Morphogenesis in Micrasterias. II. Patterns of morphogenesis.

The final form of the polar lobe and lateral wings of developing semicells of M. rotata results from combined action of three growth processes: tip growth, branching and lobe broadening. Tip growth unaccompanied by branching or broadening occurs during normal development in M. radiata, but is observed only under abnormal conditions (e.g. raised temperature) in M. rotata. When branching and broadening do occur, they occur together and for this reason may be causally related. Autoradiograms demonstrate that specific patterns of cell wall incorporation can be associated with each of the three processes in M. rotata. Autoradiographic patterns found in the polar lobe differ from those found in wings. The growing polar lobe also responds to laser irradiation differently from the wings; lasings occasionally cause duplication of the polar lobe.