54 
EIGHTH REPORT. 
PLANT DISTRIBUTION AT MUD LAKE.* 
L. H. PENNINGTON. 
Mud Lake is one of Michigan’s numerous post glacial lakes. It is 
located about eleven miles northeast of Ann Arbor, and was at one time 
an arm of Independence Lake. Now, however, it is almost entirely filled 
with marl and peat deposits, the only open water being a strip about 
(60) sixty rods long and (20) twenty rods wide at its widest part. A 
glance at the map (Fig. 1) shows that the peat-forming plants have 
first come into the irregular arms of the old lake and made its margin 
very regular as compared to the original shore. Of the several arms 
Mud Lake presents the most interesting and instructive field of study, 
because it shows all stages in bog formation from open water to the 
spruce-tamarack forest and the marsh-meadow. Plant succession may 
be studied here under natural conditions as well as under changed con¬ 
ditions due to clearing and to burns. Many of the tamaracks have 
been taken away for fuel or fence posts, loads of spruces have been cut 
annually for Christmas trees, and severe fires, fifty years ago and again 
eighteen years ago, burned over large areas. 
It is customary to group plants into various societies. For conven¬ 
ience we may divide the plants within and around the bog into two 
large groups of societies; first, the mineral soil societies, and second, 
the peat bog societies. Although some plants are common to both 
groups, and in some places the societies of one group merge into the 
societies of the other group so gradually that it is hard to draw a line 
between them, yet, as a rule, the plants are very different for the two 
groups and live under very different conditions. ' 
The plants of the first group may be considered with respect to the 
three habitats in which they are found. These habitats are, first, the 
well-drained hills, covered with an oak-hickory society; second, the low 
ground or the level, poorly drained soil, covered with a white ash-beech- 
maple society or by an elm-black ash-swamp.oak society; third, the old 
lake shore, covered by a great variety of species, due partly to the fact 
that within the space of a few feet there may be xerophytic, mesophytic, 
and hydrophytic conditions, and partly to "the fact that this strip in 
many places has been changed but little by cultivation. Thus many 
introduced plants, commonly 7 called weeds, as well as many native 
plants, grasses, sedges, composites, etc., become established here. 
The peat bog societies were studied in detail. Writers have classified 
peat bog plants in various ways. Five principal zones will be taken up 
here; first, the zone of marginal plants; second, the zone of tamaracks 
* Contribution 90 from the Botanical Laboratory of the University of Michigan, 
George P Bum? d ° ne in the summer of 1905 under the direction and with the assistance of Dr. 
