Printed in Great Britain ON MITOSIS IN THE MULTICELLULAR ALGA

Mitosis has been studied in the multicellular green alga Ulva mutabilis by light microscopy and by electron microscopy. Mitosis seems to be of the classical type with regard to spindle, centrioles and continuous and chromosomal microtubules. The nuclear membrane, however, disappears only at the poles and persists as a boundary around the mitotic apparatus. In this respect the Ulva cell seems to be in an intermediate position between those species which have intranuclear mitosis and the forms where the nuclear membrane breaks down. A hypothesis which involves localized synthesis of membranes explains partly the intracellular rearrange-ment of nucleus, Golgi region and chloroplast after mitosis