AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
a medium which can be used effectively for young wheat seedHngs for at 
least twenty-four hours and without any harmful effects. Furthermore, 
table I shows that when MgHP04 or KNO3 was one of the salts of a type 
(see types II and III), larger plants were produced than when neither of 
these salts was contained in the type. 
In recapitulating the conclusions, it seems that the availability and 
utilization of essential elements by wheat seedlings are not inconsiderably 
affected by the way in which these elements, presumably as ions, are paired. 
There undoubtedly is one kind of ion, or possibly more, of opposite charge 
with which any one of the essential ions can be used to best advantage by 
the plants. There is more than presumptive evidence in the results of this 
experiment that the proper pairing of nutrient elements, or of ions of 
opposite charge, is an important factor, and one that does account in a 
large measure for the physiological adaptability of a nutrient solution for 
plant growth. However, this pairing of any two ions in complete nutrient 
solutions does not mean that any definite cation-anion ratio must prevail. 
Investigations have shown that ionic ratios of nutrient solutions can cover 
a considerable range of values without any apparent physiological effect. 
However, the interpretation of this test should mean that if a nutrient solu- 
tion is a poor medium for plant growth because of the large proportion of 
one ion, it should be improved by the addition of some other ion of opposite 
charge, even though this be added in the form of a salt that would also add 
more of the ion already in excess. That this is what actually happens, has 
been proven experimentally in this laboratory. The above conclusions 
may also be stated in other words, and, as a concrete example, Mg(N03)2 
can be used as the source of nitrates for plants in any growth media. But 
the utilization of nitrates by the plant will be largely influenced by the 
relative supply of available potassium in the medium; that is, the utiliza- 
tion by young wheat plants of the nitrate anion is closely related to that 
of the potassium cation, and vice versa. A cation-anion relation of other 
essential ions is apparent from a study of the results, but need not be con- 
sidered in detail in this paper as the experiments will be discussed elsewhere. 
It may not, however, be amiss to state that the principle of the method here 
employed to study the physiological properties of solutions seems to give 
promise of yielding further information on the nutrition of the higher plants 
that can not be gained by the use of complete nutrient solutions because of 
their complexity. 
University of California 
