Morphogenetic determination of the axial cells of Antithamnion plumula (ceramiaceae, rhodophyta) : early identification of the nature of the whorls

Antithamnion plumula axial cells are either "cladomophoric" (bearing a lateral cladom) or "pleuridiophoric" (with pleuridia only). The time required for their formation (generation time) and their length were the two variables used for their early characterization. The data presented show that (i) the generation time (approximately 10 h) of the pleuridiophoric axial cell, which immediately succeeds a cladomophoric axial cell, is significantly longer than that observed for all the other axial cells (6–7 h); (ii) the initial cell length (approximately 9 μm) of the cladomophoric axial cells is significantly greater than that of the pleuridiophoric axial cells (approximately 6 μm); and (iii) during the first stages of cell elongation (when the distance to the apex does not exceed 12 cells), the difference in size between the axial cells remains significant; the lateral budding of the cladomophoric cell occurs earlier than that of the pleuridiophoric cell. Thus, the cladomophoric axial cells can be distinguish...