tg11] BURNS—HURON RIVER VALLEY phe 
below the lowest level to which the water table gets in the driest 
times is red, while that above varies from red to brown and black. 
As has been pointed out, plants do not root in the red peat. 
Humidity 
Only a few readings were taken with some evaporimeters 
belonging to the Carnegie Institution and loaned by LivrncsTon. 
The total evaporation for seven weeks was as follows: under 
tamaracks in sphagnum, 275 cc.; on floating sedge, 321.7 cc.; 
in an adjacent oak-hickory grove, 860 cc.; in an open field border- 
ing the lake, 1056 cc. The last figure is short two days because 
the instrument was broken. These data, however, give conditions 
only near the surface, and are of value only in a study of germi- 
nation in the different zones. It has been pointed out recently 
(21) that great variations are found in short distances above the 
surface in the amount of water lost by evaporimeters. A lack of 
instruments made it impossible to study this phase of the subject. 
Light 
Light readings were made with the usual form of photometer. 
It was found that the light falling upon the tallest plants in all 
zones was approximately the same. Great differences were found 
between these values and those light values found at the surface 
in the different zones. With light value in the open as 1, the 
following values were found: under Chamaedaphne, 0.0026; 
under tamaracks, 0.033; under brambles found in a clearing 
society where maple and cherry seedlings were found in large 
numbers and some few individuals of each had reached a height 
equal to the brambles, the light was only 0.00022; among the 
leaves of the brambles it was 0.166. The value 0.033 seems to 
be the minimum light requirement for Chamaedaphne in the region 
about Ann Arbor. Fig. 8 shows dead Chamaedaphne at First 
Sister Lake where the light value was 0.033. 
The data recorded above show that the bogs of southern Michi- 
gan are for the most part not xerophytic habitats, but by far the 
largest areas are either hydrophytic or mesophytic. Only two or 
perhaps three of the zones can be considered as xerophytic habitats; 
