98 BOTANICAL GAZETTE [FEBRUARY 
Springs and spring brooks may be classed with ravine streams, 
but differ from them in the relative absence of erosion phenomena. 
This type of stream is uncommon in the Chicago area, though 
there are a few spring brooks near Chesterton. The water supply 
is much more constant than in ravine streams, and the shade of 
the ravines is often lacking. Besides the aquatics there may be 
mentioned a characteristic brookside flora, including such plants 
as Symplocarpus foetidus, Asclepias incarnata, Chelone glabra, Poly- 



Fic, 10.—Same island as shown in fg. 9, but seen from below, and showing the 
eee action of the river. Naked sand bar recently formed at the lower end of 
the island (left hand), Ambrosia farther Gite the right, willows on the older part of 
the island (extreme right). 
gonum sagittatum,and two or more species each of Eupatorium, 
Lobelia, Mentha, Lycopus, and Bidens. The most characteristic 
spring brook shrub is the alder (A/nus incana), though the exten- 
sive northern development of alder thickets has no parallel here. 
As the energy of the developing stream is checked, the con- 
ditions for plant life become more favorable. Inthe quiet pond- 
like waters of an older stream there may be found many of the 
aquatics that frequent the ponds and lakes. In fact the flora 
that is given later as characteristic of half-drained ponds and 
lakes (such as Calumet lake) may be transferred almost bodily 
to sluggish streams, such as the Calumet and Desplaines rivers. 
When streams are old enough and therefore slow enough to 
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