48 MISSOURI BOTANICAL GARDEN. 
marshy with the exception of the northeastern end, where 
the lower level of the ground has permitted an outlet into 
Lake Michigan. (Plate 7.) As no large volume of water 
overflows, it has not succeeded in cutting out a well-defined 
channel. The rapidly growing vegetation has assisted in 
the partial damming of this small stream, so that it has 
gradually spread out until quite a large area is now occupied 
by its meanderings. The current, although exceedingly 
sluggish, has a general onward movement, slowly changing 
the water about the roots of the vegetation. Probably 
from this cause or one related to it, the vegetation is strik- 
ingly different from that in the last described area. The 
largest tree in this swamp is the white pine (Pinus Strobus), 
but the dominant one is the arbor-vitae (Thuya occiden- 
talis), here growing to great size, fifty feet in height and 
twenty inches in diameter. A great many dead and dying 
trees are found, but whether they have lived out their nat- 
ural existence or died from lack of sufficient nourishment, 
it is impossible to say. The fall of these dead trees has 
been attended by the uplifting of great masses of earth and 
organic debris which have united to form large hummocks 
throughout the swamp and the existence of these hummocks 
has determined the vegetation to a great degree. This great 
tract of trees and undergrowth amid a mass of fallen logs 
and brush forms a dense jungle of vegetation which is 
almost impenetrable. 
Next in importance to the arbor-vitae comes the white 
ash (Fraxinus Americana), the only deciduous tree ob- 
served except an occasional yellow birch (Betula lutea) 
encroaching from the marginal forests. Abies balsamea 
is frequently found here. In a rather similar area studied 
on Beaver Island, Mich., the tamarack is quite abundant 
as is also the paper birch (Betula papyrifera). The prin- 
cipal shrubs occurring near the margin or upon the hum- 
mocks are second growth arbor-vitae, Acer Pennsylvanicum 
and A. spicatum. The yew (Taxus Canadensis), which 
