## 3 Results and Discussion
### Growth of M. sylvestris on the 3 Metal-Contaminated Areas  
In the three areas, all life stages of _M. sylvestris_ were observed from seed germination to the growth and emergence of flowers, without any visible toxicity symptoms. Our results corroborate the results of cultivation experiments in TE-contaminated sites/pots already reported in southern Europe [29; 30; 31]. Concerning the dry weight (Table 2), a statistically significant area effect was observed (\(p<0.05\)) with a better growth in Area 3. [PERSON] et al. [34] discussed that soil fertility, notably the soil's organic matter (OM) content, could increase _M. sylvestris_ biomass production. The best biomass production and yield observed in Area 3 could be due to the higher cation exchange capacity and OM content of its soil (Table 1). To our knowledge, _M. sylvestris_ is not a common crop, with only few studies and data concerning the yield of this species being reported. In Italy, [PERSON] et al. [34] reported minimum and maximum biomass yields of 0.98 and 4.73 t ha\({}^{-1}\) of DW, with most of the yields ranging between 1-3 t ha\({}^{-1}\) of DW. The yields obtained in our study, between 2.2 and 2.9 t ha\({}^{-1}\), can therefore be considered average. As the best yield was obtained in Area 3, and our results confirmed the high tolerance of _M sylvestris_ to a high TE contamination level. Moreover, in this study, flower production was essential for assessing dye production on a contaminated site. Therefore, specific data concerning flower production were gathered, and a flower percentage per plant between 8% and 10% and a flower yield of 0.145-0.241 T ha\({}^{-1}\) of DW were obtained (Table 2). To our best knowledge there are no data available in the literature to compare our results to. As _M. sylvestris_ is usually cultivated for horticultural purposes (as ornamental crop), and it requires an agricultural technical itinerary to be cultivated in a large area for phytomanagement purposes. Based on this paper's sowing design, The soil should be worked mechanically (tillage and weeding) before sowing. The distance of 0.5 m between the seedling lines and seeds seemed appropriate for this species' growth; this could be achieved by using agricultural machinery that allows sowing in a line and that respects the distance between seedling lines. However, three factors could impede the cultivation of _M. sylvestris_ on an agricultural scale: (1) seed production should be adapted to the agricultural market; (2) a mechanical harvester should be developed, which could be the most problematic point, as the machine must cut the base of the plant and harvest it with care in order to not to damage the flower part; (3) a process for the separation of the flower from the shoots should also be developed; this could be done manually directly after the harvest, but this is time-consuming (around 15 min per plant) and could limit the economic viability of the dye. An alternative to manual separation should be investigated and tested. For example, the aerial biomass could be dried in a chamber, and the separation of flowers could be performed on the dry matter with airflow or by shaking the biomass. Flowers that had fallen to the ground by gravity would just need to be picked up. This option could be \begin{table}
\begin{tabular}{c c c c} \hline  & **Area 1** & **Area 2** & **Area 3** \\ \hline Mean dry weight (g plant\({}^{-1}\)) & 81.8 (\(\pm\)23.9) a  & 89.8 (\(\pm\)23.2) a  & 126.5 (\(\pm\)28.5) b  \\ Yield (Kg 25 m\({}^{-2}\) FW) & 31.6 & 26.3 & 38.9 \\ Yield extrapolated (ton ha\({}^{-1}\) FW) & 12.6 & 10.5 & 15.5 \\ Yield extrapolated (ton ha\({}^{-1}\) DW) & 2.3 & 2.2 & 2.9 \\ Mean flower \% by plant (FW) & 10.3 (\(\pm\)2.6) & 8.4 (\(\pm\)1.9) & 8.4 (\(\pm\)1.6) \\ Flower Yield extrapolated (ton ha\({}^{-1}\) FW) & 1.3 & 0.9 & 1.3 \\ Flower Yield extrapolated (ton ha\({}^{-1}\) DW) & 0.241 & 0.145 & 0.226 \\ \hline \end{tabular}
\end{table} 
Table 2: Yield, percentage of flowers, and plant dry weight in the three areas.