The effect of the calyptra on the plane of guard cell mother cell division in Funaria and Physcomitrium capsules
by French J. C., Paolillo D. J., Jr. (1975)
in Ann. Bot. 39: 233–236 – https://doi.org/10.1093/oxfordjournals.aob.a084936 –
Removal of the calyptra from an elongating sporophyte leads to seta thickening prior to capsule expansion and an essentially random orientation of stomata.
If the calyptra is removed from a sporophyte of Funaria at the time the division of the guard cell mother cells is expected, guard cells of abnormal shape and undivided guard cell mother cells are found in unusually high frequency.