220 MICHIGAN SURVEY, 1908. 



except an area of open water about 60 feet long and half as wide 

 surrounded by an exceedingly wet, unstable margin. 



A few years hence and even this will be covered. The main part of 

 the bog was covered with sphagnum hummocks, upon which were grow- 

 ing Ledum groenlandicum, Chamaedaphne calyculata and Andromeda 

 polifolia in dense patches. Young Tamaracks and Black Spruces were 

 pushing out from the older parts of the margin, with Balsam Firs close ' 

 behind. 



Along the south margin of this bog, in the tension zone between the 

 bog and the adjacent forest, there was being waged one of the most 

 intense and most interesting struggles for plant supremacy that we 

 have ever seen. Working up the gentle slope from the bog margin the 

 sphagnum invasion (after the manner of a large snowdrift) was push- 

 ing out its lobate fingers, over the forest carpet of leaves; and during 

 a single season by its rapid growth had surrounded such plants of 

 the forest as Aralia nudicaulis, Trientalis americana, Clintonia horealis, 

 Lycopodium lucidulum, all of which were completely helpless in the 

 path of the sphagnum invasion. Even large, fallen trees were able 

 to check its advance only temporarily, for instances were noted where 

 entire fallen trunks were covered, only the upward projecting branches 

 being out of reach of the Sphagnum. In a dry carpet of forest leaves 

 the clean-cut forward margin of the sphagnum was so wet that water 

 could be wrung from it at a distance of 1.5-20 feet from the original 

 bog margin, thus showing how readily water is transferred through the 

 sphagnum patches, even up a slope. 



While the sphagnum invasion was eminently successful against all 

 the scattered plants of the woods there was at least one species of 

 moss (Polytrichum commune) growing in dense formations which was 

 successful in holding the sphagnum in check. The moss colonies were 

 so dense that the sphagnum could not penetrate them; on the other 

 hand the moss was actually invading the moist sphagnum and growing 

 over it. ' 



Before leaving the semi-enclosed lake bogs a few questions suggest 

 themselves regarding tJie trembling bog carpet adjacent to the water's 

 edge. What is the thickness of this elastic, quaking water cover which 

 is, at the same time, strong enough to enable one to walk out to with- 

 in a single step (in some cases) of the water's edge? Also of what is 

 it composed? In all the measurements taken it was found that this 

 vegetative cover, within two to three feet of the water's edge, had a 

 thickness varying from 22-24 inches. Back from this younger and more 

 unstable margin the bog cover becomes thicker and firmer. In one bog, 

 back about 100 yards from the water's edge, where the surface was 

 firm and unyielding, the boring pole broke through into open water at 

 a depth of 5 feet 6 inches. In another instance, at the west end of 

 Sumner Lake, at a distance of over 100 yards back from the water's 

 edge, I found the bog cover still so thin and trembling that I broke 

 through in one place in attempting to walk across it, and anticipated 

 that the same might happen in several other places. These and other 

 instances all go to show that no definite statement can be made as to 

 the exact distance from the water's edge at which the bog cover be- 

 comes thick enough to support one. This may vary with the depth 

 of water underneath, as well as the distance from the original shore 



