8io 
Irving.—Photosynthesis and 
baryta solution. The current was moved consecutively from one tube to 
another by clockwork at intervals of two hours. 
The tubes which had been used were removed, titrated, and refilled, 
at convenient times. 
The method used for titration was to wash out the contents of the 
tubes with a constant amount of boiled distilled water into a beaker and 
titrate with N/io HC 1 , using phenolpthalein as an indicator. The tubes 
were then refilled with baryta solution, and replaced in the stand. Con¬ 
tamination of C 0 2 from the atmosphere during washing, titrating, and 
refilling was allowed for by a small ‘ washing factor ’ obtained from a number 
of controls carried out for that purpose. 
As the temperatures of all the experiments, with one exception, were 
approximately constant the readings are directly comparable. 
Before proceeding to experimental data it is necessary to consider 
what would happen to the respiration of a shoot or leaf, if it were cut off 
from its source of food material, and kept continuously in the dark. 
In such a starved condition there is always a considerable fluctuation in 
the successive respiration readings when these are of such short periods as 
one or two hours, however constant the temperature may be kept; more 
especially is this the case when the organ is at first placed under the experi¬ 
mental conditions. Nevertheless, there is a general broad regularity under- 
4 lying these fluctuations, according to which the respiration remains at 
a uniform average level for the first few hours (the exact time depending 
on the temperature), and then begins to fall in a regular curve, at first 
rather rapidly, and then slower and slower towards a lessened uniform value. 
The different experiments all illustrate this, as well as the general 
truth that, the higher the temperature, the steeper is this curve of declining 
respiration. 
Experiment III. 
We may take first an experiment made with etiolated Barley seedlings. 
The plants were germinated in the dark, and when the first foliage shoots 
were about 6 inches high, the shoot was cut off at the level of the soil. 
Enough of these shoots were placed vertically upright in the chamber to 
make a continuous layer of deep yellow etiolated leaf material. They 
were kept in position by being lightly held by the two glass plates of the 
chamber, there being water in the bottom of the chamber to moisten the air. 
The chamber was set up on its stand and placed in the bath, regulated 
to a temperature of 25-2° C. facing the window, and the current of C 0 2 -free 
air started through it, with the bath carefully darkened. 
After a preliminary of two hours a continuous series of twenty-one two- 
hour estimations of the respiration was carried out. Table I records the re¬ 
sults ; and in the last column are inserted notes of the colour that was 
