## 2 Results and Discussion  
### In Vitro Cultures  
The conducted analysis of variance showed that the type of starting material was significant for most of the analyzed characteristics, except for the length of the largest lateral new shoots and the number of new lateral shoots. The mean values were grouped using [PERSON]'s test (Table 1). A significant influence of the medium was noted for features such as plant height, the length of the smallest lateral branches, and root length (Figure 1). Interactions between the medium and the type of explants were significant for four parameters, namely plant height, length of smallest new side shoots, number of new modal segments, and average root length (Table 1). No source of variance related to the medium, type of explant, or the interaction between them was statistically significant for the average number of new shoots and the length of the largest lateral new shoots. [PERSON]'s test showed that the highest average plant height was obtained for plants cultivated on control media MS-K and MS-3 when the source of explants was apical meristems, while the remaining values obtained for explants were almost 50% lower. Generally, after four weeks of cultivation, taller plants for both types of explant used for study were observed on MS-K medium without PGR and with the addition of auxin-IBA at a concentration 0.5 mg: \(\upmu\)m\({}^{-3}\) (Figure 1), which was justified in the absence of cytokinins in the medium. Cytokines generally inhibit the elongation of cells but promote their division in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance and axillary bud growth. In turn, auxins usually affect elongation growth and rooting and inhibit the development of lateral shoots. The balance between auxins and cytokins plays a key role in favorable plant growth in tissue culture conditions. In the case of nodal explants as the source for our experiment, differences between particular averages were similar (Table 1). In summary, for two types of explant source-apical meristem and nodal segments-the number of new nodal segments depended on the presence of PGRs in the medium (Figure 1), with the best results observed for the MS-3 medium  
In this case, similar results were observed for both types of explant. Higher values were obtained for lateral meristems, where the largest average minimum length of lateral shoots reached over 4.5 cm (MS-3) in the presence of auxin. Explants developed from apical meristems cultivated on the control medium were almost twice as low as those from lateral meristems. Excluding control media, the lowest values were observed for the MS-4 medium, which was supplemented only by cytokin at 0.5 mg-dm\({}^{-3}\) BA, regardless of the type of explant (Table 1). The importance of choosing the right type of explant has been mentioned several times in research into mint. The experiment of [PERSON] et al. (2016) [PERSON] et al. (2016) aimed to study the concentration of IBA for root regeneration, depending on the explant used. The nodal segment shoot tips and leaves were assessed at three IBA levels (1.0, 2.0, and 3.0 mg-dm\({}^{-3}\)) together with root regeneration control. The results revealed that the apical and lateral meristem performed better than the leaves in all combinations tested. It was shown that for in vitro regeneration of mint roots, the best results were obtained with 1.0 mg-dm\({}^{-3}\) IBA with explants from apical or nodal segments. [PERSON] and [PERSON] (2018) [PERSON] and [PERSON] (2018) conducted a similar experiment for the selected mint genotype (_Mentha_ sp. ), in which the same BAP concentrations and types of explants were used. The results showed much better shoot proliferation rates for apical and lateral meristems. Additionally, good results were obtained in our study for explants from an apical and lateral meristem. The same types of explant were also used in the experiment of [PERSON] et al. (2017) [PERSON] et al.