MICHIGAN ACADEMY OF SCIENCE. 
57 
The zone of water plants consists chiefly of Scirpus lacustris, Pon- 
tederia cordata, and large quantities of Nvmphaea adyena, which grow 
in the water and loose peat just in front of the sedge mat. 
FACTORS DETERMINING DISTRIBUTION. 
A considerable amount of discussion has been carried on about the 
historical factor 1 in the distribution of bog plants. In such work as 
the writer attempted, however, particular attention was paid to local 
factors, and the historical factor can be ignored. 
A straight line, beginning at the northeast side and running south 
by southwest, was laid out across the bog in such a way as to cross 
all the zones mentioned above. (Fig. 2 AB.) To correlate the depth 
to the present distribution, borings were made every hundred feet to 
determine the depth and, in a general way, the nature of the deposits. 
All parts of the bog and the lake which have a depth of more than eig'ht 
feet are underlaid with marl, which forms beds often sixteen to twenty- 
five feet in thickness. To determine accurately the relative position, 
size, and frequency of the plants and the relation of the societies to 
each other, a plot was made for a strip forty to fifty feet wide along 
this line. 
Beginning at the north end the line first crosses a marshy meadow, 
which is one hundred fifty feet wide at this point. The peat is very 
dark and has a maximum depth of eight feet. The owner said that 
previous to the last fire he had mowed this meadow annually for marsh 
hay, but that since that time he had been unable to mow it at all be¬ 
cause the surface is too uneven. He affirmed that the peat was burned 
to a depth of six feet in some places. The higher parts of this meadow, 
where it was burned the least, are now covered with marsh grasses and 
a few sedges; lower places are filled with wet-soil sedges, blue flags, 
sensitive ferns, and cowslips; and still lower places, which are seldom 
free from open water, contain water-plantains and cat-tails. 
In the next two hundred feet the depth increases from eight to thirty- 
five feet. The peat becomes lighter as the depth increases. At the place 
of greatest depth, it is a yellowish brown and rests upon ten to twelve 
feet of marl. Evidently this area was once covered with tamaracks, 
which have been nearly all burned off. At the present time the first one 
hundred feet on the land side is covered with willows, and the rest of 
it on the bog side with Populus tremuloides. Very many other plants 
are found growing with the willows and with Populus tremuloides. 
Of thirty species listed for the willow society at this point, only eight 
species are characteristic of bog flora; of twenty-eight species listed 
with the Poplars, fifteen are characteristic of the bog. Almost exactly 
as the depth increases from ten to thirty-five feet, the Populus tremu¬ 
loides decrease in size and numbers, and are replaced by a Sphagnum- 
Cassandra society. This society extends four hundred fifty feet across 
a basin twenty to thirty feet deep. Beyond this is another burned area 
very similar to the first Poplar area except that Poplars have not 
grown so large, young tamaracks are more common, and the number 
of mineral soil species is much less. Abruptly following this burned 
'Transeau, Bot. Gaz. 40, p. 351. 
8 
