Acharius[477] gave the name “soredia” to the powdery bodies with reference to their propagating function; he also interpreted the soredium as an “apothecium of the second order.” But long before his time they had been observed and commented on by succeeding botanists: first by Malpighi[478] who judged them to be seeds, he having seen them develop new plants; by Micheli[479] who however distinguished between the true fruit and those seeds; and by Linnaeus[480] who considered them to be the female organs of the plant, the apothecia being, as he then thought, the male organs. Hedwig[481], on the other hand, regarded the apothecia as the seed receptacles and the soredia as male bodies. Sprengel’s[482] statement that they were “a subtile germinating powder mixed with delicate hair-like threads which take the place of seeds” established finally their true function. Wallroth[483], who was the first really to investigate their structure and their relation to the parent plant, recognized them as of the same type as the “brood-cells” or gonidia; and as the latter, he found, could become free from the thallus and form a green layer on trees, walls, etc., in shady situations, so the soredia also could become free, though for a time they remained attached to the lichen and were covered by a veil, _i.e._ by the surrounding hyphal filaments. Koerber[484] also gave much careful study to soredia, their nature and function. As propagating organs he found they were of more importance than spores, especially in the larger lichens. [Illustration: Fig. 81. Vertical section of young soralium of _Evernia furfuracea_ var. _soralifera_ Bitter × 60 (after Bitter).] According to Schwendener[485], the formation of soredia is due to increased and almost abnormal activity of division in the gonidial cell; the hyphal filament attached to it also becomes active and sends out branches from the cell immediately below the point of contact which force their way between the newly divided gonidia and finally surround them. A soredial “head” of smaller or larger size is thus gradually built up on the stalk filament or filaments, and is ultimately detached by the breaking down of the slender support.