Résumé : 1. 1. Removal of the nucleus has no effects on the oxygen consumption of the alga Acetabularia and little effect on the uptake of 32P. 2. 2. The morphology and the chemical composition of the nucleus undergo strong modifications when oxidative phosphorylations are inhibited. 3. 3. A clear protein and RNA synthesis is possible in non-nucleated pieces; this synthesis can even proceed at a faster rate in the non-nucleated halves than in the other, but it slows down later on. 4. 4. Incorporation of labelled precursors into proteins and RNA occurs, at a normal rate, during several months in non-nucleated cytoplasm. 5. 5. The meaning of these results is discussed. © 1955.