Studies in the Physiology of Lichens: With two Figures in the Text

Discs cut from the thallus of the lichen Peltigera polydactyla contain relatively large amounts of ammonia nitrogen and small amounts of amide nitrogen. During starvation in the dark the amounts of ammonia and amide nitrogen remain unchanged, but the amount of amino-nitrogen increases. Absorption of ammonia results in increases in the amounts of ammonia and amino-nitrogen in the discs, but not in the amount of amide nitrogen. It is therefore concluded that amides do not have an important quantitative role in the nitrogen metabolism of the discs. Ammonia absorption is stimulated by addition of glucose to the medium, but the very slow rate of protein synthesis is only slightly increased by glucose. The rate of nitrate absorption is much slower than that of ammonia absorption. The ecological implications of the results are discussed, and existing knowledge of the nitrogen metabolism of lichens is reviewed.