Very shortly after, Von Flotow[163] published his views on some other lichen gonidia. He had come to the conclusion that the various species of the alga, _Gloeocapsa_, so frequently found in damp places, among mosses and lichens, were merely growth stages of the gonidia of _Ephebe pubescens_, and bore the same relation to _Ephebe_ as did _Lepra viridis_ (_Protococcus_) to _Parmelia_. The gonidium of _Ephebe_ is the gelatinous filamentous blue-green alga _Stigonema_ (Fig. 4), and the separate cells are not unlike those of _Gloeocapsa_. Flotow had also demonstrated that the same type of gonidium was enclosed in the cephalodia of _Stereocaulon_. Sachs[164], too, gave evidence as to the close connection between _Nostoc_ and _Collema_. He had observed numerous small clumps of the alga growing in proximity to equally abundant thalli of _Collema_, with every stage of development represented from one to the other. He found cases where the gelatinous coils of _Nostoc_ chains were penetrated by fine colourless filaments “as if invaded by a parasitic fungus.” Later these threads were seen to be attached to some cell of the _Nostoc_ trichome. Sachs concluded, however, from very careful examination at the time, that the colourless filaments were produced by the green cells. As growth proceeded, the coloured _Nostoc_ chains became massed towards the upper surface, while the colourless filaments tended to occupy the lower part of the thallus. He calculated that during the summer season the metamorphosis from _Nostoc_ to a fertile _Collema_ thallus took from three to four months. He judged that in favourable conditions the change would inevitably take place, though if there should be too great moisture no _Collema_ would be formed. His study of _Cladonia_ was less successful as he mistook some colonies of _Gloeocapsa_ for a growth condition of _Cladonia_ gonidia, an error corrected later by Itzigsohn[165]. [Illustration: Fig. 4. _Ephebe pubescens_ Nyl. Tip of lichen filament × 600.] But before this date Itzigsohn[166] had published a paper setting forth his views on thallus formation, which marked a distinct advance. He did not hazard any theory as to the origin of gonidia, but he had observed spermatia growing, much as did the cells of _Oscillaria_: by increase in length, and, by subsequent branching, filaments were formed which surrounded the green cells; these latter had meanwhile multiplied by repeated division till finally a complete thallus was built up, the filamentous tissue being derived from the spermatia, while the green layer came from the original gonidium. In contrasting the development with that of _Collema_, he represents _Nostoc_ as a sterile product of a lichen and, like the gonidia of other lichens, only able to form a lichen thallus when it encounters the fructifying spermatia.