STUDIES IN THE PHYSIOLOGY OF LICHENS

Summary A method for directly isolating cells of the algal symbiont (Nostoc) in quantity from the thallus of Peltigera polydactyla is described. Such directly isolated algae excrete much of the photosynthetically fixed carbon into the medium as glucose, but they lose this property after only 48 hours in culture, at which time the cells begin to release only small amounts of a compound which may be a polysaccharide. These results are discussed in the context of the transfer of fixed carbon from alga to fungus in the lichen thallus during photosynthesis. After the lichen algae had been in pure culture for some time, they showed a carbohydrate metabolism intermediate in a number of respects between the directly isolated Nostoc and a strain of free‐living N. muscorum. All three kinds of algae were able to utilize externally supplied glucose. The Nostoc from lichens could not utilize mannitol.