THE APICAL MERISTEM OF FUCUS

Summary Studies on young vegetative apices of Fucus show that after the large apical cell is differentiated it becomes surrounded by an extensive meristematic zone, the pro‐meristem. It is suggested that this is the main zone of cell division at the apex and that the apical cell itself rarely segments. But the apical cell is the main seat of control, for without it the apex shows no further growth. The size of the apical cell and of the pro‐meristem increases during growth of the vegetative branch. A new apical cell becomes associated with a portion of the pro‐meristem when forking of a branch occurs. Morphologically there is sudden change from vegetative to reproductive growth at an apex. Apical initials and a pro‐meristem function in a receptacle until all concept‐acles are laid down. Following conceptacle development there is a loss of meristematic activity at the apex, and after gamete discharge the tissues gradually disintegrate.