Reproduction by zoospores inOedogonium

Summary

Cell division in germlings and young filaments ofOedogonium is described. In one species, division proceeded as expected. The ring was formed at the apical wall weakening, and the basal cell did not divide again; the cap of wall derived from the basal cell was sometimes incorporated into the wall of the new apical cell. The second species showed significant differences. The “ring” laid down in the single-celled germling, and sometimes in the apical cell of a two-celled filament covered the whole apical end wall; the basal cell also usually underwent one more division, utilizing a normal ring.

It is suggested that the formation of rings for cell division represents an adaptation of a wound-response mechanism, brought into action by the deliberate creation of the circumferential weakening in the apical cell wall, and a concurrent increase in cell turgor. This proposal helps explain the divergent results above, and is further supported by the following examples, given in the paper: a) the frequent occurrence of accidental breaks in the wall, repaired sequentially by the deposition of amorphous and then layered wall material; b) a similar localized wall reinforcement invoked by the presence of rhizoids of other holdfasts attaching themselves to vegetative cells; c) a continuous layer of ring material being deposited over the entire end wall of a dividing cell, when the adjacent apical cell was empty; and d) the deposition of two rings in cells that had been previously treated with colchicine to prevent cytokinesis, and then been allowed to divide again.