Nylander[1002] regarded the Stictaceae as the most highly developed of all lichens, and they easily take a high place among dorsiventral forms, but it is generally conceded that the fruticose type is the more highly organized. In any case they are the highest reach of the phylum or phyla that started with Pyrenopsidaceae and Collemaceae; the lowly gelatinous thalli changing to more elaborate structures with the abandonment of the gelatinous algal sheath, as in the Pannariaceae, and with the replacement of blue-green by bright-green gonidia. Reinke[1003], considers the Stictaceae as evolved from the Pannariaceae more directly from the genus _Massalongia_. Their relationship is certainly with Pannariaceae and Peltigeraceae rather than with Parmeliaceae; these latter, as we shall see, belong to a wholly different series. D. EVOLUTION OF ARCHILICHENS The study of Archilichens as of Phycolichens is complicated by the many different kinds of fungi and algae that have entered into combination; but the two principal types of algae are the single-celled _Protococcus_ group and the filamentous _Trentepohlia_: as before only the broad lines of thalline development will be traced. The elementary forms in the different series are of the simplest type—a somewhat fortuitous association of alga and fungus, which in time bears the lichen fructification. It has been stated that the greatest advance of all took place with the formation of a cortex over the primitive granule, followed by a restricted area of growth outward or upward which resulted finally in the foliose and fruticose thalli. Guidance in following the course of evolution is afforded by the character of the fructification, which generally shows some great similarity of type throughout the different phyla, and remains fairly constant during the many changes of thalline evolution. Development starting from one or many origins advances point by point in a series of parallel lines. _a._ THALLUS OF PYRENOCARPINEAE. In this series there are two families of algae that function as gonidia: Protococcaceae, consisting of single cells, and Trentepohliaceae, filamentous. _Phyllactidium_ (_Cephaleuros_) appears in a single genus, _Strigula_, a tropical epiphytic lichen. Associated with these types of algae are a large number of genera and species of an elementary character, without any differentiation of tissue. In many instances the thallus is partly or wholly embedded in the substratum. Squamulose or foliose forms make their appearance in Dermatocarpaceae: in _Normandina_ the delicate shell-like squamules are non-corticate, but in other genera, _Endocarpon_, _Placidiopsis_, etc., the squamules are corticate and of firmer texture, while in _Dermatocarpon_, foliose fronds of considerable size are formed. The perithecial fruits are embedded in the upper surface.