Apart from microscopic characteristics, the external appearance of barks, both to the naked eye and by the aid of a lens, forms a valuable means of recognition. The arrangement of the bast and corky layers, the remains of epidermis, or the form and character of the fissures, and of the lenticels or small corky protuberances which take the place of stomata in the epidermis, should be observed. Space does not permit of any detailed account of the structure of fruits, wood and leaves, which are also cellular structures in many respects resembling the bark. The cuticles of leaves, and especially the stomata or breathing pores, and the hairs are often very characteristic. (Cp. Plates III. and IV., and p. 272.) Valuable hints may also be obtained from the chemical reactions which are described on p. 70 _et seq._, L.I.L.B. BOTANICAL LIST OF TANNING MATERIALS.[135] [135] The percentage of tannin given where the source of information is not stated must in many cases be regarded as uncertain, many analyses having been made before the introduction of modern methods, but those quoted as having been done in the author’s laboratory are of recent date and have been made by the latest methods. CONIFERÆ, Pines, Cypresses, mostly containing Catechol tans, yielding reds. _Abies excelsa_, Lam. (_Pinus Abies_, _Pinus Picea_, _Picea vulgaris_, Link.), Norway Spruce. Fr. _Faux sapin_; Ger. _Fichte_, _Rottanne_. The source of the so-called larch-extract, and a principal tanning material of Austria. Contains 7-13 per cent. of a catechol-tannin and much fermentable sugar, and on this account is useful for swelling and colouring, but does not tan heavily. English and Scandinavian bark does not seem much utilised. Best bark 2-8 mm. thick; smooth, yellow inside, with reddish-brown ross outside. For detailed description of structure see von Höhnel, ‘Die Gerberinden,’ p. 35. _Abies pectinata_, Silver Fir. Fr. _Sapin_; Ger. _Edeltanne_, _Silbertanne_, _Weisstanne_. Used to a limited extent, but apt to be confused with spruce. Contains 6-15 per cent. iron-blueing tannin. Used in Styria, Austria, Russia. Without “ross,” but silver-grey and smooth outside. (Von Höhnel, ‘Die Gerberinden,’ p. 40; ‘Gerber,’ 1875, p. 375.)