118 BOTANICAL GAZETTE . [FEBRUARY 
of the island, has been the occupation by vegetation of new areas 
left exposed by the retreating waters. Recession has now ceased, 
temporarily at least, and no fresh surfaces have been presented for 
a long period of time. The forest in its advance has for this reason 
in some places practically reached the limit of possible growth, 
being prevented from further extension by wave and ice action. 
In these places the forest is seen extending in its full development 
to a line where it ends abruptly, being separated from the water 
by a strip of nearly bare rock shore. At other points invasion is 
still actively in progress, and the transition from bare shore to 
mature forest is a gradual one. It is in such situations as these 
that the various stages in the succession are seen in their best 
development. 
On all the types of rock shore, cliff and sloping, protected and 
exposed, of all kinds of rock, the successional stages and processes 
are in general essentially the same. There are, however, important 
modifications due to the differences in habitat just mentioned. 
ong them are telescoping, suppression, or elimination of certain 
stages, and variations in rapidity of invasion. In the following 
paragraphs the complete series of stages which constitute the rock 
shore succession will be first described, with the understanding 
that rarely will this series be found in absolute entirety. After- 
ward the modifications of the series associated with the different 
types of rock shores will be discussed. 
a) The complete series 
In tracing the early stages of the rock shore succession we find 
three separate lines of advance, which may conveniently be termed 
subsuccessions. They are the rock surface subsuccession, the crevice 
subsuccession, and the rock pool subsuccession. Later these unite, 
and the development proceeds thenceforth along a single line. 
1. The rock surface subsuccession——We have here mainly a 
study in the ecology of lichens, to which adequate treatment can 
be given only by a specialist in that group. The general sequence 
of stages has been frequently described in ecological papers, as by 
WauitForp (59) for the southern shore of Lake Superior. Crustose 
lichens are the first plants to appear, and are accompanied by xero- 
