422 VEGETABLE PHYSIOLOGY 



respects. This is known as gemmation or budding. It may 

 go on so rapidly that the new cell in turn may put out a 

 bud of its own before it is cut off from its parent, and in 

 that way chains of cells may be produced (fig. 162). 



A more general method of the division of the cell is 

 of a highly complicated character, and is preceded by 

 an elaborate division of its nucleus. This structure we 

 have seen consists essentially of a delicate network of 

 fibrils of chromatin embedded in a hyaline substance, the 

 whole being surrounded by a more or less well-defined out- 

 line derived from the cell-protoplasm, and known as the 

 nuclear membrane. Associated with it in some cases are 



G ^ o 



*> 



abed 

 Fio 162. SACCHAROMYCES CEREVISI^E, OR YEAST-PLANT, AS DEVELOPED 



DURING THE PROCESS OP FERMENTATION. X 300. 



a, b, c, d, successive stages of cell-multiplication. 



two small centrospheres. The process of division, which is 

 known as Karyokinesis, or Mitosis, begins by the network 

 of fibrils becoming coarser and gradually separating to 

 form a long coiled fibre. The nucleoli disappear and the 

 nuclear membrane ceases to be distinguishable. At the 

 same time, in those cases in which centrospheres have 

 been seen, they shift their position and come to lie on opposite 

 sides of the nucleus at some little distance from it. The 

 long coiled fibre of chromatin breaks up into a number of 

 pieces, often V-shaped, which point towards the centre of 

 the nucleus. The number of these varies in different cases, 

 but is constant in the successive divisions of an individual. 

 These pieces of the fibre are known as chromosomes. The 

 chromatin in them is broken up into small portions which 

 are separated from each other by smaller films of unstain- 

 able substance. 



