The Ultrastructure of the Meristoderm Cells of the Hapteron ofLaminaria

This investigation of the ultrastructure of the cells of laminarian haptera is part of a more detailed study of the growth of marine macroalgae and their inter-action with the environment. A major section of the programme is an attempt to establish the relationships between physiological, biochemical and structural (including ultrastructural) changes which occur during cell growth in brown algae and to compare such observations with those recorded for higher plant cells. The choice of haptera (PI. IA) for much of this work on brown algal cell growth is based on their suitability for the interpretation of enzymological data on a cellular basis. Hapteron growth shows several convenient similarities to that in primary meristems of higher plants. Although lamina growth is from an intercalary meristem at the base of the lamina (transition zone), hapteron growth is essentially apical (Reinke, 1876), and differentiating cells are arranged in rows leading backwards from the apex (PI. IB, c). Thus, progressive sections cut from the tip backwards will contain an increasing percentage of vacuolate, elongating cells, as in the flowering plant root.