The Effects of Day‐length on the Development of the Sporophyte of Polytrichum Aloides Hedw. And P. Piliferum Hedw.

Summary The apical meristem of the sporophyte of Polytrichum spp. has been described briefly. The meristem is described as vegetative so long as it continues to contribute cells to the seta: in this vegetative phase the endothecium is a distinct histogen. In the reproductive phase all the cells in the meristem are used in the construction of the sporangium and the onset of this phase is marked by the segmentation of the endothecium from below upwards. Experiments with P. aloides Hedw. and P. piliferum Hedw. indicate that the development of the sporangium, once initiated, is conditioned by seasonal factors, but the transition from the vegetative to the reproductive phase is conditioned by some other factor(s) not identified. When the growth of a sporangium is inhibited by experimental conditions, vegetative growth is not prolonged.