ABSTRACT
Early work on the photoperiodic responses of liverworts had shown a very clear induction of dormancy by long days in Lunularia cruciata, especially in the Mediterranean strains, while in short-day conditions growth of this species continued rapidly without interruption. An obvious requirement for an attempt is to devise a suitable bioassay method which will demonstrate the presence or absence of suspected inhibitory or other substance. For this purpose the gemmae were chosen as the most suitable material. Thalli which have been arrested in their growth by long-day treatment were found to exhibit resistance to drought. Lunularia thalli growing actively on a moist medium will desiccate and die if removed from the moist substrate and exposed to atmospheres of relative humidity less than 90%; i.e., their drought resistance is negligible. While there are clearly quantitative and probably also qualitative differences between species which so far have not been detected, the generalizations below must be regarded as almost certainly too sweeping.
