COMPARATIVE-STUDY OF LEAF ANATOMY AND ESSENTIAL OILS OF THE HYBRID MENTHA X VILLOSO-NERVATA AND ITS PARENTAL SPECIES MENTHA-LONGIFOLIA AND MENTHA-SPICATA

Leaves of the hybrid Mentha x villoso-nervata are covered with nonglan dular trichomes of intermediate length between those of its parental t axa M. longifolia and M. spicata. Glandular trichomes producing essent ial oils are more numerous on the lower leaf surface than on the upper one in all three mints. Their number per mm(2 )is higher in M. spicat a and it decreases in M. longifolia and M. x villoso-nervata. Stomata are also more numerous on the lower leaf surface of the three taxa, wi th M. longifolia predominating. The leaf lamina of M. x villoso-nervat a is ca. 83% thicker than that of M. longifolia and ca. 9% thicker tha n that of M. spicata. The number of chloroplasts per mm(2) of mesophyl l section (leaf cross section) is higher in M. x villoso-nervata. In l eaf paradermal sections, the sizes of the epidermal, palisade, and spo ngy parenchyma cells of M. x villoso-nervata have intermediate values between those of its parental species M. longifolia and M. spicata. M. x villoso-nervata leaves are the lowest in essential oil content. As concerns the essential oil composition, the hybrid resembles one paren t, M. longifolia, in the derivatives of piperitenone and piperitone, a nd the other parent, M. spicata, in the high amount of limonene. It di ffers, however, from its parental species in that it contains a higher amount of germacrene D.