Apr. 16,1917 
A bsorption of Nutrients 
9i 
maximum absorption by means of only a portion of its roots. It is not 
felt that a fully adequate explanation can be given of these facts until 
more is known of the mechanism and dynamics of absorption, translo¬ 
cation, and utilization of mineral elements in the plant. The following 
explanation is offered, not as an hypothesis, but more as a suggestion of 
the general way in which the results may have been brought about. 
Roughly it may be said that the absorption of a mineral element is de¬ 
pendent on utilization, that, as the ions are removed by formation of new 
compounds, etc., in the plant, more ions can be absorbed. Under the 
special conditions of the tests described here, absorption is primarily 
dependent on utilization, but the rate at which ions can be translocated 
from the absorbing cells to the utilizing cells also affects both utilization 
and absorption. 1 When one-half the roots of a plant are supplied with 
an ion, it may be said that the plant absorbs only three-fourths as much 
of the ion as when all the roots are supplied, because the rate of trans¬ 
ference from the absorbing cells to the utilizing cells is diminished by 
one-fourth. The transference of ions from the cells where they are 
absorbed to the cells where they are utilized, of course, involves a series 
of translocations. In speaking, as is done above, of the rate of trans¬ 
ference from absorbing to utilizing cell, the average.rate of the whole 
series of translocations is understood. 
While the total amount of an ion absorbed by a plant would thus be 
partially dependent on the rate at which the whole series of transferences 
from absorbing to utilizing cells proceeded, the quantity of an ion 
absorbed per gram of roots would depend, not on the rate of the whole 
series of translocations, but on the rate of translocation from the root 
cells. It can be supposed that the fewer the roots supplied With an ion, 
the faster will the translocation of the ion from the absorbing and root 
cells proceed, but the slower will be the rate of the whole series of trans¬ 
locations. Thus, when a portion of the roots are supplied with an ion, 
the amount absorbed per gram of roots may be greater and the total 
absorbed may be less than when all the roots of a plant are supplied with 
an ion. This is illustrated in figure 2. 
In this figure DE represents the rate of transference in the plant 
when one-fourth the roots are supplied with an ion, and AB the rate 
when all the roots are supplied. The rate of transference at 0 , the 
absorbing cells, are respectively DO and AO , DO being 2.26 times AO. 
The average rates of the whole curves are an< ^ the former 
being 0.55 of the latter. 
As the conditions of the preceding experiments were ideal in the sense 
that there were sufficient available mineral nutrients at all times, the 
results were due to the way the plant functions in absorbing mineral 
elements. The results are, therefore, to a certain extent applicable to 
soil conditions and have a direct practical bearing. 
1 Utilization and absorption are, of course, reciprocally dependent. 
