﻿NUCLEAR DIVISION OF SPIROGYRA 

 n. NUCLEAR DIVISION IN S. B ELLIS 



Mabel L. Merriman 



(with plates xviii-xx) 



In investigating the nuclear division of Spirogyra three modes 

 of procedure were used. Study of whole mounts fixed and stained 

 gives a better idea of disposition of chromatic material, whereas 

 a study of sections gives a better idea of its structure. For esti- 

 mating duration of phases in karyokinesis and relative activity 

 of parts of nucleus and boundaries of nucleus and cytoplasm, it 

 is necessary to study living nuclei. 



Although many species have been worked upon, none has yet 

 been found that presents favorable material for all these methods. 

 If nuclei are large, as in S. crassa, and so adapted for dissection 

 from whole mounts or for sectioning, then in a living cell close 

 winding of the chromatophores prevents a view of the nucleus in 

 karyokinesis. Hence the study of S. crassa (8) was confined 

 to the study of sections and entire nuclei dissected from the threads. 

 In the studies of 5. bellis a correlation was attempted of nuclear 

 division stage by stage as seen in living cells with similar stages 

 fixed the same evening. The nucleus of this species is plainly 

 visible when living, and when stained its density is not so great 

 but that its structures may be seen readily without sectioning. 

 The stains used were safranin and gentian violet; Haidenhain's 

 hematoxylin with iron alum; and anilin blue with eosin. Since 

 gentian violet stains the cell sheath as well as the chromatic 

 material, the last two combinations of stains gave the best results. 



Material in good condition was obtained from three different 

 sources. It is of interest that in these materials from widely 

 separated localities uniform variations existed, yet all can be 

 included under one type, a type differing markedly from that of 

 S. crassa, already published, and from that of 5. dubia and S. 

 ternata now in preparation. In regard to the nuclear division of 

 •S. dubia, the discovery of 5 chromosomes was made, while in S. 



