MICHIGAN ACADEMY OF SCIENCE. 
173 
RESULTS OF THE MERSHON EXPEDITION TO THE CHARITY 
ISLANDS, LAKE HURON. 
PLANTS. 
C. K. DODGE. 
The Charity Islands are situated in Saginaw Bay, a part of Lake 
Huron, about nine and one-half miles from Caseville in Huron County. 
The group consists of three islands known as Charity, Little Charity 
and Gull Islands. Charity Island, which has for a long time been owned 
and used for light house purposes by the United States Government, 
contains about 650 acres and is much longer in the north and south di- 
rection than wide. Little Charity is the next largest island and is 
privately owned and used as a fishing station. It is about 3 acres 
in extent and nearly round in shape. Gull Island is a small projecting 
reef and was not visited in the course of this work. 
The writer visited the islands in 190S, 1909, and in 1910 with the 
Mershon Expedition, and thoroughly examined the flora. 
It is very evident that since the glacial times these islands have not 
been connected with the mainland. The islands themselves have been 
formed by the accumulation of sand upon the rocky reefs that were 
exposed at these places when the level of Lake Huron was lowered. It 
is evident that the islands are still in the course of formation, for at 
the north end of Charity Island there is a submerged bar extending 
far out into the lake, and at the south end, the water is very shallow for 
a considerable distance out from shore. On Charity Island exposed rock 
is now mostly to be seen at the north end. but it is also exposed in some 
places on the east and west sides; the sand has been blown up 
into ridges on the shore and the island is for the most part made up of 
low and nearly parallel sand ridges running in a northerly and south- 
erly direction. In their formation these ridges probably occasionally 
enclosed lagoons, as they did on the mainland. There is a lagoon (“the 
pond”) at present on the southern end and west side of Charity Island. 
Between the ridges many low places have become partially filled and 
partly owing to the collected humus form rich damp soil. It will thus 
be seen that the three major types of habitats, hydrophytic, mesophytic, 
and xerophvtic are found here. 
At the present time the islands are densely covered with trees, shrubs 
and herbaceous plants. On Charity Island only a small area has ever 
been cultivated and no stock, except a few swine, has been allowed to 
roam. The vegetation is thus in a virgin condition. As would be ex- 
pected, the plant covering is composed of mainland species. But the flora 
as a whole shows the influence of its isolation. The seeds of nearly 
all of the forms now found on the islands must in one way or another 
have been carried across the water from the mainland. As one would 
expect those plants that have seeds adapted for transportation by wind 
