1899] DUNE FLORAS OF LAKE MICHIGAN 169 
upper beach. A species scarcely less important in this connec- 
tion is the beach pea, Lathyrus maritimus, another marine plant; 
locally the beach pea is often the dominant character plant, 
especially northward. Three other species are character plants 
over wide areas, as the above three are throughout. Euphorbia 
polygonifolia is a character plant at many stations between Chi- 
cago and Glen Haven; its absolute abundance is often as 
marked on the upper as on the middle beach, though its relative 
importance is much greater on the latter. Agvropyrum dasysta- 
chyum and Gfnothera biennis are as characteristic of upper beaches 
northward as Euphorbia is southward; Agropyrum especially is 
usually a dominant character plant north of Glen Haven. 
None of the above six species are confined to the upper 
beach. Artemisia is found in most dune societies inland, espe- 
cually. in comparatively naked places. Cnicus is frequent on the 
dune complex, though less abundant than on the beach, as is 
also true of Artemisia. Lathyrus appears to be more restricted 
mn its habitat, and in that sense is more typical of the upper 
beach, though it sometimes occurs on clay bluffs. Euphorbia 
ne i middle beach and also on naked dunes, though 
upper ae 2: Agropyrum, though characterishe of northern 
dunes. CE €s, is still more characteristic of the embryonic 
* ““nothera occurs on oak dunes and commonly also as a 
mesophyte, 
CAS it will be well to emphasize one of the funda- 
tively ee aa ecological plant groupings. It is compara- 
Perfectly Deak a ied single Species can be regarded as 
ten species Se of a formation, while a group of five or 
formation almost os Selected as to enable one to detect that 
Ye Six specie anywhere within a large area. No one of the 
“per beach oe can be regarded as perfectly typical of the 
together they for ough Lathyrus approaches such a type, but 
other formation mM an assemblage that cannot be found in any 
€N dunes. ae perhaps locally on the closely related 
Upper beach oo. oa these beach dunes, which grade into the 
; relative proportions existing between the above 
