Observation of replicas of freeze-etched spore mother cells ofPsilotum nudum(L.) Beauv. has shown that the nuclear envelope undergoes remarkable changes on passing from premeiotic to meiotic stages. Before meiosis, the nuclear envelope shows an even surface covered by randomly distributed pores, whereas in leptotene-zygotene it becomes uneven and wave-like while the pores progressively gather in separate clusters. As a result, wide portions of nuclear envelope devoid of pores are observed at this stage. It is suggested that such events could be originated by traction forces acting on the inner membrane, at early stages of meiosis, and due to motions of the attached chromosome fibers in the course of spiralization and pairing processes. The decrease in average pore frequency in leptotene- zygotene, as compared to the premeiotic stages, is also related, as a first assumption, to the aforementioned traction forces. Quite similar phenomena to those reported forPsilotum nudum(L.) Beauv. were also observed inArisarum proboscideum(L.) Savi during microsporegenesis.