Stomatal index (S.I.) was examined in the birch leaves from Betula pendula ROTH and B. pubescens EHRH. collected during vegetation in different localities. Its value lies within 3.30 ± 1.31 – 7.33 ± 3.13 in Betula pendula ROTH and 3.66 ± 1.34 – 12.06 ± 3.26 in the species Betula pubescens EHRH. With greater or lesser significance, the S.I. value is dependent on the age of the leaf, mother plant and locality.

        Key words: stomatal index – quantitative microscopy – Betulae folium