Abstract
Using net assimilation rate as a measure of physiological activity, reciprocal transplants of Hylocomium splendens, Pleurozium schreberi and Racomitrium lanuginosum between Yläne (60°55′N) and Kevo (69°45′N) and between Kevo and Spitzbergen (78°13′N) were used to investigate adaptation to latitude. It was found that physiological stress increased northwards and that adaptation to different latitudes was largely due to acclimation. The importance of day length and temperature to mosses in extreme latitudes is discussed.