The Peristome of Anacamptodon splachnoides

The peristome of Anacamptodon splachnoides (Froel. ex Brid.) Brid. was studied with the aid of the light microscope and the scanning electron micro- scope. Contrary to recent accounts, the peristome of this moss conforms struc- turally to that expected of a reduced diplolepideous peristome and is, therefore, not exceptional. It possesses sixteen exostome teeth, each consisting of two layers of wall thickenings, an outer, strongly papillose, thickened lamella, composed of a double row of vertical plates and an inner lamella, which is thin, membranous and smooth, consisting of a single series of vertical plates. There are sixteen endostome segments located inside and alternating with the teeth. The segments are much reduced; each is essentially two cells wide and generally less than eight cells high. A fragmentary basal membrane is usually evident. The basic develop- mental pattern for diplolepideous peristomes is discussed. The outer peristome teeth of diplolepideous mosses traditionally have been thought to consist uniformly of two plies of wall thickenings, an outer lamella composed of a double series of vertical plates and a single series of inner ones. Buck and Crum (1978), however, described the exostome teeth of Anacamptodon splachnoides (Froel. ex Brid.) Brid., as consisting of a single layer that is papillose on both surfaces. The inner layer, according to them, is missing, an interpretation that more recently has been reemphasized by Buck (1980). Even more remarkable are the observations by the same authors that the endostome segments arise ". . . between the pairs of teeth, seemingly at the same plane as the ex- ostome, rather than behind it." These descriptions of the peristome structure of this moss are so unusual and differ so radically from previous accounts of basic peristome develop- ment that it seemed desirable to carry out additional studies utilizing both the light micro- scope and the scanning electron microscope (SEM).