32 I^uLLETiN Wisconsin Natural History Society [Vol. 12, Nos. 1 & 2 
taiiical viewpoint to prove that such processes operate. Fortu- 
nately, in the case of l)og vegetation we have the added geological 
evidence furnished by vertical sections through bog substrata in 
ditches and in drillings for peat. A photograph of a section of a 
ditch near Vestaburg, Michigan, which has been published by 
Davis (1907, plate 13) shows the layers of vegetation deposited 
in the bog through which the ditch passes; from the surface of the 
bog downwards these various layers are, successively, (a) living 
sphagnum, (b) sphagnum peat, (c) shrub remains, (d) sedge root- 
stocks, (e) pond lily rootstocks, and (f) laminated peat. We find 
today in Ridgeway Bog, and elsewhere in the region, certain char- 
acteristic animals associated with these various bog plant asso- 
ciations; we do not know whether plants per se are responsible 
for this hal)itat preference on the part of the animals, or whether 
physical and physiographical factors, through which the differ- 
ent plant associations are the outcome, are directly responsible; 
perhaps in some cases one is the cause of habitat preference, in 
others the other, and in still others a combination of the two may 
determine the preference; animal associates, it seems, must also 
play a large part in habitat preference. However that may be, 
accompanying the zonation of plants in Ridgeway Bog there is a 
definite zonation of animals, and accompanying plant succession 
in Ridgeway Bog there is an associated animal succession. 
The Cedar-Balsam-Hemlock Association might not be the cli- 
max association for it prol)ably would be succeeded by a coniferous 
forest of a different character, or more probably, as there is some 
evidence to believe, ultimately by a deciduous forest association, 
‘dtrganisms which remain in one place do nothing which tends to 
remove the results of their own existence, and frequently modify 
their environments in manners detrimental to themselves. On the 
land, plants are the dominant sessile forms, and often profoundly 
modify the conditions in which they live, so that they cannot 
succeed themselves. When will the process of succession stop? 
Obviously, it must cease when there are no available species to 
take the place of those which have destroyed their own habitat. 
There are species which are immune to their own products and the 
l^roducts of the species which are associated with them. Ob- 
viously, when a condition in which these species can live is 
reached, and they come to occupy the place which is thus made 
ready for them, the formation which they constitute can, so far 
