50 
JOHN H. EHLERS 
Table III 
Comparison of Junctions 
Date 
Temperature 
Displacement in Cm. 
Diff. in Mm. 
A 
B 
Diff. 
Junct. No. I 
Junct. No. 2 
Jan. 3 
22.85° 
20.42° 
2.43° 
21.0 
20.9 
I 
22.90 
20.42 
2.48 
21.5 
21.4 
I 
23.04 
20.48 
2.56 
22.2 
22.1 
I 
24.10 
20.53 
3.57 
31.0 
31.0 
0 
24.10 
20.53 
3.57 
31.0 
31.0 
0 
24.09 
20.55 
3.54 
30.8 
30.7 
I 
25.60 
20.56 
5.04 
43.7 
43-5 
2 
25.57 
20.57 
5.00 
43-4 
43.4 
0 
26.58 
20.56 
6.02 
52.3 
52.3 
0 
Jan. 4 
26.55 
20.60 
5-95 
51.9 
51.8 
I 
20.28 
19.24 
1.04 
9.0 
9.0 
0 
19.60 
19.21 
.39 
3.4 
3.3 
I 
1945 
19.15 
.30 
2.7 
2.6 
I 
19.50 
19.17 
.33 
2.9 
2.9 
0 
29.80 
19.04 
10.76 
93.2 
93-2 
0 
29.78 
19.04 
10.74 
93.1 
93.0 
I 
(2) The Formation of Secondary Couples. — Any difference in the 
composition of the metals at the connections, or any sHght difference 
in the composition of the metal in the wires themselves may, if there 
is a difference in temperature at those points, cause the formation of 
secondary couples. For the purpose of this investigation the latter 
case may be neglected, as the error arising from this source would be 
exceedingly small. To guard against secondary couples at the 
connection of the lead wires with the heavy copper wires, copper 
binding posts were used and the joints placed as closely together as 
practicable to insure the same temperature for both. The connections 
with the apparatus in the laboratory were all under uniform tempera- 
ture conditions throughout the experiments and, consequently, the 
danger from secondary couples at those points was reduced to a 
minimum. 
(3) Heat Due to the Wounding of the Leaf Tissue. — ^The develop- 
ment of heat in wounded tissue is due to an increased respiration of 
the injured part. Tiessen (30) found that the rise in temperature due 
to wounding increases with the extent of the wound ; that its duration 
varies from one half to three days; and that its absolute value varies 
from 0.02° to 0.08° C. with an average of 0.04° C. Richards (22) has 
shown that a curve plotted for the heat developed in wounded tissue 
corresponds in the main to that of the respiration intensity under the 
