146 Knight and Priestley . — The Respiration of Plants 
identical with that described above, except in the form of the respiration 
chamber employed, which consisted of two bell-jars with ground flanges 
fitted together and rendered airtight with a vaseline-rubber composition. 
Each bell-jar was stoppered with a rubber stopper through which passed 
a delivery-tube and a platinum-mercury electrode. (See Fig. 1.) The 
platinum wire of the lower electrode was attached to a disc of wire 
gauze on which the seeds rested, thereby ensuring good contact, whilst 
the mercury was ‘ earthed ' by means of a wire connected to a water-pipe. 
The upper electrode was connected to the positive pole of the discharge 
apparatus by means of a rubber insulated cable running through quartz 
tubes borne on porcelain telegraph insulators. 
The air-stream entered the chamber through the upper delivery-tube, 
and left it through the lower. 
In the early experiments the source of electricity was a large influence 
machine kept running by a motor, but later the Lodge-Newman installation 
was used. This was much more satisfactory, the electrical output of the 
influence machine being very variable, and to some extent at the mercy of 
the weather. 
It will be convenient to describe first the series of control experiments 
which were carried out under different conditions, as it is only in the light 
of these control experiments that experiments with the electric discharge 
can be interpreted. 
1. Seeds were packed into the lower of the two bell-jars, and the curve 
of respiration determined as in the low tension current experiments, with the 
result that it was found impossible to depend upon obtaining a smooth normal 
curve every time. The irregularities were sometimes in one direction and some- 
times in another, and it was thought to be due to the fact that the close 
packing of the seeds prevented efficient aeration, the respiration being thus 
rendered partially anaerobic (Table III). In view of later observations, 
however, it seems likely that at least some of the irregularities were due to 
temperature variations, which were not recorded. 
2 . The seeds were separated from each other by layers of glass wool 
to ensure proper aeration, and the normal curve was again determined. 
The irregularities here were much less marked, and accordingly glass wool 
was always used in subsequent experiments (Table IV). 
3. Electric discharge from a point in air causes the interaction of the 
gases of the air, with the formation of oxides of nitrogen and ozone, and 
probably, if water vapour is present, a little hydrogen peroxide. 
Owing to misinterpretations of some of our results, coupled with some 
conclusions arrived at by Hill and Flack, 1 who found that very small quanti- 
ties of ozone were toxic to animals, it was thought that these gases 
had a deleterious effect upon the plants, and steps were taken to prevent 
1 Proc. Roy. Soc., 84 B., 1911, p. 404. 
