52 
Journal of Agricultural Research 
Vol. XXIV, No. I 
MOVKMKNT OF PLANT FOODS IN THE SOIL 
Ions are mobile and bear plus or minus charges of electricity. It 
has long been the opinion of the writer that the demand for food origi¬ 
nates in the tissues of the plant and is carried to the absorbing surface 
of the root by means of an unsaturated carbon compound bearing a plus 
or minus charge. In the case of potassium, for. example, the plant 
protoplasm in a leaf cell may remove an atom of K from a colloidal 
compound and use it in building up a permanent compound, which 
is to be one of the final constituents of its tissues. The removal 
of the atom K, bearing a plus charge, from its colloidal compound 
leaves that compound or molecule out of equilibrium and with a minus 
charge. This charge is transmitted, by replacement and not by 
bodily movement, down through the cells to the root tips and there 
appears as a minus charge. If potassium chlorid appears in the nutri¬ 
ent solution ionized as a plus K and a minus Cl, the plus ion will be 
attracted to the negative charge, and a chemical combination will take 
place, with the formation of a molecule in equilibrium, with respect to 
plus and minus electrictity. The potassium could, in this way, be 
transported from the absorbing surface of the root to the extreme tips 
of the plant without a bodily movement through the sap. In the case 
of nitrates the opposite conditions might prevail. A demand for NO3 
might originate in the tissues and be carried to the root as an unsaturated 
compound bearing a plus charge. This would be neutralized, for ex¬ 
ample, by the NO3 ion of NaNOg. 
It is possible that the absorbing surface of the root or its walls are 
actually impermeable to the salts needed in nutrition, and it is possible 
to assume ^at food material may be transported from the roots to the 
rest of the plant without materially affecting the osmotic pressure of the 
sap. If the food materials are flowing freely in the sap and were it 
necessary for the plant to remove these materials in the localities where 
they were needed, it seems probable that there might be times when a 
high demand and a low supply, or the reverse, might cause considerable 
fluctuation in the concentration of the sap. As the writer understands 
it, the sap of plants of like varieties grown in the same localities is fairly 
constant. The tendency of the plant seems to be to keep its solutions 
in equilibrium, and the writer can conceive of a plant acting much like 
the battery of an automobile—the needle of the indicator may register 
a charge at one instant and a discharge at the next. The plant probably 
vibrates around the equilibrium point as closely as possible, taking up a 
plus charge at one time and a minus charge at another. The ordinary 
plant uses more of the mineral bases than it does of the mineral acids, 
and the writer is fairly well convinced that in order to maintain equilib¬ 
rium the plant can absorb otherwise useless acids or bases, use them as 
ions when necessary, and eliminate them in various ways. With cer¬ 
tain plants, if the system is basic, they seem to absorb CO3 as an acid 
radical for the purpose of maintaining equilibrium; and in case the 
system becomes too acid they seem to possess the power of exuding 
the carbonates as COg. The absorption of calcium by certain plants 
and its elimination as an oxalate might be explained in this way. The 
absorption of silica in large quantities may probably be traced to the 
presence of an excess of basic radicals in those plants. The plants that 
have this characteristic have usually had waterlogged marsh lands for 
their habitat, and in the ages of their adaptation have had a large 
quantity of soluble silica and a small quantity of carbon dioxid at their 
