132 BOTANICAL GAZETTE [AUGUST 
importance is in its effect upon the functional activities of roots 
and rhizomes. Recently the temperature of soils and its fluctu- 
ations have received considerable attention. The relationship, 
however, and the general effect upon plant forms and the corre- 
lated functioning are nevertheless but little understood. This 
circumstance is perhaps the more to be regretted, since, broadly 
speaking, it seems that the relationship to plant life is the more 
favorable the more dominating the influence of the physical char- 
acters of the soil and particularly the relations prevailing in regard 
to the physiological water content and efficient temperature. 
THE ROLE OF SUBSTRATUM TEMPERATURE IN BOG HABITATS 
During the first few months of field work the device chosen for 
obtaining the substratum temperatures was the ‘“thermophone.” 
The apparatus is based upon the principle that the resistance of 
an electric conductor changes with its temperature. In obtaining 
the temperature of peat soils at various depths, the coils were 
sunk to the required depth, and their leading wires were then con- 
nected with the respective binding posts of the indicator box. 
A buzzing sound in the telephone increases or diminishes accord- 
ing to the position of the pointer while receding from or approach- 
ing to a section of the graded dial. Hence the position is soon 
found where the telephone is silent. This point indicates the 
temperature of the sunken soil. The instrument is very sensi- 
tive, but very inconvenient for obtaining weekly and monthly 
minimum and maximum temperatures. Later in the season the 
investigations were planned for a set of thermographs such as 
MacDoveat described (25), that would make a continuous record 
of the temperatures at any desired depth. The lack of sufficient 
funds and the failure to secure similar instruments made it neces- 
sary to resort to a conventional though less graphic method of 
measuring the temperature exposure of plants. In the field work 
of 1908, 1909, and at present, mercurial minimum and maximum 
thermometers were therefore used. The thermometers for the 
deeper peat strata were fastened to wooden poles and pushed down 
into the soil to the depth of 5 feet (1.5 m.). They remained in 
the soil during the period of investigation except for such short 
