54 
Journal of Agricultural Research 
Vol. XXIV, No. I 
CONCLUSIONS 
(1) A demand for plant food may be developed in the tissues of plants, 
and this demand may be measured by analytical methods. 
(2) The demand of the plant seems to be for particular foods, and the 
effect of an application of plant food as a fertilizer seems to be largely 
a direct action upon the plant itself and not an indirect action upon 
some constituent of the soil. 
(3) Plants probably feed upon ions, and these ions probably penetrate 
the root membrane and move through the colloids to the tissues as an 
electrical charge; therefore the feeding of plants may be looked upon as 
an electrical phenomenon. 
(4) Ions are mobile and may move through the soil solution freely 
as such; and, this being the case, the plant may not be dependent upon 
the soil grains that touch its roots for nutrient material but may feed 
at a distance from the source of supply. 
