31. The specific epithet " " is from the Latin meaning " wedge-shaped ", referring to the leaf base . 32. The mine initially has the form of a short corridor that starts at the midrib or the leaf base . 33. The species name " decurrens " " decurrent " is derived from the leaf base running down the stem. 34. The specific epithet " attenuata " is from the Latin meaning " drawn out ", referring to the leaf base . 35. The mine has the form a long and narrow corridor that starts at the midrib or at the leaf base . 36. The mine has the form of one or some rather broad corridors radiating from the leaf base or the midrib. 37. They form a strongly contracted upper-surface tentiform mine, generally in the lower third of the leaf, beginning at the leaf base . 38. The leaf cells are elongated at the leaf base and smooth, the top sheet portion extends to approximately square and smooth. 39. Nor does the G . Tahan specimen have truly petiolate leaves-its leaf base is narrow and has rolled up during drying. 40. The leaf base of silver birch is usually a right angle to the stalk while for downy birch it is rounded.
