INDEPENDENCE OF ORGANOGENESIS AND CELL PATTERN IN DEVELOPING ANGLE SHOOTS OF SELAGINELLA-MARTENSII

Angle meristems are mounds of meristematic tissue located at dorsal an d/or ventral branch points of the dichotomising stem axes of many spec ies of Selaginella (Lycophyta). The present study examined the develop ment of ventral angle shoots of S. martensii in response to removal of distal shoot apices (decapitation). Scanning electron microscopy of s equential replicas of developing angle meristems and angle shoots reve aled that for the first two pseudowhorls of leaf primordia, particular leaves are not attributable to particular merophytes of the angle mer istem apical cell. Individual leaf primordia of the first (outer) pseu dowhorl often form from more than one merophyte. Neither the shape of the angle meristem apical cell nor the direction of segmentation has a ny effect on the development of the angle shoot. Additionally, the api cal cell of the angle meristem does not necessarily contribute directl y to either of the new shoot apices of the developing angle shoot. The first bifurcation of the angle shoot shows a remarkably consistent re lationship to the branching pattern of the parent shoot. The strong br anch of the first angle shoot bifurcation of the young angle shoot inv olved the formation of two new growth centres some distance away from the original angle meristem apical cell; new apical cells subsequently formed within these. These results provide additional support for the view that cell lineage has little or no effect on final form or struc ture in plants.