246 Priestley and Pearsall. — Growth Studies . II. 
1 • 
activity of the growing-point ; (2) the hydrolysis and delivery of growth- 
promoting substances from the seed reserves. An increase of temperature 
probably affects the chemical reactions of the growing-point and the 
hydrolytic reactions in the cotyledons to a similar extent. There would 
thus be an increased growth-rate and increased rate of formation of food 
material, but the latter is not formed at the root tip and some time must 
elapse before it can diffuse to the growing-point from the cotyledons. We 
should expect to observe, therefore, an initial increase in the meristematic 
activity of the root tip, due to the temperature effect on the chemical 
reactions involved. But, as in the work of Blackman and Matthaei ( 1 , 2), it 
may be assumed that the increase in rate differs in the different processes in 
Fig. 4. The growth of pea roots at high temperature (35 0 C.). (After Leitch.) 
the growth series, resulting in dislocation of metabolism. The initial increase 
in growth-rate will be rapidly followed, therefore, by a decrease. An hour or 
two after the start of the experiment an increased supply of food material 
becomes available, from the increased rate of hydrolysis in the cotyledons. 
A secondary temporary increase in growth-rate then appears, until the 
whole process is slowed down by increasing dislocation of metabolism. 
The secondary maximum in growth-rate obtained by Miss Leitch thus 
falls in line with the point of view advanced here. This secondary maximum 
may be expected to show a relation to the length of the root at the time 
measurements are made, and it would seem possible to obtain interesting data 
as to the rate at which materials move in translocation by a development 
of this method. 
