Though the relationship between the gonidia within the thallus and free-living algal organisms seemed to be proved beyond dispute, the manner in which gonidia first originated had not yet been discovered. Bayrhoffer[172] attacked this problem in a study of foliose and other lichens. According to his observations, certain colourless cells or filaments, belonging to the “gonimic” layer, grew in a downward direction and formed at their tips a faintly yellowish-green cell; it gradually enlarged and was at length thrown off as a free globose gonidium, which represented the female cell. Other filaments from the “lower fibrous layer” of the thallus at the same time grew upwards and from them were given off somewhat similar gonidia which functioned as male cells. His observations and deductions were fanciful, but it must be remembered that the attachment between hypha and alga in lichens is in many cases so close as to appear genetic, and also it often happens that as the gonidium multiplies it becomes free from the hypha. In his _Mémoire sur les Lichens_, Tulasne[173] described the colourless filaments as being fungal in appearance. The green cells he recognized as organs of nutrition, and once and again in his paper he states that they arose directly by a sort of budding process from the medullary or cortical filaments, either laterally or at the apex. This apparently reasonable view of their origin was confirmed by other writers on the subject: by Speerschneider[174] in his account of the anatomy of _Usnea barbata_, by de Bary[175], and by Schwendener[176] in their earlier writings. But even while de Bary accepted the hyphal origin of the gonidia, he noted[177] that, accompanying _Opegrapha atra_ and other Graphideae, on the bark were to be found free _Chroolepus_ cells similar to the gonidia in the lichen thallus. He added that gonidia of certain other lichens in no way differed from _Protococcus_ cells; and as for the gelatinous lichens he declared that “either they were the perfect fruiting form of Nostocaceae and Chroococcaceae—hitherto looked on as algae—or that these same Nostocaceae and Chroococcaceae are algae which take the form of _Collema_, _Ephebe_, etc., when attacked by an ascomycetous fungus.” All these investigators, and other lichenologists such as Nylander[178], still regarded the free-living organisms identified by them as similar to the green cells of the thallus, as only lichen gonidia escaped from the matrix and vegetating in an independent condition.