V. 
The Influence of Light upon tlie Growth of Leaves. 
By 
Sydney H. Vines, 
B. A., Cantab. 
The observations of Sachs 1 ) upon ihe growth of internodes have shewn 
that it presents a certain daily periodicity, which he ascribes to the aller- 
nalion of day and night. An examination of the curves which he gives 
shews that the maximum of growth usually occurs belween six and nine 
in the morning, the minimum belween three and six in the afternoon. 
x 
lf a correction for temperature be made by means of Sachs’ formula ^_ n 
(where x is the amount of increase in length during any given time, 
t the temperature, and n a number which increases from nothing to a 
little less than the smailest t ), the occurrence of the maxima of the various 
curves in the morning and of the minima in the afternoon is rendered 
1) Arb. des bot. Inst, in Würzburg. Heft II. 1873. 
2 Note on Sachs' formula. As the true significance of this formula is 
frequenlly misunderstood (see, for instanee, Stehler in Jahrb. für wiss. Bot. Bd. XI. 
Heft 1. 1877), it may be well to append a short explanation. 
The object of it is merely to eliminate all variations of growth which are pro- 
duced 1>\ variations in temperature, and by this means to obtain a curve which re- 
prcsenls more accurately the effect produced by the action of light upon growth. 
Assuming that the increase in rapidity of growth is proportional to the rise ol 
temperature, the expression would represent the amount of increase in rapidity 
for eacli degree of temperature (where x is the amount of increase in length in a 
unit of time° and l the temperature). This, however, would be incorrect, for growth 
does not commence at 0<>C., but at a temperature of several degrees. In order 
therefore to ascerlain the true value of the increased rapidity of growth due to each 
degree of temperature, the temperature must be calculated form that at which Ihe 
growth of the plant begins. Taking m to represent this minimum temperature, the 
expression -2- becomes The minimum temperature at which growth can 
tako place in any particular plant, has not always been determined cxperimentally. 
A minimum temperature must therefore be assumed, and that one is selected which 
most eflectually removes from the curve of growth the inequalilies due to variations 
of temperature. 
An example may perhaps serve to make this explanation clearer. 
An internode grows 4 mm in an hour, in the dark Ihe temperature being 20» C. 
