INDUCTION OF CELL DIFFERENTIATION IN DISSOCIATED CELLS AND FRAGMENTS OF CALLITHAMNION ROSEUM

Branching in regenerates of Callithamnion roseum is a phenomenon of cellular differentiation. Starting from single cells or filaments, a gradual morphological change in cell types occurs: from parallel cross-walled, branchless stalk cells to oblique cross-walled, branch-bearing main axis cells. The development of a plating technique and a synthetic sea water medium permits quantitative study of cell differentiation (or branching) in populations of regenerating cells or fragments. The distribution of regenerating fragments on a given plate is non-random as seen from the fact that it does not conform to the Poisson series. Clustering and attachment of neighboring fragments increases the likelihood of branch initiation. The change with age in the distribution of plated regenerating fragments is presented. Developmental potentialities of 5 fragment types were examined. Each fragment type could give rise to branching regenerates. Although apical fragments composed of more than 10 cells usually branched first in a plate, single, large, basal cells seem to have a greater regenerative capacity than do small apical fragments.