224 ILLINOIS STATE ACADEMY OF SCIENCE 



Complete lists of the species found in the different bogs 

 have not as yet been completed, but an examination of the 

 lists of the dominant species (Fig. 8) shows interesting 

 anomalies. Apart from the absence of the usual bog 

 plants in 7 and 8, the dominance of chamaedaphne in 5 

 and of andromeda in 2 is the most striking. These two 

 bogs are very similar in all other respects and there is no 

 obvious explanation of this marked difference in the pres- 

 ence of two species so closely related both taxonomically 

 and ecologically. 



Another point of great interest is the maturity and the 

 rate of development of the bog mat in the different de- 

 pressions. Bogs 1, 4, 7, 8, and 9 (Fig. 8) show by the 

 condition of the substratum and the presence of members 

 of the upland forest that they have reached a condition 

 of considerable maturity, while 6 is intermediate and 3 is 

 very young. Furthermore, the evidence, both from the 

 formations themselves and from human testimony, shows 

 that there has been a very rapid increase of bog mat 

 formation within the memory of man. If these bogs have 

 been in existence since the glacial period, as has been the 

 generally accepted view, it is necessary to account for the 

 sudden speeding up of their development in recent years. 

 If, on the other hand, No. 3 is of recent origin, it is 

 equally difficult to explain how the conditions which pre- 

 vented its origin for a very long period became changed 

 so as to permit its start in recent years. From observa- 

 tions of these bogs and also of similar formations in Ben- 

 zie County, Michigan, (5, p. 27) it is the opinion of the 

 writer that a recent lowering of the water levels in all 

 of these depressions may have caused the change in con- 

 ditions which made possible a recent increase in bog mat 

 formation. Further study will be necessary before any 

 final decision can be reached on this question. 



LITERATURE CITED. 



1. Burns, G. B., A botanical survey of the Huron River valley. VII. 



Bot. Gaz. 47:445-453. 1909. 



2. Rigg, Geo. B., A summary of bog theories. Plant World. 19:310-325. 



3. Transeau, E. N., Bogs of the Huron River Valley. IV. Bot. Gaz. 



41:1-42. 1906. 



4. Waterman, W. G., Preliminary report on the bogs of northern Illi- 



nois. Trans. 111. State Acad. Sci. 14:79-84. 1921. 



5. Development of plant communities of a sand ridge 



region in Michigan. Bot. Gaz. 74:1-31. 1922. 



