Total Nitrogen Content of Foliage Leaves. 515 
vation, that extreme flaccidity results in a decrease of approximately only 
1 per cent, of the water-content of a leaf, shows that the diurnal variation 
must be extremely small. Now water makes up 80 per cent, to 90 per cent, 
of the total weight of most fresh leaves. It would appear then that thp 
diurnal change in the total nitrogen, expressed by Method C, will approxi¬ 
mate very closely to the actual diurnal change in the leaf. It has already 
been pointed out that Method A expresses this also, but that the sampling 
errors, as shown in Table II, are greater. Method C, then, seems the best to 
adopt as a working basis. 
It is now proposed to examine some of the published results in detail. 
Schulze and Schiitz (11) These workers have made a very thorough 
investigation into the seasonal and diurnal changes in the leaves of Acer 
negundo. The leaves were picked from two trees fifteen to twenty years old, 
and those in each sample were chosen as far as possible of equal weight and 
size. The evening leaves were picked between 6 p.m. and 6.30 p.m., those 
on the following morning (except in case of 3-6 September) between 5 a.m. 
and 6.30 a.m. depending on the season. Their results, in so far as they con¬ 
cern the diurnal change in the total nitrogen, are given in Table III. The 
authors themselves used Methods A and B ; it is possible from the data 
they give to calculate C. 
Table III. 
Shozving the Fall in the Nitrogen Co 7 itent of the Leaves of Acer negundo 
at Night , expressed as a Percentage of Day Value. 
(Schulze and Schiitz) 
Date of Picking. 
Method A. 
Method B. 
MetJiod C. 
7 May 
jo-i6 
4 - 5 ° 
9.07 
6 June 
9.99 
2.08 
6-88 
5 July 
7.27 
1-76 
1-48 
2 Aug. 
3-97 
0-16 
—1-76 
3-6 Sept. 
18.50 
0.78 
11-90 
25 Sept. 
- 7-54 
1.36 
-7-18 
These figures are probably the best available at the present. In the 
absence of sampling errors those under Method A must be accepted with 
caution. Method C shows that when the leaves are young there is a large 
withdrawal at night, the amount decreasing as the leaf ages until it reaches 
a value of only 1 per cent. The apparent large gain at night observed on 
Sept. 25 may be due to dehydration, as the leaves at that date had already 
begun to fall. It will be observed from Method B that the loss of nitrogen 
at night was proportionately greater than that of other solids in the leaf. 
Suzuki ( 12 ) has examined the diurnal changes between 6 p.m. and 
6 a.m. of the plants given in Table IV, the figures in round brackets after 
each name denoting the number of leaves per sample used. 
