Fig. 1

Clusters of antheridia on a Physcomitrella gametophore (some leaves were removed). a A cluster of open, empty antheridia on the stem close to the apex and a cluster of closed antheridia at the apex which is suitable for the observation of sperms (arrow). b, c Magnification of the clusters of closed (b) and open (c) antheridia. Scale bars 500 µm in a; 50 µm in b and c