404 BOTANICAL GAZETTE [JUNE 
at the center of the nucleus, which seemed to take the place of the 
nucleus or nucleoli of other plants. 
All of this work on Closterium, with the exception of my in- 
vestigation, it will be noted has been done either on the living 
cells or on fixed and stained whole mounts. The only members 
of the Conjugatae that have been studied with reference to cell . 
and nuclear division in sectioned material are Spirogyra and 
Zygnema. Many investigators, on account of the ease with which 
the nuclear process can be followed in the filament, have preferred 
to use fixed and stained but unsectioned filaments, but others have 
resorted to sectioned material as the best means for seeing the 
finer details of the nuclear phenomena. 
In Spirogyra, as is well known, the nucleus contains one or more 
nucleoli that are proportionally exceedingly large. On account 
of the great mass of nucleolar material, it has been generally 
accepted that the network outside the nucleoli either was very 
poor in chromatin or was entirely free from it, the entire chromatic 
material being concentrated in the central bodies which have been 
termed the chromatin nucleoli. A dispute has centered around 
the origin of the chromosomes; whether they came from the reticu- 
lum around the nucleolus or from the nucleolus itself. From the 
time when STRASBURGER (37) first investigated divisions in Spiro- 
gyra to the latest paper by KarsTEN (25) on divisions in the young 
plant as it comes out of the zygospore, the opinions of the investi- 
gators as to the origin of the chromosomes have been divided. 
Altogether over twenty papers have appeared on the subject, 
making the nuclear divisions of Spirogyra the most thoroughly 
studied of those of any algal form. 
In STRASBURGER’S original contribution, which appeared in 
Zellbildung und Zelltheilung (1875), he claimed that the nucleolus 
or nucleoli by first falling into granules, which arrange themselves 
at the middle of the spindle, form the plate. This view he modi- 
fied in 1882 (3'7) when he returned again to the study of Spirogyra, 
then arriving at the conclusion that in the species he was studying 
(S. majuscula) there was a nuclear cavity, the ends of the chromatin 
loops being at the poles of the spindle. This structure forms the 
equatorial plate, the nucleolus in the meantime having disappeared 
