The best known Hymenolichen, _Cora Pavonia_ (Fig. 86), was discovered by Swartz[516] during his travels in the W. Indies (1785-87) growing on trees in the mountains of Jamaica, and the new plant was recorded by him as _Ulva montana_. Gmelin[517] also included it in _Ulva_ in close association with _Ulva_ (_Padina_) _Pavonia_, but that classification was shortly after disputed by Woodward[518] who thought its affinity was more nearly with the fungi and suggested that it should be made the type of a new genus near to _Boletus_ (_Polystictus_) _versicolor_. Fries[519] in due time made the new genus _Cora_, though he included it among algae; finally Nylander[520] established the lichenoid character of the thallus and transferred it to the Lecanorei. It was made the subject of more exact investigation by Mattirolo[521] who recognized its affinity with _Thelephora_, a genus of Hymenomycetes. Later Johow[522] went to the West Indies and studied the Hymenolichens in their native home. The genera and species described by Johow have been reduced to _Cora_ and _Dictyonema_; a new genus _Corella_ has since been added by Wainio[523]. Johow found that _Cora_ grew on the mountains usually from 1000 to 2000 ft. above sea-level. As it requires for its development a cool damp climate with strong though indirect illumination, it is found neither in sunny situations nor in the depths of dark woods. It grows most freely in diffuse light, on the lower trunks and branches of trees in open situations, but high up on the stem where the vegetation is more dense. It stands out from the tree like a small thin bracket fungus, one specimen placed above another, with a dimidiate growth similar to that of _Polystictus versicolor_. Both surfaces are marked by concentric zones which give it an appearance somewhat like _Padina Pavonia_. These zones indicate unequal intercalary growth both above and below. The whole plant is blue-green when wet, greyish-white when dry, and of a thin membranaceous consistency. B. STRUCTURE OF THALLUS There is no proper cortex in any of the genera, but in _Cora_ there is a fastigiate branching of the hyphae in parallel lines towards the upper surface; just at the outside they turn and lie in a horizontal direction, and, as the branching becomes more profuse, a rather compact cover is formed. The gonidia, which consist of blue-green _Chroococcus_ cells, lie at the base of the upward branches and they are surrounded with thin-walled short-celled hyphae closely interwoven into a kind of cellular tissue. The medulla of loose hyphae passes over to the lower cortex, also of more or less loose filaments. The outermost cells of the latter very frequently grow out into short jagged or crenate processes (Fig. 87).