34 Leitch. — Some Experiments on the Influence of 
mined, the rate of growth, under the conditions of experimentation, is 
actually constant during the whole of the third day at very low temperatures 
and at 25 0 for at least six hours. Since, therefore, all points on the curve 
of growth are means of readings taken over usually three half-hours (some- 
times one or two ; never more than six), it may be taken that the difference 
between readings at different temperatures is entirely due to the difference 
between the temperatures. On the other hand, in the long-period experi- 
ments there will probably be a slight disturbance due to the passing of the 
Grand Period during the time of the experiment. 
At the commencement of the microscope experiments, I decided that 
most time should be devoted to low temperatures and to high, because, 
on the one hand, I thought that there might be a possible inaccuracy in the 
long-period determinations at low temperatures due to the length of time 
necessary for the apparatus to sink from the temperature of the laboratory, 
at which measurements were made, to the temperature of the experimental 
tion room or the open air ; and, on the other hand, the long-period method 
is impossible as a means of accurate analysis at high temperatures. The 
number of experiments at low and at high temperatures is therefore 
much greater than at medium temperatures, but the agreement of the 
determinations at medium temperatures shows them to be sufficient. 
At low temperatures it was found that the new results agreed with the long- 
period experiments: but already at about io° the two curves diverge, and 
separate more and more rapidly to 29 0 . An analysis of the reasons for this 
has not been possible, but two things are probable, (1) that the Grand 
Period affects the long-period experiments to some extent, and (2) that the 
difference in the conditions of experimentation accounts for a considerable 
part of the difference. At least at temperatures above 20°, preliminary 
experiments, before the method described for the microscope experiments 
was determined upon, showed that the question of sufficient moisture 
is of the greatest importance, and that devices such as lining the tube with 
moist filter-paper (perhaps comparable to, though not so good as, the con- 
ditions in the long-period experiments) were quite insufficient to supply the 
roots with the necessary moisture. With the more perfect water-supply 
a higher rate of growth is to be expected, and was found. 
The experiments from o° to 20° were in one series, those from 20° to 
28° in two series, and for higher temperatures the experiments were in 
several series. This precaution was adopted to prevent any possibility 
of disturbance through the operation of a particular set of conditions, 
as occurred in the experiments of Series I. No indication of any such 
appeared ; control experiments, repeated during the experiments at high 
temperatures to make sure of the good condition of the roots, always gave 
results agreeing exactly. The experiment at 25 0 quoted in connexion with 
the question of ‘temporary stimulation’ by a rise of temperature (Expt. 
