1 38 Knight and Priestley . — The Respiration of Plants 
The foregoing data indicate that the acceleration effect occurs sufficiently 
frequently to be worth analysis, but a further study of the method of 
carrying out a field experiment has thrown a considerable amount of doubt 
upon the conclusions they have so far suggested. 
When the distribution of the electric discharge from an overhead 
system of wires is studied by electrical methods, it soon becomes clear that 
any electrical effect produced will not be restricted to an area of ground 
just beneath the wires. On the contrary, when the slope of electric 
potential is mapped over the field, the effect of the discharge is seen to 
spread a number of yards on all sides of the outer wires, and when a wind 
is blowing the current is carried a very long distance down the wind . 1 
Thus, when the matter is investigated, it may happen that a point on 
the control, as far removed as possible from the overhead wires, may be 
receiving about one-tenth the current per unit area that the ground directly 
beneath the overhead wires is receiving, while a proper control, obtaining 
only the normal atmospheric discharge, would receive at most a current 
that was ten thousand times less than that under the wires. Under such 
conditions it is clear that the control plot fails in its object. An attempt is 
now being made in the field (at Lincluden Mains, Dumfries) to determine 
the question as to whether acceleration really takes place under more 
rigorous experimental conditions, i. e. with a control as carefully screened 
from additional electric discharge as is practically possible. 
It is perhaps worth pointing out that the most consistent reports as to 
acceleration have come from the Evesham experiments, where the areas 
have been large and where it is at any rate probable that the control area 
has to some extent been under normal conditions . 2 
Until some physiological analysis of the effect of electrification upon 
the katabolic and anabolic processes of the plant has been carried out, it is 
not possible definitely to attribute the increased yield to direct effect upon 
any single process in the plant. 
The result of an investigation of the effect of electrical stimulation 
upon carbon dioxide output is given in the following pages, and although, 
under the conditions obtaining in our experiments, we have been able to 
record a distinct increase in carbon dioxide output during electrification, 
we have found that this increase can be wholly attributed to a rise of 
temperature, which takes place owing to the production of heat during the 
discharge. Thus we are led to conclude that the explanation of the 
acceleration phenomena recorded above is not to be found in the response 
of the respiratory function of the plant to electrification. 
1 This is especially marked in recent experiments where the overhead wires are from 10 to 15 
feet above the ground. 
2 For a fuller discussion of this question see paper in the Journal of the Board of Agriculture, 
vol. xx, p. 582. 
