570 
Journal of Agricultural Research 
Vol. XXI, No. 8 
Probably the chief inhibition to translocation arises from the fact that 
nitrogen, phosphorus, and potassium are more or less scattered, as it 
were, in different parts of the plant, as a result of having been absorbed 
by different roots. Doubtless they are, for the most part, in different 
fibrovascular bundles and must be translocated by separate paths, 
instead of all together, to the cells where they are to be utilized. A 
cell, for example, which is adjacent to a fibrovascular bundle that ema¬ 
nates from a root in the phosphorus solution can secure phosphorus at 
once, but the nitrogen and potassium have to be transported from other 
centers in the plant. No more phosphorus can be assimilated by this 
cell until the nitrogen and potassium are secured. Under normal 
conditions the three elements would be obtained from the same fibro¬ 
vascular bundle and they would be assimilated more quickly. 
The foregoing suggestion concerning the manner in which translo¬ 
cation and assimilation may be depressed by a division of the roots 
between incomplete solutions seems to explain facts i and 2 of the 
summary given on page 568. The view that diminished assimilation is 
due to slow translocation rather than to a reduced power of absorption 
is also supported by the results of experiment VIII. I11 this experiment, 
where the assimilation was unusually low, the amounts of nitrogen and 
potassium in the roots were unusually large in proportion to the per¬ 
centages in the tops. 
It follows from the explanation of the way assimilation is depressed 
that when roots are in different incomplete nutrient solutions, slowness 
in the translocation or assimilation of one element reduces the rate of 
assimilation of other elements which are confined to other roots. This 
suggests a method, described below, for calculating the mean assimila¬ 
tion of those elements which are confined to certain roots, by making 
use of data presented by the authors in the previous paper. 
This earlier paper contains a graph giving a curve which shows the 
assimilation of an element (relative to the normal) that would be attained 
when any fraction of the roots were deprived of one element, the re¬ 
mainder of the roots being in a complete solution. This curve, experi¬ 
mentally determined (reproduced in the present paper in fig. 1), 
agreed very closely with Mitscherlich’s law of minimum. 
While this curve is directly valid only for the condition where part of 
the roots are in a complete solution and part in a solution lacking one 
element, nevertheless, by utilizing values obtained from it, one can 
calculate fairly closely the mean of the amounts of nitrogen, phosphorus, 
and potassium that will be assimilated when the roots are in two or three 
different solutions each of which is lacking in one or more of these ele¬ 
ments. It is only necessary to take from the curve the assimilations of 
nitrogen, phosphorous, and potassium (expressed as percentages of the 
normal assimilations) which correspond to the respective fractions of 
the roots supplied with these elements and then multiply the percentages 
