3. _Styrolene Derivatives._--This group contains a benzene and also an ethylene group, being derived from styrolene C6H5·CH:CH2. Coniferin, C16H22O8, occurs in the cambium of coniferous woods. Emulsin converts it into glucose and coniferyl alcohol, while oxidation gives glycovanillin, which yields with emulsin glucose and vanillin (see EUGENOL and VANILLA). Syringin, which occurs in the bark of _Syringa vulgaris_, is methoxyconiferin. Phloridzin, C21H24O10, occurs in the root-bark of various fruit trees; it hydrolyses to glucose and phloretin, which is the phloroglucin ester of para-oxyhydratropic acid. It is related to the pentosides naringin, C21H26O11, which hydrolyses to rhamnose and naringenin, the phloroglucin ester of para-oxycinnamic acid, and hesperidin, C50H60O22(?), which hydrolyses to rhamnose and hesperetin, C16H14O6, the phloroglucin ester of meta-oxy-para-methoxycinnamic acid or isoferulic acid, C10H10O4. We may here include various coumarin and benzo-[gamma]-pyrone derivatives. Aesculin, C15H16O9, occurring in horse-chestnut, and daphnin, occurring in _Daphne alpina_, are isomeric; the former hydrolyses to glucose and aesculetin (4·5-dioxycoumarin), the latter to glucose and daphnetin (3·4-dioxycoumarin). Fraxin, C16H18O10, occurring in _Fraxinus excelsior_, and with aesculin in horse-chestnut, hydrolyses to glucose and fraxetin, the monomethyl ester of a trioxycoumarin. Flavone or benzo-[gamma]-pyrone derivatives are very numerous; in many cases they (or the non-sugar part of the molecule) are vegetable dyestuffs. _Quercitrin_, C21H22O12, is a yellow dyestuff found in _Quercus tinctoria_; it hydrolyses to rhamnose and quercetin, a dioxy-[beta]-phenyl-trioxybenzo-[gamma]-pyrone. Rhamnetin, a splitting product of the glucosides of _Rhamnus_, is monomethyl quercetin; fisetin, from _Rhus cotinus_, is monoxyquercetin; chrysin is phenyl-dioxybenzo-[gamma]-pyrone. Saponarin, a glucoside found in _Saponaria officinalis_, is a related compound. Strophanthin is the name given to three different compounds, two obtained from _Strophanthus Kombe_ and one from _S. hispidus_.
4. _Anthracene Derivatives._--These are generally substituted anthraquinones; many have medicinal applications, being used as purgatives, while one, ruberythric acid, yields the valuable dyestuff madder, the base of which is alizarin (q.v.). Chrysophanic acid, a dioxymethylanthraquinone, occurs in rhubarb, which also contains emodin, a trioxymethylanthraquinone; this substance occurs in combination with rhamnose in frangula bark.