Developmental Anatomy of the Marsupium in Calypogeia

Abstract

The marsupium of Calypogeia trichomanis (L.) Corda originates as an archegonial branch, ventrally, from a prostrate vegetative stem. It early curves laterally, due to meristemnatic activity on one side of the branch. Further refinement and activity of this meristem cause a cuplike sheath (the marsupium) to rise about the archegonial receptacle. The elongating marsupium burrows into the substrate, carrying the enclosed archegonia and subsequent sporophyte with it. Initiation of the eccentric growth of the branch and establishment of the marsupial form occur before fertilization. The architecture of the meristematic tissue and of the marsupial form is unlike that of any other structure in the plant body, and is indicative of the diverse potentialities of the plant's genotype. In the leafy liverworts, one of the more notable features is the gametophoric structure that encircles, one way or another, the early growth of the sporophyte. Most typically, the structure is a fusion of the uppermost two or three leaves (the perianth) about the archegonial receptacle. More complex forms involve extensions of the stem tissue, and the most complex of these, occurring in more than a dozen genera, is the marsupium. In its strongest expression, the marsupium is an elongate, sac-shaped organ, thicker in diameter than the prostrate stem from which it arose, and extending down into the substrate. The base of the marsupium encloses the maturing archegonia and the young sporophyte; the top is open, allowing the maturing sporophyte to emerge above the substrate. Because the internal, basal position of the archegonia (and subsequent sporophyte) indicates that the marsupium results from an eccentric development of an archegonial branch, the development in several species has been studied for more than a century. According to Knapp (1930), the first serious study was by Gottsche (1845). Aside from Knapp's own lengthy analyses, the main reviews of the present century came from Goebel (1906), Cavers (1911), and Schuster (1966). In particular, a detailed study of the marsupium in Geocalyx has been given by Knapp (1930), and comparable studies in Calypogeia have been done by Ellwein SDepartment of Biological Sciences, State University, Plattsburgh, New York 12901. This content downloaded from 157.55.39.153 on Mon, 19 Sep 2016 04:48:09 UTC All use subject to http://about.jstor.org/terms 1969 NOLAN: DEVELOPMENT OF THE MARSUPIUM IN CALYPOGEIA 215 (1926) and Douin (1929). The present paper offers additional details on the developmental anatomy of the marsupium in Calypogeia and should clarify some questions about the meristematic centers of the marsupium and about the timing of development, relative to fertilization and embryogeny. MATERIALS AND METHODS All stages of development reported in this paper come from one clump of Calypogeia trichomanis (L.) Corda collected 13 December 1967 in the northern foothills of the Adirondack Mountains, Clinton County, New York. The material was fixed in FPA, dehydrated in the regular tertiary butyl alcohol series, embedded in Tissuemat, sectioned at 7-10t, and stained according to the celestine blue B-safranin schedule of Gray and Pickle (1956) with fast green counterstain. Stages not reported in this paper, but found in the collection, include mature marsupia about 1 cm long, containing sporophytes with post-sporogenesis capsules but with setae not yet exserted.