3o8 
Journal of Agricultural Research 
Vol. XXVI, No, 7 
data upon these plants are lacking. Almost without exception the 
alkalinity or basic character of a soil is due to carbonate of lime, which 
is the form of lime that a great class of plants “love.” Eliminating the 
so-called “antagonistic” effect of calcium, it is significant that these 
plants “love” other forms of lime, such as calcium chlorid or calcium 
nitrate, little more than they “love” the same compounds of potassium 
or sodium. The limit of endurance of plants for die common calcium 
salts, the sulphate, chlorid, nitrate and carbonate, is usually higher than 
for the corresponding sodium salts, because the plant, in its adaptation, 
is more accustomed to the salts of calcium than to those of sodium. 
As far as the beneficial effect is concerned, there is little difference 
between calcium chlorid and sodium chlorid, or between calcium nitrate 
and sodium nitrate. When a compound of lime, such as calcium hy- 
droxid, which the plant has never encountered in its age of adaptation, 
is placed in a culture medium, it is even more toxic than the same com¬ 
pound of sodium. For instance, calcium hydroxid is much more toxic 
to the plants that the writer has worked with than are sodium hydroxid 
or potassium hydroxid. 
It is calcium carbonate that determines whether or not a plant is 
“lime-loving// and one can often produce the same type of beneficial 
results with potassium carbonate. It is not unreasonable to question 
the application of the term “lime-loving” as applied to plants. The 
term might more properly be “carbonate-loving.” 
Assuming that there is a demand for C 0 3 within the tissues of a plant, 
that in response to the demand this radical is absorbed by the roots, and 
that the carbon thus obtained is not used to any great extent in building 
up carbohydrates or other carbon compounds, a different hypothesis is 
needed to explain the fondness of the plant for carbonates. 
Some work has been done upon the relation of the reaction of the 
plant sap to the action of the culture solution. Hoagland 2 has shown 
that the plant tends to adjust the action of a nutrient solution in the 
direction of the reaction of its own sap by absorbing the acid or basic 
radicals in the proportion needed to accomplish its purpose. Since the 
completion of the work here reported, Truog 3 has produced evidence 
tending to show that carbonates or bicarbonates may be used in the 
regulation of the action of plant proteins and the plant sap in precipi¬ 
tating oxalic and other acids out of solution in the sap. The writer's 
experiments indicate that the plant probably absorbs the C 0 3 ion or 
exudes C 0 2 in order to maintain equilibrium in its tissues. 
Referring again to Tables I and II, it will be seen that the absorption 
of a base, like potassium, seems dependent to a large extent upon the 
absorption of an equivalent amount of an acid radical or upon the 
neutralizing action of some other salt in the nutrient solution. The 
selective absorption that is so highly developed in plants is marked in 
the absorption of potassium. A rapid absorption of potassium from a 
nutrient solution would not only leave the solution acid, but would tend 
to make the plant sap basic. If the plants feed upon ions bearing electric 
charges, and if these charges are not discharged when the ions enter the 
system, it is not supposable that either the nutrient solution or the plant 
sap will remain long out of equilibrium with respect to positive or nega- 
* HOAGLAND, D. R. THE RELATION OF THE PLANT TO THE REACTION OF THE NUTRIENT SOLUTION. In 
Science, n. s., v. 48, p. 422-425. 1918. Bibliographical footnotes. 
* Troug, K. the feeding power of plants. In Science, n. s., v. 56, p. 294-298. 1922. Biblio¬ 
graphical footnotes. 
