Bornet[190] followed with his record of successful cultures. He selected for experiment the spores of _Physcia_ (_Xanthoria_) _parietina_ and was able to show that hyphae produced from the germinating spore adhered to the free-growing cells of _Protococcus[191] viridis_ and formed the early stages of a lichen thallus. Woronin[192] contributed his observations on the gonidia of _Parmelia_ (_Physcia_) _pulverulenta_ which he isolated from the thallus and cultivated in pure water. He confirmed the occurrence of cell division in the gonidia and also the formation of zoospores, these again forming new colonies of algae identical in all respects with the thalline gonidia. He was able to see the germinating tube from a lichen spore attach itself to a gonidium, though he failed in his attempts to induce further growth. In our own country Archer[193] welcomed the new views on lichens, and attempted cultures but with very little success. Further synthetic cultures were made by Bornet[194], Treub[195] and Borzi[196] with a series of lichen spores. They also were able to observe the first stages of the thallus. Borzi observed spores of _Physcia_ (_Xanthoria_) _parietina_ scattered among _Protococcus_ cells on the branch of a tree. The spores had germinated and the first branching hyphae had already begun to encircle the algae.
[Illustration: Fig. 5. _Endocarpon pusillum_ Hedw. Asci and spores, with hymenial gonidia × 320 (after Stahl).]
[Illustration: Fig. 6. _Endocarpon pusillum_ Hedw. Spore germinating in contact with hymenial gonidia × 320 (after Stahl).]
Additional evidence in favour of the theory of the independent origin of the colourless filaments and the green cells was furnished by Stahl’s[197] research on hymenial gonidia in _Endocarpon_ (Fig. 5). By making synthetic cultures of the mature spores with these bodies, he was able to observe not only the germination of the spores and the attachment of the filaments to the gonidia (Fig. 6), but also the gradual building up of a complete lichen thallus to the formation of perithecia and spores.
[Illustration: Fig. 7. Germination of spore of _Physcia parietina_ De Not. in contact with _Protococcus viridis_ Ag. × 950 (after Bornet).]