## 2 Results and Discussion
### In Vitro Cultures
  
* Values followed by the same letter within a column are not significantly different (\(p>0.05\), Tukey’s test) for interaction, type of explant used, and medium, respectively; \(2\) ns: not significant;
* \(2.2\pm 0.54\,^{\circ}\) & \(5.0\pm 0.32\,^{\circ}\) & \(1.4\pm 0.29\,^{\circ}\) & \(3.7\pm 0.68\,^{\circ}\) & \(4.8\pm 0.58\,^{\circ}\) & \(5.4\pm 0.14\,^{\circ}\) \\ MS-1 & segment & \(6.4\pm 0.10\,^{\circ}\) & \(4.7\pm 0.55\,^{\circ}\) & \(2.3\pm 1.01\,^{\circ}\) & \(3.3\pm 0.09\,^{\circ}\) & \(4.5\pm 0.38\,^{\circ}\) & \(5.2\pm 0.14\,^{\circ}\) \\ MS-2 & & \(7.7\pm 0.25\,^{\circ}\) & \(5.5\pm 0.21\,^{\circ}\) & \(2.9\pm 0.81\,^{\circ}\) & \(3.6\pm 0.10\,^{\circ}\) & \(5.2\pm 0.25\,^{\circ}\) & \(7.0\pm 0.23\,^{\circ}\) \\ MS-3 & & \(7.2\pm 0.13\,^{\circ}\) & \(6.3\pm 0.61\,^{\circ}\) & \(1.4\pm 0.30\,^the results for MS-1 and MS-4 when apical meristems were used, and also 3-5-fold less than the value for lateral meristems on MS-2 medium. Similar tendencies were also observed for explants from the apical meristem on MS-1 control medium comparing lateral meristems (Table 1). In the case of apical meristems and nodal explants used as the initial material, the highest percentage of rooting explants was recorded on the control medium (100%), while only 37% and 83% of explants produced new lateral shoots on the control medium without PGRs, respectively (Figure 2). Rooting at the same or similar level compared to the control medium was observed in the explants with regenerated nodal segments on all tested media. The rooting of explants from the apical meristem after adding PGRs was the worst compared to rooted explants obtained from the nodal segment. These differences in rooting might have been due to the higher concentration of endogenous root-promoting substances in the nodal segments. In the case of our study, the addition of IBA did not  
Figure 1: Significant effects of media on the three evaluated traits in developing mint explants. Columns followed by the same letter are not significantly different (\(p>0.05\), [PERSON]’s test) for a significant effect of the medium; bars represent standard deviations. result in the expected positive reaction in rooting, but we noticed a better elongation growth of shoots. The development of nodal segments resulted in the same level (100%) of lateral shoot development as the control (MS-K) on MS-3 medium (0.5 mg: dm\({}^{-3}\) IBA) (Figure 3). The addition of PGRs to media caused a certain percentage of explants (%) to produce new shoots on MS-3 medium. Figure 3: Comparison of the volatile organic compound chemical compositions of plants cultivated with various combinations of tested plant growth regulators: MS-1 (1), MS-2 (2), MS-3 (3), MS-4 (4), and without regulators (5) (MS-K). Figure 2: Developed roots and lateral shoots (%) of particular types of explant cultivated on four kinds of medium-MS-4, MS-3, MS-2, and MS-1-compared to control medium (without hormones). In our study, we did not identify callus formation, but the process of direct morphogenesis from lateral buds was noted. The average number of new lateral shoots was two. The length of the largest new lateral shoots was comparable to the plant height of explants derived from shoots with an apical meristem or single-nodal segments, but the smallest new lateral shoots were shorter than 1 cm. On average, we obtained five new segments per explant after four weeks of culture. The four variants of treatment with different combinations of PGRs enabled the development of an effective protocol for the rapid propagation of the tested peppermint genotype (Torseed Company, Torun, Poland) from a shoot tip with an apical meristem and single-nodal segments.