IIT] BURNS—HURON RIVER VALLEY SIO 
land, he dug a ditch from the margin to the open water during 
the dry season of 1903. As soon as his ditch was opened, the 
water flowed from the open lake to the margin and he lost the use 
of the land entirely. 
These examples show that there is very little movement of 
water in peat. The water may be several feet higher in one zone 
than in an adjacent one; the difference in height depends upon the 
nature of the peat. This fact is well known to persons traveling 
on northern bog areas. 
The variations here shown to occur in the position of the water 
table in different zones during the summer and in the same zone 
during the season, bring very strong additional proof to the state- 
ments of Davis regarding the xerophytic structures of bog plants, 
which were quoted above in the discussion of bogs during a dry 
period of years. During the season the plants growing in these 
bogs are subjected to high water level in the spring, when the 
water table in all zones is approximately level with the open water 
of the lake. During the hottest and driest months of the summer 
the water supply is greatly reduced by a lowering of the water 
table, and when water is removed by the surface layers, it is very 
slowly replaced by that of the deeper parts. It is only in these 
surface layers that these plants root. In any bog where a clearing 
of any extent has been made, one finds areas where the tamaracks 
have been blown over during storms; these show that even the 
largest trees root in the surface layers only. 
It has been shown in fig. 7 that the water table in the various 
parts of the bog stood at different heights during the summer. 
This is the controlling factor which makes the bogs in this region 
heterogeneous habitats, supporting xerophytes in three zones 
and hydrophytes or mesophytes in other zones. 
The first effect of lowering the water table, as has been pointed 
out, is to make the habitat xerophytic, and one would expect that 
those areas where the water table is lowest would be most xero- 
phytic. A glance at the plants shows that this is not the case; 
the outer zone in this lake is occupied by hydrophytes. This is 
due to secondary changes. Immediately after the water lowers, 
a number of other changes set in which produce the opposite 
