April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 383 



Minute Structure of Nuclei and Nucleoll 



Let us next study the minute structure of nuclei and 

 nucleoli, by beginning with fig. 45, which shows two nuclei 

 of Scilla just commencing to conjugate. 



Both nuclei are surrounded by a comparatively thick 

 unstained nuclear membrane {n. m.), having a refractive 

 index almost the same as that of turpentine-balsam. This 

 membrane is traversed by a number of radial pores which 

 are visible, because they contain a substance which has a 

 less-high refractive index than the nuclear membrane. 

 Lining the inner aspect of the membrane are a number 

 of irregularly lenticular-shaped chromatin- elements (chr. 1), 

 which may or may not be in communication with one 

 another by means of fine strands of chromatin, and wliich 

 often are arranged as the beads of a rosary. The difference, 

 in their thickness, as shown in the figure, is only apparent, 

 for the chromatin-plates being arranged in a globular fashion, 

 will not be all in focus at the same time. In addition to 

 these peripheral somata {chr. 1), a number of more or less 

 central ones {chr. 2) are arranged along nuclear threads {n. f.^) 

 which pass from the nuclear to the nucleolar membrane {1). 

 Some of the threads are distinctly tubular, and show a double 

 outline {n. /.), while others are either too minute to be recog- 

 nised as tubes, or perhaps consist of solid strands {n. f.^). 

 Working even with the very best appliances, and taking 

 every precaution, I have found it sometimes impossible to 

 trace a filament along its entire length, and it is just possible 

 that, what I describe as solid strands, corresponds to the anas- 

 tomosing branches connecting the chromosomes with one 

 another. 



Surrounding the nucleolus is a nucleolar membrane (i), 

 fainter, and of a higher refractive index than the nuclear 

 membrane. Similarly as in the nuclear membrane, a number 

 of very minute dark radially-placed pores or stride can be 

 observed, and on careful focussing it is possible to see that 

 these strise are continued into very delicate cilia-like fibrils 

 (5) radiating out from the nucleolar membrane into the 

 nuclear hyaloplasm {n. h.). The fibrils are not stained by 

 haematoxylin, and are only visible because of their refractive 

 index being lower than that of the nucleo-hyaloplasm. 



