4 
those of Miss Merriman and also from those of Berghs 
obtained with Spirogyra. 
With regard to the latter, [| remark, that the opinions 
of investigators on the nucleolus and karyokinesis of 
Spirogyra are very divergent and that weighty objections 
can be advanced against the conclusions of Berghs in 
particular 1). 
The object of my own inquiry was to answer the 
question concerning the agreement of the two genera in 
respect of the nucleoli and karyokinesis, of which I had 
already made a complete study in five species of Spirogyra. 
The results obtained with three thick species have been 
already described *), those with two thinner ones are still 
to be published. 
The species of Zygnema which Ï examined and of 
which I also had the zygospores, I identified as Zygnema 
cruciatum. 
The method of investigation was mainly the same as 
that which ÎI had previously used with good results in 
the case of Spirogyra and other plants, namely, fixing 
with Flemming's mixture and treating with chromic acid. 
[ modified the method slightly so as to facilitate the inves- 
tigation of Zygnema. The many globules of fat in the 
cytoplasm sometimes greatly hinder the investigation of 
the nuclei. For this reason I fixed with absolute alcohol, 
then left the material for some days in ether, transferred 
it again to absolute alcohol and replaced this by distilled 
1) C. van Wisselingh, Ueber die Karyokinese bei Oedogonium. 
Beïhefte zum Botan. Centralblatt. Bd. XXIII (1907), Abt. I. pag. 152 
and foll. 
2?) C. van Wisselingh, Ueber den Nucleolus von Spirogyra. Bot. 
Zeitung 1898, Heft XI/XII, p. 195. — Ueber Kernteilung bei Spirogyra. 
Flora, 1900, 87. Bd. 4. Heft, p. 355. — Untersuchungen über Spirogyra. 
Bot. Zeitung, 1902, Heft VI, p. 115. — Ueber abnormale Kernteilung, 
Bot. Zeitung, 1903, Heft X XII p. 201. 
