Plant leaves are warmed on a water-bath with dil. HCl to decompose glycosides, dried and put to microsublimation. The sublimate is dissolved in a small amount of water and a piece of quinone crystal is added. The black quinehydrone-like substance here formed is observed under a microscope. This and the reaction using purpureo-salt instead of oxidase seem to point that a phenol-glycoside is widely distributed in various leaves, the amount of which is larger in leaves that turn black on heating. Leaves from 250 kinds of domestic plants were examined and 91 of them gave positive reactions. It was assumed that the source of blackening is phenols or o- or p-hydroxyl compounds. From the fact that the diameter of a “black-ring” that appears on a fresh leaf when pressed with heated glass rod, is always larger in the leaf in which cuticle is well-developed, it seems that the dispersion of steam extends to larger areas in such leaves. It is therefore proposed that the strength of the cuticle be indicated by the diameter of the black-ring formed under a definite condition. The leaves that form black-ring of a large diameter due to well-developed cuticle, generally contain a large amount of triterpenes.

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