38 Leitch. — Some Experiments on the Influence of 
period while the temperature rises from about 33 0 to 40°, and they give 
a value of 0-50 in ten minutes, which is more than twice as high as the value 
in the first ten minutes at 40°. 
At 42*7° the fall is similar but steeper. At temperatures between 
44'5° and 45 0 , growth can no longer take place. A slight increase in length 
takes place during the raising of the temperature, but in no case is there any 
after the temperature has reached 44*5°, and usually contraction occurs 
immediately. To quote an illustrative experiment : 
Readings at one-minute intervals for ten minutes ; then two readings, one after five minutes and 
one after thirty more minutes : 
'Temperature. 39 0 , 41-8°, 42-8°, 43-8°, 44*1°, 44-3°, 44-5°, 44-8°, 44-8°, 44-8°, 44-8°, 44-9°, 44-9° 
Growth . O'l 000 —o*i 0000 —o*i — o*2 —0*5 
In this time, forty-five minutes, the root had contracted 0-45 mm., had, 
as was typical, become discoloured and flaccid and, left at room temperature 
for two days, showed no sign of recovery. The death-point appears there- 
fore to lie below 45 0 . 
It must be borne in mind however that, with regard to this, the death- 
point itself is dependent on time. All roots after a shorter or longer 
exposure to temperatures above 30° became flaccid and discoloured, the 
normal colour of the root changing to a dull white, and the greeny-yellow of 
the root-tip to a dull brown. At 35 0 this required several hours ; but, 
while all roots left overnight at 35 0 were killed, the shoots recommenced to 
grow at room temperature and continued quite vigorously during the next 
two days. At 40° growth had stopped in most roots after an hour, and in 
none did it continue after one and a half hours. In two hours the roots were 
flaccid and discoloured, and neither the roots nor the shoots showed recovery 
in the next two days. At 427 0 growth occurred only in the first half-hour, 
and after one hour there was no recovery. At or below 45 0 , death seemed 
to be instantaneous. 
Discussion of Results. 
Considering the results first from the point of view of Blackman’s 
theory, it appears at once that no extrapolation according to Blackman’s 
method is possible. Even if there were not the sudden drop and recovery 
at 30° and 35 0 , the rate during the raising of the temperature from 30° to 
35 0 shows that the rate at 35 0 never does rise above that in the first ten 
minutes at 30°. It is even more evident that the rate at 40° never does 
exceed that at 30° or 35 0 . Again, the coefficients for a rise of temperature 
of ten degrees are : 10/0 — 8-25, 15/5 = 4-07, 20/10 = 2*90, 25/15 = 2*38, 
29/19 — a value probably greater than 2. They show a very distinct fall 
as the temperature rises ; only between io° and 29 0 do they lie between 
