On the nucleolus and karyokinesis in Zygnema. Ninth contribution to the kwowledge of karyokinesis

Whilst Spirogyra has very often been used for the investigation of the nucleus and nuclear division, Zygnema has so far as I know, up to the present, only been studied for this purpose by two investigators. It should be no cause for surprise that the latter alga has generally been neglected. The dimensions of the cells and nuclei are so much smaller than those in the larger species of Spirogyra, that one would expect to meet with still greater difficulties in a karyokinetic investigation than would arise in the case of Spirogyra. Such is indeed the case and in studying karyokinesis I have not been able to trace the details of the process to the same extent as in different species of the genus Spirogyra. Mabel L. Merriman1) was the first to study karyokinesis in Zygnema. She could not with certainty identify the species studied, because she had no zygospores at her disposal. The chief results of her inquiry were as follows.