NUCLEAR DIVISION 



21 



The intercalary meristems found at the base of the internode 

 in Grasses, and at the top of the internode in Labiatc'e, 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 ahvaj'S takes the 

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

 separated from one another by the development of an intervening 



Fig. io. — 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 ; ti , nucleolus. 



wall. Thus two new cells are established, each with its own 

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

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

 phenomenon 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 



