108 BOTANICAL GAZETTE [AUGUST 
The flora of the postglacial lakes studied in southern Michigan 
may be classified thus: 
: Submerged plants 
sarorper Water lilies 
Floating sedges 
Xerophytes } Bog shrubs 
Tamaracks 
Vegetation in postglacial 
lakes 
Hydrophytes or 
tnesophytes 1 Poplar-maples 
Hydrophytes Marginal willows 
An investigation has been carried on for several years by the 
author and some of his advanced students to determine as far as 
possible the edaphic conditions in the different areas outlined 
above. A short report has been given (5) and a more detailed 
account of some of the results is given in this paper." 
Temperature 
The aerial parts of the bog plants are subjected to great extremes 
in temperature. Situated, as they are in the area under discussion, 
in low basins with often very steep sides, the air from the adjacent 
uplands drains into them, producing a temperature several degrees 
lower than that on the surrounding uplands during the night and 
early morning. During the day, however, very high temperatures 
have been recorded. Such temperatures have also been recorded 
by GANONG (10, 11) in New Brunswick. 
Unless otherwise stated in the text, all temperature readings 
given in this paper, both for soil and air, were taken with Richard 
Fréres, Paris, thermographs belonging to the University of 
Michigan. These instruments are shown in fig. 2 in the shelter 
in which they were kept in the field. The one on the left records 
the air, the other the soil temperatures. It was found, unfortu- 
nately, that the soil thermometer was unreliable when the tempera- 
* Bog conditions in southern Michigan, rai lies toward the southern limit of 
their distribution in this country, seem to be quite different from bog ae 
farther north described by GANONG (11). i point was emphasized also b 
TRANSEAU (17, 18). See also BAstrIn and Davis (1). 
