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344
cannot be evaded. The general method of experimental plant-
physiology, to vary one single factor, keeping all others constant
‘cannot be employed here, since the actual amount of two salts
has to be varied, as soon as the ratio between two ions is changed,
the total concentration of the solution being kept constant. In
highly concentrated solutions, however, the resulting growth can be
considered as due to the antagonism alone, because of the very
slight influence of the nutritive function of the different ions in
concentrations where at any rate the food is more than sufficient,
while in very dilute solutions this effect of the salts is too great
to be disregarded. Osrernour states (1907, p. 318 [13]): “In extre-
mely weak solutions all these toxic effects disappear and then only
the nutritive function of calcium is exercised” and (1916, p. 541
[18]: “Below the saturation point", (is taken to mean the point
at which the plasmatie surface is saturated with the antagonizing
salts) “the relative proportions of the salts will be of less import-
ance than their total concentration, this is the case of low con-
centrations in the region of the so called ‘nutritive effects." The
fact that in his experiments the antagonism curves flatten out for
a gradually decreasing concentration, (1914, p. 368 [17]), does not
necessarily, according to the opinion of the author, lead to the
conelusion that the importance of the ratio can be disregarded in
comparison with the nutritive effect in these low concentrations,
even if these curves cannot be due to the antagonistic effect alone.
Because this does not exclude the possibility of a simultaneous
exercise of the nutritive and antagonistic func-
tions of the salts, both being of importance for
the production curve. Osrernovr (1914, p. 369 [17]
chooses his concentrations of the pure salts in such a way that
the growth in them shall be equal. The dilute solutions of the
pure salts are not therefore necessarily of the same nutritive or
protective value (“equally toxic", 1. c.), because if it is true that
both nutritive and antagonistic functions are exercised, the equality
in growth in the two solutions only shows that the results of these
two effects combined are the same although each of them may be
different in the two cases. The straight line to which the curves
tend with decreasing concentration, may be explained with OSTER-
nour by the assumption, that the antagonistic effect (the term li-
mited as above) is of little importance in comparison with the
nutritive effect, or it may equally well be explained on the as-
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