## 3 Results and Discussion
### Effect of EM and OMW Treatments on Plants Growth
LWR describes the efficiency of assimilation in the whole plant. LWR index ranged from 0.59 in O2 to 0.47 g g\({}^{-1}\) in the Control and did not show differences between treated plants, which however showed values higher than the Control (Table A4; Figure 4D). LAR defines the leaf area produced per unit of biomass and therefore it is closely related to photosynthetic activity. In the present study LAR index values in treated plants were higher compared with the Control, and the highest data was recorded in E1 (414.9 cm\({}^{2}\) g\({}^{-1}\)) followed by O2 treatment with 353.1 cm\({}^{2}\) g\({}^{-1}\) (Table A4; Figure 4E). Comparing the Control with the treatments the pairwise analysis (Table A3) showed that the maximum value of EF for SLA was \(-\)1.31 (Control\(\Leftrightarrow\)E1) and the minimum was 0.03 for Control\(\Leftrightarrow\)O1. Among the treatments, the maximum value was observed for E1\(\Leftrightarrow\)E2 (EF = 2.11) and the minimum was EF = \(-\)0.05 for E2\(\Leftrightarrow\)O1 (Table A3). Instead for LWR, the comparison between Control and treatment exhibited the maximum value in Control\(\Leftrightarrow\)O2 (EF = \(-\)3.54) and the minimum difference in Control\(\Leftrightarrow\)O1 (EF = \(-\)2.20) (Table A3). LAR showed among Control and treatment the maximum value of EF = \(-\)2.62 in Control\(\Leftrightarrow\)E1 and the minimum in Control\(\Leftrightarrow\)O1 (EF = \(-\)0.74). The highest value among treated plants was EF = 2.37 in E1\(\Leftrightarrow\)E2, and the lowest was in E2 \(\Leftrightarrow\)O1 with EF = 0.27 (Table A3). In our experimental conditions, EM and OMW determined an increase in leaf number and leaf area but did not affect leaf thickness. These results agree with [PERSON] et al. [42] that used organic fertilizers in _Menthu piperta_ L. and with [PERSON] and [PERSON] [43] for the use of biostimulants in _Solanum tuberosum_ L. The rise of LWR and LAR, due to the application of biostimulants, in combination with enlarged leaf size, can maximize the optical light interception efficiency and the greater acquisition of resources resulting in an increment of plant growth [44; 45; 46]. The presence of trichomes on the leaf surface of _Tanacetum balsamita_ was observed, and thus effect of biostimulants on the number of trichomes was evaluated. Although trichomes have been described in some species of the genus _Tanacetum_, this is the first time they are described in _Tanacetum balsamita_. Costmary presented non-glandular and glandular trichomes on the adaxial and abaxial epidermis (Figure 5A-F), even if they are both more abundant on the lower epidermis. Non-glandular trichomes are long, uniseriate T-shaped hair and consist of 2-3-foot cells and 2 acicular armed hair (Figure 5A,B,G). Glandular trichomes consist of biseriate secretory cells and a large subcuticular cavity where secretory products are stored, like the Peltate trichomes of the _Lamiaceae_ ([47; 48] (Figure 5C-E,G). Histochemical staining (Nadi Reagent) and fluorescence analysis highlighted the presence of terpen and wall-bound hydroxycinnamates in glandular trichomes (Figure 5D,E) [49; 50]. Under our experimental conditions, no statistically significant difference among treatments was found in the density of glandular trichomes while in non-glandular trichomes, the number was significantly higher in the E2 (81.3) and O1 (78.7) treatments compared to the Control (64.7) (Figure 5F-L). These results agree with the study of [PERSON] [51] who reported an increase in non-glandular hairs in potato plants after treatments with commercial organic biostimulant (Vitazyme(tm)) speculating a positive relationship among the action of biostimulant, the resistance to pathogens and trichomes number. Until now, there is no published research on the use of EM and OMW in costmany. Many studies reported a positive effect of EM on a wide range of fruits and leafy vegetables in pot and in field experiments [52], such as apples [53], beans [54] and tomato [55].