Spore development and germination in Cinclidium (Mniaceae, Bryophyta), with special reference to spore mortality and false anisospory

Abstract

Spores of Cinclidium arclicum (B.S.G.) Schimp., C. stygimn Sw., and C. subrotundum Lindb. pass through five phases of development from meiosis to protonema formation: tetrad phase, perine formation phase, stationary phase, swollen phase, and distension phase. They are shed from the sporangium at the termination of the swollen phase and show all characters diagnostic to the first phase of germination of spores of Funaria hygrometrica and Ceratodon purpureus. At the swollen phase, and as a contrast to spores at the three first phases of the sporogenesis, the spores of Cinclidium behave like a population of unicellular plants which grow under conditions with still decreasing quantities of liquid available for continued expansion.In Cinclidium, spore mortality occurs during the stationary phase, but otherwise, lethal factors appear to be independent of general spore development. For Cinclidium arcticum and C. stygium, spore mortalities of 50% generally occur, which can be explained by a genetic system based on the presence of two differentiating genes, each of which consists of a dominant and a recessive allele.False anisospory, here proposed as a new term, is present in a sporangium when the spore mass consists of both smaller dead spores and relatively larger living spores. It occurs in the three species of Cinclidium studied. False anisospory is caused by the death of a fraction of the spore mass during an intermediate stage of sporogenesis and the maturation of the remaining fraction to the subsequent swollen stage.It is probable that one of the two differentiating genes responsible for the false anisospory and the 50% spore mortality in Cinclidium arcticum and C. stygium is located in the sex chromosome, while the other gene is located in one of the autosomes. Since Cinclidium arcticum, n = x = 7, is dioecious and C. stygium, n = 2x = 14, is monoecious, false anisospory is independent of sexuality and the level of ploidy.