152 Knight and Priestley. — The Respiration of Plants 
A suggestion presented itself to the effect that the rise of temperature 
so constantly observed might be the result, and not the cause of the 
acceleration of the katabolic processes accompanying it, but this explana- 
tion was confuted by experiments upon the electrification of dead peas 
(Table XIV). In this case it was found that there was again a rise of 
temperature, whereas there was certainly no acceleration of the katabolic 
processes, the conclusion being that the increased carbon dioxide output in 
the experiments upon living seeds was indeed due to the temperature rise. 
Some experiments were also carried out upon the effect of the electric 
discharge upon the respiration of seedlings. The plants used included 
peas, brussels sprouts, wheat, and rye, the two last proving the more satis- 
factory, on account of their more rapid germination and larger evolution of 
carbon dioxide per unit space occupied. 
The seeds were planted in sand in the lower bell-jar of the apparatus 
described on pp. 145 and 146, and the delivery-tube for the exit of the air- 
stream was made to reach the surface of the sand. The second hole through 
the stopper was left open for drainage purposes whilst the plants were 
growing, and was later used for the ‘ earthed ’ electrode, which merely made 
contact with the sand which was penetrated by the roots of the plants. 
When the plants had grown to a convenient height, the upper bell-jar 
was waxed on and the whole chamber covered with thick brown paper to pre- 
vent access to light, thus precluding the possibility of photosynthesis taking 
place, and control experiments were carried out under these conditions. 
The carbon dioxide output was measured for several consecutive 
periods without any electrification, and it was found that the respiration, as 
in the case of the seeds, gradually decreased as the experiment proceeded, 
but with the seedlings the variation was never more than 5 per cent, after 
corrections had been made as usual to compensate for temperature changes 
(Table XV). 
Accordingly, instead of finding a normal curve in each experiment, as 
in the case of seeds, it was considered permissible to measure the carbon 
dioxide evolved during two successive periods, the discharge being switched 
on at the beginning of the second. The length of each period was usually 
one hour, sometimes two, a convenient quantity of carbon dioxide being 
produced in this time. In the results, differences of less than 5 per cent, 
were disregarded as insignificant in view of the information obtained from 
controls. 
A series of experiments was carried out under these conditions, 
employing current densities up to io~ 6 amperes, which were obtained by 
means of the xylol resistance previously described. Above this strength no 
results were obtained, owing to the failure of the xylol to withstand the 
heat produced (see p. 147). 
In no case was it possible to record any significant variation of the 
