International Excursion in America. 
325 
proportion of the week spent at Chicago was devoted to the 
vegetation of these dunes, already well-known to students of 
ecology from Professor Cowles’ paper in the Botanical Gazette for 
1899. An exceedingly useful pamphlet on “The Vegetation of 
the Chicago Region ” was distributed to the members of the party, 
including a summary of the plant-associations with lists of species. 
Chicago Sand Dunes. 
The succession of plant-associations on the sand-dunes of the 
southern shore is very complete, well-marked and constant, leading 
from a beach association—very poor floristically like the maritime 
sandy beach associations of temperate regions in general, and 
including Cakile and such forms as Corispermum hyssopifoliuvi , 
Euphorbia polygonifolia, Cirsium Pitcheri —through a fore-dune 
association characterized by sand grasses such as Awmophila and 
Calamovilfa , and by willows and sand-cherry, to a cottonwood 
association characterized by Populus deltoides, and occupying many 
of the large mobile dunes. From this point onwards the succession 
changes its character, owing to the protection from wind afforded 
on the landward side of the high mobile dunes ; and the vege¬ 
tation undergoes rapid stabilization and a subsequent succession. 
According to one American member of the party a sand prairie 
grass association in which the bunch grass ( Andropogon scoparius) 
figures, can often be distinguished as the initial phase of 
this succession: the prairie grasses are quickly succeeded by 
pines ( Pinus strobus —largely cut out on account of the value of 
its timber—and Pinus Banksiana, the dominant species), with 
which jfuniperus virginiana and Thuja occidentalis are mingled. 
This pine-association has a very characteristic undergrowth of 
jfuniperus communis , Arctostaphylos Uva-ursi, Pyrola spp., etc. 
Under the shade of this vegetation humus begins to develop in 
quantity for the first time. The pine-association soon begins to be 
invaded by the black oak (Quercus velutina), and a crowd of the 
less sciaphilous woodland shrubs and herbs. The pines are rapidly 
suppressed, and the typical black oakwood, often open, but in many 
places with a closed canopy, is established. This association 
forms a zone at least two or three miles wide in some places. 
• • • • 1 
Here and there in the hollows are small lakes and marshes 
representing detached portions of “Lake Chicago ” which have not 
been overwhelmed by the dunes, and showing all stages of succession 
from open water, through reed swamp, to an association of 
willows, etc., with other swamp-loving trees. Whether these areas 
