NUCLEAR DIVISION IN-SPIROGYRA CRASSA 
M. L. MERRIMAN 
(WITH PLATES XI AND XII) 
Although the cytology of Spirogyra has been investigated 
probably more than that of any other alga, it still offers a fruitful 
field of inquiry. The varying accounts, beginning with Srras- 
BURGER’S paper in 1882 as to the chromatic or non-chromatic nature 
of the parts of the nucleus and the réle they play in karyokinesis, 
have left many questions open. 
S. crassa was chosen for this investigation on account of the 
large size of the nuclei, spindles of which can be detected with a 
magnifying glass. Specimens were fixed in weaker chromacetic, 
Flemming, and Bouin mixtures. Sections were cut 3-5 # in thick- 
ness. When spindles of the metaphase were sectioned, 3-5 sections 
of one spindle were obtained. The stains used were safranin and 
gentian violet, Heidenhains hematoxylin with iron alum. Extended 
observations upon other species with smaller nuclei, but more easily 
studied in the living cells because of their greater transparency, have 
aided in making the interpretations given in this paper. In order 
to interpret sections of the large nuclei of S. crassa more satisfactor- 
ily, nuclei in different stages of division were also dissected from the 
filaments and from them whole mounts made. This dissection was 
necessary as nuclei in S. crassa are surrounded by a substance 
ramifying in the cell and so rendering them somewhat opaque. 
This condition, as well as that of their being obscured by the close 
Winding of the chromatophores, prevented the adequate study of 
their division in the living cells. 
In the living cells and in the mounted specimens three mem- 
branes can be distinguished clearly, one surrounding a central 
dense spherical body, a second surrounding a less dense larger body 
containing the first, and lastly a third which is continuous with the 
Suspensors which in turn are continuous with the cord on which 
Boubier (3) has demonstrated the pyrenoids are dependent. These 
319] [Botanical Gazette, vol. 56 

