n8 M. J. Lynn 
resulted when carbon dioxide was present in certain quantities in 
the atmosphere. 
It was some time before the best method of procedure was arrived 
at, and since these preliminary experiments were conducted on less 
accurate lines, they will not be referred to further in spite of the fact 
that the results were in accordance with the theory. 
It was found, in the course of preliminary experiments, that the 
seedlings which gave the best results were those of Helianthus annuus ,' 
because they respond so readily to the stimulus of gravity under 
normal conditions, and because they are even more ready to show 
an abnormal curvature under abnormal conditions. 
The following method was the one adopted in all the experiments 
tabulated below: A box containing sand in which were growing a 
number of erect, healthy seedlings of Helianthus was fixed in a large 
bell-jar so that the hypocotyls were in a horizontal position. (The 
bell-jars used in the experiments varied in volume from 4000 c.cs. up 
to 9000 c.cs.) A ground glass plate was sealed to the bottom of the 
jar with paraffin wax and carbon dioxide was introduced by dis¬ 
placement of a known volume of water, giving a percentage which 
was known approximately. The jar containing the seedlings was 
placed in a dark cupboard, in order to avoid heliotropic effects, and 
was examined at regular intervals. One of the properties of carbon 
dioxide is that it diffuses rapidly and, this being so, it may be 
taken that the gas in the jar was of uniform concentration through¬ 
out. Samples of gas from the top and bottom of a jar were analysed 
and proved to contain the same percentage of carbon dioxide. Further, 
as soon as a curvature in any direction was noticed, a sample of the 
gas in the jar was analysed. The apparatus used in the analysis of 
the gas in each case was a modification of the Hempel Apparatus 
for Gas Analysis. 
The experiments' carried out are tabulated below, and in each 
case the method adopted was exactly similar to that described above. 
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