under Various Electrical Conditions . 
145 
rise in the temperature of the seeds quite independent of the temperature 
changes of the laboratory, and this rise was found to correspond with that 
which was to be expected from a calculation from current strength . 1 
This rise of temperature has probably been an important factor in 
many of the results recorded in the field experiments, more especially where 
comparatively large direct currents through the soil have been employed. 
Lowenherz 2 describes a rise of temperature observed in some experiments 
on the effect of direct currents upon the growth of barley, and suggests that 
the acceleration of growth which was recorded may have been due to this 
rise of temperature. 
In the course of our direct-current experiments, doubts arose as to 
what proportions of the current measured actually passed through the peas 
and their water films respectively, and rough experiments were made to 
ascertain the relative conductivities of the water and the seeds. The con- 
ductivity of the respiration tube filled with water in which seeds had been 
soaked was first determined, and then seeds were packed in, the interstices 
between them being filled with water, and the conductivity was again deter- 
mined. The presence of the seeds lowered the conductivity in the ratio of 
2 : 1. Peas packed in a tube such as that used occupy only about one-half 
its volume, so that by the introduction of the seeds the area of the cross- 
section of the original conducting medium, water, has been reduced by 
about one-half, and incidentally the conductivity has been reduced in 
a similar ratio. From this it appears that the seeds themselves have a very 
high resistance, and consequently, in the ordinary low tension current 
experiment, by far the greater part of the measured current must pass 
through the water films on the seeds. 
Thus we were unable to show any alteration of the katabolic processes 
of germinating seeds when subjected to minute low tension direct currents, 
but it was not possible to determine the exact current strengths in the seeds 
themselves. With low tension currents, then, unless the current is sufficiently 
strong to raise the temperature of the plant or its surroundings, no increase 
in the plant’s respiration is to be expected. With high tension currents, no 
experiments have been carried out with currents greater than from 10- 13 to 
10- 11 amp. per sq. cm. ; but no direct deductions can be drawn from this 
fact, as with the higher tension the distribution of the current in the plant 
may be very different. 
2. Experiments with High Tension Discharge. 
These trials were carried out chiefly with germinating peas, although 
a number of experiments were made upon seedlings. The method used was 
1 But this calculation was based upon the formula for the heating effect of a current passing 
through a conductor. If the seeds behave as an electrolyte to the passage of the currents this 
calculation will not apply. 2 Zeitschr. f. Pflanzenkrankheiten, vol. xviii, 1908, p. 336. 
L 
