Abstract
We reobtained juvenile lichen thalli from cultured fragments of natural thalli of Usnea rubescens and Peltigera praetextata in vitro. Both reformed lichen thalli in vitro were obtained under poor nutrition conditions. The thallus of cultured Peltigera praetextata was composed of both dorsal and ventral cortices and a medulla with Nostoc cells as a phycobiont. Both dorsal and ventral cortices, which were not attached to the agar medium, were paraplectenchymatous hyphal tissues. But, the ventral cortex, which was attached to agar media, was composed of rather undifferentiated plectenchymatous hyphal tissues. Various developmental stages of the cyanolichen thalli were observed under controlled laboratory conditions. Chages in the shape of Nostoc colonies were observed from a free-living filamentous stages to symbiotic cell aggregate stages. The transformation of Nostoc colonies may be controlled by a soluble chemical, because it was observed without direct contact of mycobiont hyphae.
