The most important work on the microscopic structure of the tissues of sumach and its adulterants was done by Andreasch, when during the later stages of his last illness he was obliged to winter in Sicily.[142] His work will well repay study, but unfortunately does not admit of useful abstraction here. A very useful investigation was also made in the Author’s laboratory by Messrs. M. C. Lamb and W. H. Harrison,[143] as regards the treatment and examination of the leaf-cuticles, which renders the detection of mixture comparatively easy. For details, the original memoir must be consulted, but if the suspected sumach be gently warmed for a few minutes with strong nitric acid, its more delicate leaf structure is entirely destroyed, and after washing and neutralising with sodium carbonate the strong cuticles of the leaves of the more common adulterants, “schinia” (_Pistacia lentiscus_), “stinco” (_Coriaria myrtifolia_), “brusca” (_Tamarix africana_), and _Ailantus glandulosa_ are uninjured, and easily recognised. Examination is rendered easier by dyeing the cuticles; safranine, acid green, Bismarck brown, and naphthol yellow being suitable for the purpose. Mr. Lamb’s photographs of the cuticles are reproduced on Plates III. and IV., but if possible, it is most satisfactory to compare the suspected sample direct with known specimens of the adulterants. [142] ‘Sicilianischer Sumach und seine Verfalschung,’ Wien, 1898. [143] ‘Sumach and the Microscopic Detection of its Adulterants,’ Journ. Soc. Dyers and Colorists, March 1899. [Illustration: FIG. 54.--American Sumach (_Rhus glabra_).] _R. glabra_, Southern States, U.S.A. (Fig. 54). Very largely used in the States to take the place of Sicilian sumach. A sample collected by the late Professor Trimble, and analysed in the Leather Industries Laboratory, contained 25 per cent. of tannin and produced a leather of very much darker colour than Sicilian. _R. typhina_, “staghorn” or Virginian sumach, contains 10-18 per cent. of tannin. A sample from same source as above contained 13 per cent. _R. cotonoides_, U.S.A. The analysis of a sample of this material gave 21 per cent. of tanning matter, and leather tanned with it was almost equal in colour to that from _R. glabra_. Other sorts found in States: _R. semialata_ (5 per cent. tannin); _R. aromatica_ (13 per cent. tannin); _R. metopium_ (8 per cent.); _R. copallina_, _R. pumila_, _R. canadensis_; _R. toxicodendron_ is the well-known “poison ivy,” a climbing plant which causes a severe and irritating eruption if touched. _R. glabra_ and _R. copallina_ are chiefly recommended for extended cultivation in the United States.