Thallus growth and the distribution of stored metabolites in the phycobionts of the lichens Parmelia sulcata and P. physodes

The growth of two lichens, Parmelia sulcata and P. physodes, has been examined under controlled conditions. It has been shown that continuous light leads to early death of both lichens. Evidence from fine structure work following pretreatment of the lichen thallus with different levels of thallus saturation indicates that fluctuating wet and dry conditions are also vitally necessary for continued thallus growth. This is explicable in terms of the relative mobility of fixed carbon from the algal component at different levels of thallus saturation.