Braxton Hicks[167], a London doctor, some time later, made experiments with _Chroococcus_ algae which grew in plenty on the bark of trees, and followed their development into a lichen thallus. He further claimed to have observed a _Chlorococcus_, which was associated with a _Cladonia_, divide and form a _Palmella_ stage. C. CULTURE EXPERIMENTS WITH THE LICHEN THALLUS It had been repeatedly stated that the gonidia might become independent of the thallus, but absolute proof was wanting until Speerschneider[168], who had turned his attention to the subject, made direct culture experiments and was able to follow the liberation of the green cells. He took a thinnish section of the thallus of _Hagenia_ (_Physcia_) _ciliaris_, and, by keeping it moist, he was able to observe that the gonidial cells increased by division; the moist condition at the same time caused the colourless filaments to die away. This method of investigation was to lead to further results. It was resorted to by Famintzin and Baranetzky[169] who made cultures of gonidia extracted from three different lichens, _Physcia_ (_Xanthoria_) _parietina_, _Evernia furfuracea_ and _Cladonia_ sp. They were able to observe the growth and division of the green cells and, in addition, the formation of zoospores. They recognized the development as entirely identical with that of the unicellular green alga, _Cystococcus humicola_ Naeg. Baranetzky[170] continued the experiments and made cultures of the blue-green gonidia of _Peltigera canina_ and of _Collema pulposum_. In both instances he succeeded in isolating them from the thallus and in growing them in moist air as separate organisms. He adds that “many forms reckoned as algae, may be considered as vegetating lichen gonidia such as _Cystococcus_, _Polycoccus_, _Nostoc_, etc.” Meanwhile Itzigsohn[171] had further demonstrated by similar culture experiments that the gonidia of _Peltigera canina_ corresponded with the algae known as _Gloeocapsa monococca_ Kütz., and as _Polycoccus punctiformis_ Kütz. D. THEORIES AS TO THE ORIGIN OF GONIDIA