28 Leitch. — Some Experiments on the Influence of 
root-tip had been between the 14 and 15 mm. lines, it would also be called 
15 mm. 
The experiments were carried out in a gas thermostat, where it was 
possible to vary the temperature from n° upwards. The temperature was 
recorded by thermograph tracings, and even at the highest temperatures 
used the fluctuations shown did not exceed 0-5°. Temperatures below n° 
were obtained according to the weather in a room of very constant tempera- 
ture, where a thermograph tracing was a straight line for days if the windows 
were undisturbed and the door kept closed. Temperatures near to and 
below zero were obtained in the open air. The lowest was in an experi- 
ment where the temperature did not rise above — 2 0 and where the minimum 
Text-fig. 3. Temperature in 0 C. 
was — 5 0 . Here no growth took place ; instead, a slight general contraction. 
The roots were frozen, but, on thawing at room temperature, continued 
to grow. 
It was intended that the experiments should be in two series ; the first 
was completed, and in the second— which began about 15 0 — for some cause 
which I have been quite unable to explain, the values of the growth-rate 
suddenly rose and maintained a level uniformly above those of the first 
series to 28°, after which the usual fall of the rate took place, that is to say, 
at a temperature which is about two degrees lower than in the first series. 
At this point, in view of these results, the number of peas soaked each day 
