148 Knight and Priestley . — The Respiration of Plants 
of the short xylol resistance is the fact that sparks are liable to penetrate 
the glass tube and pass down the side of the respiration chamber, incident- 
ally allowing the xylol to escape on to the seeds. Although quartz 
electrodes were tried instead of glass ones, this difficulty was never entirely 
obviated. A series of experiments was carried out using different current 
densities, but owing to the obstacle mentioned we were unable to get any 
current densities above 3 x io -6 amperes, except that obtained with a mercury- 
platinum contact electrode, namely about 5 or 6 x io~ 6 amperes. 
The method of procedure in these discharge trials was the same as that 
described for the direct-current experiments, i. e. the seeds were introduced 
into the respiration vessel and maintained under normal conditions for 
a time, determinations of carbon dioxide output being made every half- 
hour. These values gave an indication of the trend of the normal curve for 
the particular set of seeds under observation, and the discharge was switched 
on usually during the fifth half-hour from the start, two or three determina- 
tions being made after the return to the unelectrified condition. 
The results of these experiments are given in full in the Appendix, and 
it will be seen that discharge producing a current density of less than about 
3 x io~ 6 amperes has no effect upon the respiration of the seeds, the normal 
curve being uninterrupted at any point. When, however, a current density 
of 3 x io~ 6 amperes was reached there was a definite irregularity in the curve 
(see Fig. 4). The irregularity consists of a rise which takes place, not 
during the period of electrification, but during the half-hour following it. 
Sometimes the rise is very slight, and in one case (No. 90) there was no 
actual rise, but the slope of the curve was diminished, indicating that the 
carbon dioxide output was nevertheless greater, consequent upon electrifica- 
tion, than it otherwise would have been. The magnitude of this general 
