CELL DIVISION IN BULBOCHAETE. I. DIVISIONS UTILIZING THE WALL RING1

Cell division in Bulbochaete closely resembles that of Oedogonium, particularly in the involvement of a ring in cell elongation, the structure of the spindle, the existence of complex kinetochores, and the method of cross-wall formation using a phycoplast. Some minor differences between the 2 genera are found. In contrast to Oedogonium, the filaments of Bulbochaete are branched. The site and direction of branching are initially determined by a subtle change in the morphology of the wall, which invariably (if the cell divides) leads to the asymmetrc division that forms a hair cell (these events will be described separately). The position of the wall ring is always precisely determined as in Oedogonium, by the position of a very characteristic weakening in the wall; once a hair cell has been formed, this weakening is located underneath the hair, and all subsequent division and elongation in the cell subtending the hair will necessarily be in the direction of that hair (ie, thereby forming and increasing the length of a branch).