NUCLEAR DIVISION 



21 



The intercalary meristems found at the base of the internode 

 in Grasses, and at the top of the internode in Labiatae, consist 

 of a transverse plate of small meristematic cells in which no 

 definite regions can be distinguished. 



In the process of cell-division the nucleus always takes the 

 lead, dividing into two parts, or daughter-nuclei, which become 

 separated from one another by the development of an intervening 





A 



: *?m 



'IG. 10. Early phases of mitosis (after Fraser and Snell). A, resting 

 nucleus ; B, spireme ; C, formation of chromosomes ; D, establish- 

 ment of nuclear spindle, ch., chromosomes ; n, nucleolus. 



Thus two new cells are established, each with its own 

 mcleus similar in all respects to that of the cell from which they 

 >riginated. Amongst some of the lower plants, and as a rare 

 )henomenon in the higher, the nucleus merely divides into two 

 portions by a median constriction. This is spoken of as direct 

 nuclear division (amitosis). 



More usually, however, there is a sequence of complex changes 

 in the nucleus preparatory to and during division, and this whole 



