164 BOTANICAL GAZETTE [MARCH 
B. The coastal group. 
I, THE LAKE BLUFF SERIES. 
The plant societies that have been discussed hitherto may be 
found in many if not‘in most inland districts. The societies that 
follow, on the other hand, are best worked out only in connec- 
tion with the coasts of oceans or great lakes. Theoretically a 
bluff may be composed of any kind of rock or soil, but those of 
our area are composed of morainic clays, and the life histories 
that follow will not hold good in other conditions. It may be 
noted here that there is a short stretch of rocky shore with litho- 
phytic algae at Cheltenham, but there is nothing that in any way 
approaches a rock cliff. 
Wherever a sea or lake erodes rather than deposits, there is 
commonly developed a sea cliff of greater or less dimensions. 
The material which is thus gathered may be deposited elsewhere 
in the form of beaches and later the wind may take up the sands 
from the beach and form dunes. The Chicago area gives splen- 
did examples of these two types of sea activity; to the north of 
the city is an eroding coast line with its bluffs, and to the south 
and southeast is a depositing coast with extensive areas of beach 
and dune. 
The lake bluffs at Glencoe give an excellent opportunity for 
the study of the life history of a sea-cliff vegetation. There 
can be almost no other ‘habitat in our climate which imposes 
such severe conditions upon vegetation as an eroding clay bluff. 
The only possible rival in this regard is a shifting dune, and even 
here the dune possesses some points of advantage so far as the 
establishment of vegetation is concerned. In the first place, the 
conditions as to exposure are almost identical with those of a 
dune: the heat of midday and of summer and the cold of night 
and winter are extremely pronounced; the intensity of the light 
and the exposure to wind make the conditions still more severe: 
In other words the only plants that can grow on these lake bluffs, 
at least in the earlier stages, are pronounced xerophytes. Again 
the character of the soil is unfavorable, for while the clay is wet 
in the autumn, winter, and spring, it dries out in the summer and 

