Printed in Great Britain AUTORADIOGRAPHIC EVIDENCE FOR THE RAPID DISINTEGRATION OF ONE CHLOROPLAST IN THE ZYGOTE OF THE

This paper gives evidence suggesting that one of the two chloroplasts contributed to the zygote of Ulva mutabilis is rapidly destroyed. Chloroplasts in an advanced stage of disintegra-tion can be seen only 4 min after copulation. Radioactive labelling of gametes prior to copulation shows that the disintegrating chloroplast is supplied through the + (plus) gamete, while the chloroplast from the — (minus) gamete is retained in the zygote. These observations are in agreement with genetic observations from the same alga