Total Nitrogen Content of Foliage Leaves. 513 
The total number of leaves from the twelve plants was 419, of total 
weight 237 grm. For a sample of this size and weight the probable errors 
in the total nitrogen are given in Table II, the nitrogen being determined 
by the Kjeldahl-Gunning method modified for the presence of nitrates. 
Table II. 
Shaving Sampling Errors in the Total Nitrogen of the Leaves of 
Vicia Faba maj. 
Weight of 
Percentage of 
Percentage of 
nitrogen 
nitrogen per 
nitrogen per 
per 100 
total dry 
total fresh 
leaves. 
leaf-weight. 
leaf-weight. 
(.Method At) 
(.Method B.) 
(.Method C.) 
Mean 
0.432 
5 - 7 r 
°*753 
Probable error 
±0-0195 
±0-036 
±0-0068 
Percentage error 
4.50 
0.63 
0.91 
The percentage error in estimating the nitrogen by Method A was 4*50, 
a figure five times as great as Method C and seven times as great as 
Method B. Undoubtedly, if circumstances are such that leaves of similar 
age and size can be used in the diurnal samples (such as the opposite 
leaflets of the pinnate leaves of the weeping ash) the probable errors by 
Method A would be lower, but in the absence of any definite data as to the 
size of these errors, Method A must be considered inferior to Methods B 
and C. 
Method B . Variation in the total dry weight of a leaf will depend on 
the assimilation of carbon dioxide from the air, on respiration, and trans¬ 
location of substances into and away from the leaf through the petiole. If 
the diurnal variation is estimated over a period of darkness, the assimilation 
of carbon dioxide will be nil. But of the substances leaving the leaf 
through the petiole only part, probably a small part, will be nitrogen. 
Clearly then, when the diurnal change in the nitrogen content of a leaf is 
being estimated by this method, it is not the absolute amounts of nitrogen 
in the leaves that are being compared, but only the concentrations of 
nitrogen in terms of total solids. For example: suppose the percentage 
loss due to translocation of total solids and total nitrogen away from leaf to 
be the same, then the percentage of nitrogen per dry weight remains 
unchanged. Similarly, if the percentage fall in the total nitrogen is greater 
than that of total solids the percentage of nitrogen per dry weight will fall, 
whilst if the percentage fall in the total nitrogen is less than that of the total 
solids, the percentage of nitrogen per dry weight will rise. Obviously this 
method is quite inapplicable for expressing the true diurnal change in the 
nitrogen content of leaves, since a loss, should it be proportionately less 
than that of the total solids, will appear as by a rise. 
It is true that Brown and Morris ( 1 ), Parkin ( 9 ), and Davis, Daish, and 
