In Polish plants of Aldrovanda vesiculosa growing in a half-strength B5 medium with different KNO
3 concentrations, the medium with 1000mgl
-1 KNO
3 was the best in all characteristics. The addition of 100, 300 and 1000mgl
-1 peptone to half-strength B5 medium with 500mgl
-1 KNO
3 for Polish plants led to a step-wise increase of all growth characteristics but usually only the effect of 300 and 1000mgl
-1 peptone was statistically significant. No clear relationship was found between growth characteristics and KNO
3 concentration in a half-strength B5 for Japanese plants. The addition of 100, 300 and 1000mgl
-1 peptone to a half-strength B5 medium with 500mgl
-1 KNO
3 led to a two- to threefold increase in the number of shoot apices. pH values below 3.0 in used B5 media were not toxic for the growth of Aldrovanda in vitro. In both strains of Aldrovanda tested, the full-strength B5 medium with 2500mgl
-1 KNO
3 appeared to be excessively concentrated for optimal growth.
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