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857
varialion in the amount of chlorine, finally, the only other possible
influence upon the curves that has not been discussed above,
being in the first experiment 0.0910—0.0826 gr./l. sol., in the second
0.0910—0.0261 gr./l. sol., may be of a certain influence. The question
of the effect of chlorine is on the whole obscure (see CZAPEK 1920
[6] IL p. 518—519). The effect of chlorine is very probably not
large enough to explain the great differences in point VI of the
curves,
In summarizing the complete discussion above the author holds
that the difference between the curves can only
be explained on the assumption that antagonism
between calcium and sodium is of influence on
the growth in the first experiment together with
other effects of the salts, and that this is probably
the most important cause of the difference in the
optimal point VI.
An objection which might be raised against comparison be-
tween the two curves will be discussed here in a few words. One
might perhaps say that the two experiments were not comparable,
having been carried out in different summers, the first out of doors,
the second in a green-house, the first with several plants in large
culture jars, the second with one plant in small culture bottles.
Taking into consideration the opinion of Mrrscneruicn (1921, [12]
p. 75) that the production factors work independently, these dif-
ferences should not affect a comparison between the relative values
of the dry-weights. Several objections to MITSCHERLICH’s theory
have, however, been raised (compare for example RIPPEL 1922,
[23] p. 24—26) and it might very well be possible that MirscHer-
LIcH’S theory cannot be applied in our case. (Compare, however,
RIPPEL, |. c. p. 33.) If this is so, the author points out that the
new striking results are obtained in the first experiment, with a
safe indication of two optima in the production curve. The se-
cond experiment, however, gave a curye, agreeing comparatively
well with the usual logarithmical form!, often under greatly vary-
’ The most important deviation from the logarithmical form is due to a re-
latively high value in point I. In examining the dry-weights of the separate
plants of this culture, one extremely high value was noted, being 125% of the
average of the rest. If this plant were to be excluded, which was not done in
calculating the curve of figure 6, the resultant curve should show a very satis-
factory agreement with the curve of closest fit according to BaurE (1918, [4] p. 375).
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