26 
Leitch . — Some Experiments on the Influence of 
Askenasy (’ 90 ) finds for Zea Mats that the Grand Period curve is very 
flat ; the maximum rate of growth is reached when the roots are 30 to 
40 mm. long, and the rate remains constant till the appearance of the side- 
roots when the main roots are about 130 mm. long. He finds also, that in 
roots grown at a high temperature and suddenly subjected to a temperature 
of 3 0 to 6° the growth is suddenly stopped (contraction usually occurs), and 
that, on the return of the roots to the initial temperature, the rate is 
depressed below the normal rate, for a time depending on the lowness 
of the intermediate temperature, and the length of their subjection to it. 
True (’ 95 ) confirms these latter experiments of Askenasy, using 
Vida Fab a, Lupinus albas, and Pisum sativum , and finds further that 
a sudden change from a low to a high temperature is, if the interval 
be great enough (from 3 0 to 18 0 ), followed by a sudden elongation of 
the root, with a subsequent period of depressed growth. His experiments 
with Vicia Faba on the effect of transitions between 18 0 and 30° are of very 
doubtful value, since 30° is, for Vicia , 4 above the optimum \ 
More recently Schmidt (T 3 ) has demonstrated for Humulus Lupulus the 
very close dependence of growth, under ordinary open-air conditions, upon 
temperature. His growth and temperature curves vary, in all cases, in the 
same manner, and often (cf. No. 17) almost exactly proportionally. 
Finally, Vogt (cited in Jost, T 3 ) gives a series of determinations, 
but here nothing is told of the method of experimentation, and the 
experimentation-time is again 24 hours, a time, as will appear later, 
much too long, at least for high temperatures. 
The experiments to be described are on Pisum sativum , the material 
belonging to one sample, carefully mixed at the beginning ; and they are in 
two parts. The first part consists of experiments with the long experimenta- 
tion-time of 22J hours. Their purpose was, first, to map out the field, and 
second, by the use of much larger numbers than is possible in more accurate 
microscopic work, to afford an idea of the amount of variation in the 
material. In the second part, the experimentation-time is short, and the 
determinations made by microscope measurements. 
First Series. 
The time occupied daily in preparing material and making measure- 
ments in the first series of experiments being about one and a half hours, 
the experimentation-time became conveniently 22^- hours. At first (the 
experiments were begun in December), the peas were soaked and germi- 
nated at room temperature, about 15 0 C. during the day. But soon it was 
found that the temperature fell too low during the night to give a suitable 
length of root on the third day, and from then onwards the soaking and 
germination took place in an electric thermostat whose temperature varied 
slowly between 15 0 and 17 0 C. The peas germinated in an apparatus first 
