‖ mesophlœumBot.|mɛsəʊˈfliːəm| [mod.L., f.Gr. µέσο-ς middle + ϕλοιός bark.] The middle layer of the bark in exogens. 1839Lindley Introd.Bot. i. ii. (ed. 3) 89 The Mesophlœum of Link, or cellular integument of others, composed of cells, usually green.