438 Wisconsin Academy of Sciences, Arts, and Letters. 
question show as wide a distribution especially to the north as 
do the hog plants. 
The facts of distribution seem to indicate that the deciding 
factors in this case are chiefly edaphic rather than climatic and 
that the conclusions noted above as reached by Chamberlain and 
also by Whitson and Jones that the heath group is intimately 
connected with an merges into the forest, while the marsh type 
leads to the prairies is the more nearly correct. 
Horizontal Stratification 
The plants of the marsh show also a characteristic horizontal 
stratification that is generally considered as due to the light 
requirements of the different species. 1 
Recent investigations of Yapp (24) (1909) show that there 
are marked differences in the evaporation at the various levels 
and that this is an important factor in influencing the aerial 
structure of the various species. Close to the ground and shaded 
by the sedges and grasses there is a rather compact carpet like 
growth of moss covering most of the marsh. In the mixed 
associations low growing plants like Viola blanda and Parnas- 
sia caroliniana seem to also thrive in spite of considerable shad¬ 
ing by taller forms. 'Over much of the area Eleorharis palus- 
tris grows with slender weak culms seldom more than eight 
inches in height and which are abundantly scattered among the 
taller plants. This is true also of Car ex sterilis. 
There is further also what may he called a seasonable devel¬ 
opment which results in the successive ascendency of different 
species and a corresponding change in aspect of the whole flora. 
At several points in all the association where Car ex strict a and 
Calamagrostis canadensis were nearly evenly balanced in num¬ 
ber and frequence this was very clearly shown. In June and 
early July the Carices flower and reach their maximum de¬ 
velopment completely overtopping Calamagrostis, but in July 
and August the latter develops and forms a leafy stratum above 
the sedges and in some cases almost entirely masks the sedges 
below. The various Labiatae and Compositae also> develop 
late in summer or in the early autumn and by rather profuse 
