False colour scanning electron micrograph of the lichen Xanthoria parietina,showing a fruiting body or apothecium (spore bearing),growing out of the thallus (vegetative part). Lichens are symbiotic organisms,consisting of an algal & a fungal partner. The fungus benefits from the photosynthetic activity of the alga. The advantage to the alga,although not clear,may lie in protection from drought & intense light. Slow growing organisms (1-2mm per year),they live to immense ages,colonising tree trunks,soil,rock,& mortar. Lichens are sensitive to sulphur dioxide & hence used to monitor air pollution. Magnification: X31 at 35mm size. Original is bw print B350/005 |