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346
chosen, which has the comparatively low Pır-optimum of about
5 and is not very much sensitive to changes in Pu, though more
sensitive than other breeds of oats to changes in the ratio be-
tween metal ions. (These particulars of the behaviour of Dala-oats
were kindly communicated by Arruenius.) The original Py-value
was adjusted to 4.5—4.9 (determined after Clark’s method, the
experimental error being included between the limits) and a control
from each pot showed after six weeks in culture the same limits
for the Py-value. This does not necessarily indicate that Py was
constant during the whole time. The variation curve for Pi is,
however, in continuously renewed solution, more simple than the
same curve for usual water-cultures, according to ALLISON and Snive
(1923, p. 564 [1]). The amount of calcium was also determined
after six weeks, in each ratio, the concentration being constant
between the limits + 2% of each concentration,
The first experiment was carried out in Sweden in 1922 in the open
air, with 6 lit. earthen-ware jars with perforated, paralfined paper-
plates, in each of which about 20 plants were planted in cotton-wool.
The solutions were almost daily directly aerated and all tubes and
jars well purified. For the solutions physiologically pure distilled
water and Kahlbaum’s pure salts were used. The solutions con-
tained 0.1gr./l. sol. (KH, PO, + K,H PO,) (the proportions of the
phosphates were such that the Py of the whole solution became
equal to 4.5—4.9), further 0.14gr./l. sol. MgSO,. 7 H,O, 0.3gr./1. sol.
KNO, and 0.04gr./1. sol. FeCl. CaCl,. 6 H,O and NaCl were added
in seven different proportions, viz.:
Weight Ca _ , 100 4, 90 (4 80 pv. 50 v. 20 uu, 0
Weight Na O05 Eile 20° ^50 780° 90° 1007
the weight of Ca-ions (= 0.0365 gr.) in one litre of the solution,
0.2008r./l. sol. CaCl,. 6 H,O, putas 100. Thus the proportions were
taken in weight of the ions, the sum of the weights of Na and Ca
being constant throughout the experiment. As we do not know,
whether the influence of the ions is due to their number or their
weight, and as besides the production was measured by weight of
the dry-substance, in which the weight of the absorbed ions is
included, the author considers it in principle more correct to base
the calculation of the solutions on the weight of the ions. The
unavoidable difference in the osmotic pressure is only + 6% of
the average total osmotic pressure of the solutions, and we
may assume — in the absence of safe experimental data — that
50 20) 10
r, I r VI
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