Olive, Mitotic division of tlie nuclei of the Cyanophyceae. 13 



tlie Botanical Grarden of Harvard University, and tlie otlier 

 species from tlie Botanical Grarden of the University of Bonn; 

 or from ponds in the neighborhood of Bonn. Five species of 

 Oscülatoria, and one sj^ecies each of Phormidium, Calothrix^ 

 Nostoc, GJoPOcapsa, and Cylindrospennum, have been studied. 



But two methods of fixation have been generally employed; 

 viz., Flemming's weaker solntion, and St ras bürg er' s modi- 

 fication of Flemming's mixtiu^e, sometimes called the ,.niiddle 

 Solution". The SOo-alcohol niixture, recommended by Hegler, 

 gives, as he asserts, a sharply marked central body, but I have 

 found that the nuclei so treated are unnaturally shrunken, and 

 that the whole cell is frequently plasmolized (see figs. 2, 3), 

 hence I early abandoned this method. After fixation, the masses 

 of filaments were washed for a few houi's in water, then dehy- 

 drated by passing through the usual grades of alcohols. They 

 were then carried through Chloroform or xylol, successively 

 infiltrated with paraffine melting at 52" and 60", and iinally 

 sectioned 1 — 4 ^w thick. The mucli employed stains, Flemming's 

 safranin, gentian violet, with or without orange Gr, and Hei den - 

 hain's iron haematoxyhn, sometimes followed by eosin or orange, 

 gave most excellent results. For certain purposes, a mixture of 

 metliyl blue and eosin, or of methylene blue and eosin, was 

 used: and a few other stains were tried, but none were so 

 satisfactor}'- for the nuclear Clements as the two Standard stains 

 mentioned above. 



In studying the preparations, a glass globe filter and con- 

 denser, filled with a liglit blue Solution of ammoniated copper 

 sulphate, was used, in connection with a Welsbach gas lamp. 

 So far as the writer has been able to discover, only three 

 investigators have so far attempted to cut sections of tliese 

 plants — Hegler, Fischer, and Wager. A thorough exami- 

 nation of the Hegler preparations, loaned me through the 

 kindness of Professor G. Karsten, have convinced me that his 

 sections of Axabaoia were entü-ely too thick to enable him 

 to discover from tliem much that w^as new. His preparations 

 show, as do also the photogravures illustrating his exhaustive 

 article, a central Ijody which is so deeply stained that chromatic 

 and achromatic substances can not be clistinguished from each 

 other. Judging, however, from the text, Hegler must have seen 

 clearly the chromatin granules lying in the aclu'omatic portion 

 of the central body, as his description of tliem sliows. 



Fischer 's drawings show that his cross sections of Oscil- 

 Icdoria must have been excellent and some, at least, well stained. 

 He gives but two drawings of longitudinal sections of Oscillatoria, 

 both stained with Delafield's haematoxylin, figure 42 showing 

 the slime globules, or .,red granules" of Bütschli, lying iiu- 

 bedded in the central body, and ligure 49, showing simply tlin 

 deeply stained central body alone. It may assist us in tinding 

 a reason for Fischer" s decision against the nuclear nature of 

 the central body by comparing liis tigure 36 with figm'e 18 of 



