DUNES OF LAKE MICHIGAN. 
PART I.—GEOGRAPHICAL RELATIONS OF THE DUNE 
FLORAS. 
CONTRIBUTIONS FROM THE HULL BOTANICAL 
LABORATORY. XIII. 
HENRY CHANDLER COWLES. 
(WITH FIGURES I-26) 
I. Introduction. 
THE province of ecology is to consider the mutual relations: 
between plants and their environment. Such a study is to 
structural botany what dynamical geology is to structural geol- 
ogy. Just as modern geologists interpret the structure of the 
rocks by seeking to find how and under what conditions similar 
rocks are formed today, so ecologists seek to study those plant 
structures which are changing at the present time, and thus to 
throw light on the origin of plant structures themselves. 
Again, ecology is comparable to physiography. The surface 
of the earth is composed of a myriad of topographic forms, not. 
at all distinct, but passing into one another by a series of almost 
perfect gradations; the physiographer studies landscapes in 
their making, and writes on the origin and relationships of topo- 
graphic forms. The ecologist employs the methods of physiog- 
raphy, regarding the flora of a pond or swamp or hillside not 
as a changeless landscape feature, but rather as a panorama, 
never twice alike. The ecologist, then, must study the order of 
*uccession of the plant societies in the development of a region, 
and he must endeavor to discover the laws which govern the 
ee changes. Ecology, therefore, is a study in dynamics. 
its most ready application, plants should be found whose 
tissues and o 
| i in 
1899) "Bans are actually pee at the present time 
