1910. | On Vegetable Assumilation and Respiration. 381 
This form of valve has worked quite smoothly and the gas given off passes, 
with an occasional drop of water, intermittently into the receiver Z. From 
here by turning tap f and raising the mercury reservoir the gas can be driven 
through the side tube into a eudiometer for analysis. 
From the shrinkage in volume of the gas after treatment with KHO in 
the eudiometer the absolute amount of gaseous COs physically liberated from 
the water-current during the time since the last analysis is determined : this 
is used as a correction to obtain the proper assimilation. 
Section [].—THE APPLICATION OF THE METHOD. 
(a) Procedure in a Typical Experiment.—As an example of the method 
pursued in carrying out an experiment, and the calculation involved in 
arriving at the real assimilation, we propose now to describe a single case in 
detail. We select the first experiment done in 1907 when the apparatus had 
taken on the final form just described. The object of this experiment was to 
determine the assimilation by Elodea with an illumination equal to 5:7, at a 
temperature about 20° C., and a COz-supply of about 0°03 grm. per cent. 
(about one-sixth saturated). 
The Elodea was gathered at 9.45 a.M. on June 7th in a stream about a mile 
from the laboratory, brought back in a tin and placed at once in tap-water. 
The first proceeding is to set up the material in the assimilation chamber.* 
Only the greenest and healthiest shoots were selected from the gathering, 
and these were laid down one by one on the silver grid until a continuous 
dense green layer, without any gaps, was formed on the front side of the 
grid. The whole was secured with cotton, the grid slipped into the chamber 
(its four projecting pegs fitting into slots in the iron frame), and the front 
glass, which had been carefully cleaned since the previous experiment, was 
again waxed on. 
To accomplish this the glass was pressed down on to the film of wax left 
on the metal frame, and then lumps of wax-mixture were placed round the 
edge at intervals. These were melted and run uniformly round with a tiny 
gas-flame from a capillary tube at the end of a length of flexible tubing, the 
the junction being waxed over watertight. The drum can, therefore, be easily opened 
for inspection and adjustment. The strip of oil silk emerges through fine slits in the 
roof, which are also closed by wax. 
* At the end of each experiment the chamber is opened by taking off the front glass, 
wiped and left to dry ; the silver grid is removed, and the plant carefully taken off and 
spread out to dry up quickly in the air in order to obtain its dry weight. The bent 
glass inlet tube below, 6, and the valve-drum Y above are never detached from the 
chamber. The widened lower end of the tube of the drum just slides over the metal 
outlet tube of the chamber, and so makes a rigid joint which indiarubber tube renders 
watertight (see large scale drawing at top of fig. 1). 
