NUCLEAR DIVISION IN ZYGNEMA. 
MABEL L, MERRIMAN. 
(WITH PLATES III AND Iv) 
THE species of Zygnema chosen for this investigation possesses 
a nucleus unobscured by chromatophores, and hence one in which 
division stages can be easily followed. No zygospores were found 
in the material, so the species could not be identified with any degree 
of accuracy. The number of pyrenoids are normally two, one on 
each side of the nucleus. The material was gathered from the same 
locality, the margin of a brook, during the months of August and 
September of two successive years. The filaments were studied in 
a living condition to make sure of the presence of dividing nuclei, 
and were then killed in chromacetic acid and the weaker solution of 
Flemming for later study. The greater part of them were killed in 
the evening, as it was also desired to secure division stages of other 
Conjugatae, which grew in great abundance in the locality and have 
been reported by investigators as dividing more actively at night. 
Of these, three species of Spirogyra and two of Mesocarpus will 
furnish the material for a later contribution. 
As nearly all the literature upon the cytology of the Conjugatae 
relates to forms of Spirogyra, its consideration will be deferred until 
the completion of further studies in the nuclear division of the group. 
It is hoped then to bring into accord all the observations as to the 
character of chromatin and nucleoli. 
Filaments of Zygnema treated with the combination stain of 
safranin and gentian violet, were found upon examination to have 
retained the violet only in the cell sheath, while the nuclear structures 
and pyrenoids retained the safranin. Various results were obtained 
with those treated with Heidenhain’s haematoxylin in combination 
with iron alum and eosin. As the same length of exposure to the 
stain did not suffice for Spirogyra and Mesocarpus growing entangled 
with the Zygnema, the material was allowed to remain in the staining 
fluids for a shorter or longer time. Filaments show pyrenoids stained 
black by the haematoxylin, the nuclear structures retaining the 
eosin; or the pyrenoids may be stained red by the eosin, and the 
43] [Botanical Gazette, vol. 4x 
