Diurnal Variations in the Total Nitrogen Content 
of Foliage Leaves. 
BY 
ALBERT CHARLES CHIBNALL. 
{From the Bioche?nical Department , Imperial College of Science and Technology .) 
D URING the past two or three years the writer has had occasion to 
refer to the literature dealing with the nitrogen content of leaves. 
It is a subject that has been treated by chemist, botanist, and agriculturist, 
consequently papers concerning it are scattered in a number of journals of 
diverse interests, often difficult of access. Czapek ( 3 ) has made a praise¬ 
worthy effort to collect them, but the limitations imposed on the writer of 
a handbook such as his have naturally prevented him giving anything but 
the briefest discussion on the subject-matter contained therein. 
In the present paper the author proposes to discuss only one aspect of 
the subject, that concerning the diurnal variations in the total nitrogen con¬ 
tent of leaves. He is prompted to do this because some workers have 
failed to grasp one significant fact when estimating these variations, namely, 
that the total nitrogen makes up but a small fraction of the total weight of 
a leaf, and that the large normal variation in other constituents of the leaf, 
such as carbohydrates or water, may quite prevent the change in total nitro¬ 
gen appearing in its true value unless proper allowances are made. 
A diurnal change in the nitrogen content of a leaf at night, if it can be 
definitely established, is a point of physiological interest, in that it may be 
used as a stepping stone to the elucidation of a complex and important 
problem that is still more or less a mystery, that of the nitrogenous meta¬ 
bolism in the leaf. 
At any moment the total nitrogen content of a leaf depends on the two 
following variables: 
i. The rate of translocation through the petiole into the leaf of simple 
nitrogenous substances, such as nitrates, ammonium salts, &c., from the root 
system. 
2 . The rate of translocation of nitrogenous substances out of the leaf 
through the petiole to other parts of the plant. If (i) rises relative 
to (2) nitrogen will accumulate; whilst if (1) falls relative to (2) nitrogen 
[Annals of Botany, Vol. XXXVII. No. CXLVII. July, 1923.] 
L 1 2 
