SUM M.•\R^•The trichome number and the variability in mono and sequisterpene distribution of peltate trichome.s within a leaf was in\esliKated during development of peppermint (Mentlui X piperitti L.) leaves. A larger number of peltate trichomes was initiated on adaxial epidermises than abaxial epidermises, but during leaf development a greater yland number was produced on abaxial epidermises. I''\ idence showed that the trichome number was not fixed at the time of leaf emergence. On both epidermises, the trichome distribution was found to change with its position on the leaf. A striking monoterpene composition variability was present among indi\ idual trichomes and between different parts of the leaf. Different rates of peltate trichome development and distribution as well as significant differences in trichome number and density were found between the epidermises. . A clear and opposite trend was found between menthone and menthol percentages during development. .Menthone and menthol \\eie also found to be present in larger amounts on adaxial epidermises, whereas neomenthol and isonienthol had highest percentages on abaxial epidermises. Of the total oil collected from peltate trichomes, 60",, was composed of menthone, isomenthol, menthol and neomenthol and of the remaining 40",,, more than half was represented by (ither mono and sesc^uiterpenes while the final percentage was made up of a few unidentified earl\-eluting compounds of high volatility.

Essential oils were isolated from Artemisia abrotanum L., A. absinthium L., A. alba Turra, A. annua, L., A. campestris L. ssp. campestris, A. campestris L. ssp. borealis (Pallas) H. M. Hall et Clements, A. chamaemelifolia Vill., A. genipi Weber, A. glacialis L., A. petrosa Baumg. ssp. eriantha Ten., A. umbelliformis Lam., A. vallesiaca All., A. verlotiorum Lamotte, A. vulgaris L., growing spontaneously in the north‐west Italian Alps. GC‐MS analyses were carried out in order to determine the percentage composition of the oils. The data obtained were statistically processed in order to partition the species according to their oil composition. The results showed the presence of two main groups of plants. The first group composed of A. genipi, A. umbelliformis and A. petrosa was characterized by the presence of α‐thujone, while camphor and 1,8‐cineole characterized the oil of the remaining plants.

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A number of strains of Lactobacillus spp. from foods were screened for their ability to convert meso-2,3-butanediol into 2-butanol. Only three strains of L. brevis transformed the meso-diol into the secondary alcohol. These strains as well as the others unable to metabolize meso-2,3-butanediol exhibited the capacity to hydrogenate 2-butanone to 2-butanol. In both types of lactobacilli, an inverse relationship was observed between the diol or ketone concentration and the abundance of the R form of 2-butanol. This fact has been interpreted in terms of a co-occurrence of two dehydrogenases, both acting on the ketone with different kinetic parameters and opposite enantioselectivities. These results represent a further support to the assumption that 2-butanol present in distillates originates from the enzymatic activity of lactobacilli growing on mashes and give the most likely explanation of the enantiomeric excess of (R)-2-butanol generally found in distillates. Keywords: 2-Butanol; meso-2,3-butanediol; lactobacilli; diacetyl; acetoin; dehydrogenases

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