11 



cavities being filled with nuclear sap or nutrient material 

 (Fig. 2-3). Biitschli* considered this net-like appearance 

 to be due to the section of minute globules — alveoli — of 

 protoplasm enclosed in another substance of different 

 consistency, as in an emulsion, and which formed the walls 

 of the net. Both of these and other forms have been 

 described. 



THE CHROMATIN 



is so named because of its strong affinity for taking up 

 stains, haematoxylin and certain basic stains as methyl 

 green, safranin, &c. It occurs in the form of minute 

 granular bands lying across linin threads (Fig. 5), and both 

 constitute in the nucleus the fine more or less deeply- 

 staining reticulum, the movements of which are such 

 prominent features in the early stages of the complex 

 processes of mitotic or indirect nuclear division. Durmg 

 these changes it becomes deposited at different points m 

 much larger masses, karyosomes or net-knots, eventually 

 it is located in the chromosomes, and sometimes appears to 

 be homogeneous. 



THE NUCLEOLUS. 

 Enclosed within vacuolar spaces of the nucleus are one 

 or more rounded bodies with a dense central part 

 surrounded by a hyaline ring and bounded by a wall of 

 nuclear substance— these are the nucleoli (Fig. 5). In 

 active young cells they are comparatively large, taking up 

 a great portion of the nucleus. They undergo dissolution, 

 partial or complete, during the first stages of nuclear 

 division; others appear during the later phases, and 

 become the nucleoli of the daughter nuclei (Fig. i;)- 



In certain stages of development in pollen mother- 

 cells and embryo-sac mother-cells, a single, very large 



