BOTANY 



fertilised egg is known to all of us. The process 

 of cell-division is not, however, a simple cutting 

 in two, as in the multiplication of bacteria, but a 

 remarkably complex phenomenon in which the 

 nucleus plays the chief role. Its contents during 

 the period of mitotic division become separated 

 into a group of bodies known as chromosomes, 

 whose number and relative size and shape are con- 

 stant for the nuclei of any species, as is also to some 

 extent their arrangement in the nucleus. These 

 bodies represent the only parts of the nucleus which 

 are passed on as structural entities from cell to cell. 

 There are many reasons for believing, many lines 

 of experimental evidence which indicate, that they 

 are chiefly concerned in the determination of 

 hereditary differences ; and that the stability of 

 the species and the regularity of its developmental 

 stages are controlled in large measure by the presence 

 in every cell of a nucleus, in which these structural 

 relationships of parts are maintained from one cell- 

 generation to another. In the process of mitotic 

 nuclear division the essential feature is the splitting 

 of the chromosomes lengthwise, so that the daughter 

 nuclei get exactly equal shares of every part. The 

 meticulous accuracy with which this process is carried 

 through shows that it is of fundamental importance 

 in the development and life of the organism. 



Another point to which reference must be made 

 is this. There is one unique division in the life- 



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