Temperature on the Rate of Growth in Pisum sativum . 35 
No. 7) was the last experiment done, and it shows conclusively that no 
alteration or disturbance in the material had occurred, for the value it gives 
lies exactly on the growth-rate temperature curve. Table III gives the 
results from o° to 29 0 , and Text-fig. 6 shows the relation of growth to 
temperature in graphical form. Up to and including 28°, the growth-rate 
is constant during the time of the experiment. 
At temperatures between 28° and 30° a new factor comes into opera- 
tion. At this point, experimentation becomes very difficult. On raising 
the temperature to about 29 0 , in most cases rapid and sharp curvatures took 
place. These curvatures are not the gentle curvatures already referred to, 
extending over perhaps half the length of the root and altering in direction 
so little and so slowly as to have no effect on the accuracy of the measure- 
ments. These occur over only about 5 mm. at the tip of the root and result 
in a sharp inward bend of the tip, which makes measurement impossible. 
More than one in two of the roots used curved in this way so that they 
could not be measured at all, and of the others, most could be measured 
only for two half-hours. Any number of measurements, however great at 
