u 



species have been already described ^), those with (wo thinner ones 

 are still to be published. 



The species of Zygnema which I 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 

 I had previously used with good results in the case of Spirogyra 

 and other plants, namely, fixing with Flemmung's mixture and treating 

 with chromic acid. I moditied the method slightly so as to facilitate 

 the investigation of Zygnema. The many globules of fat in the 

 cytoplasm sometimes greatly hinder the investigation of the nuclei. 

 For this reason T tixed with absolute alcohol, then left the material 

 for some days in ether, transferred it again to absolute alcohol 

 and replaced this by distilled water. Finally the material was placed 

 in F],emming's mixture, in which it remained some days, until the 

 treatment with chromic acid yielded the desired result, namely, slow 

 solution of the cytoplasm and cliromato})hores and isolation of the 

 nucleus. The latter afterwards gradually dissolves, during which 

 process some of the more resistant parts become very clearly visible. 

 No contraction or coalescence of the protoplast should occur. 

 vShould this happen as the result of a faulty application of the method, 

 the material is useless. The strength of the chromic acid solution, which 

 I applied was 10 or 257o- Sometimes the chromic acid, when it had 

 acted sufficiently was washed out with distilled water and the prepa- 

 rations were stained blue by means of "Brilliantblau extra grUnlich". 



The preliminary ti-eatment with alcohol and ether was advantageous 

 and unaccompanied by any drawback. The troublesome fat was got 

 rid of and it seemed to me that the tixation of the nuclei in 

 Zii<jnema was even better than l)y the direct action of Flemming's 

 mixture. 1 did not see the cavity round tlie nucleolus, which Escoyez 

 named cavilé périnucléolaire, and regarding the existence of which 

 in the living object there are also differences of opinion in other 

 cases. Therefore 1 assume that no such cavity occurs in the living 

 material and tins agrees with the results I obtained previously with 

 other plants. 



Resting micleus. The nucleus is situated in the middle of the cell 

 between the two chromatophores and is stretched longitudinally. 

 The following parts can be distinguished in the resting nucleus: the 

 nuclear membrane, the network composed of small granular bodies 



1) C. VAN WissELiNGH, Uebei" tlen Nucleolus von Spirogyra, Bot. Zeitung 1898, 

 Heft Xl'XII, p. 195. — Ueber Keinteilung bei Spirogyra, Flora, 1900, 87. Bd. 

 4. Heft, p. 355. - Untersuchuogen über Spirogyra, Bot. Zeitung, f902. Heft VI, 

 p. 115. — Ueber abnormale Kernteilung, Bot. Zeitung, 1903, Heft X/XII p. 201. 



