[Chap. XXXVII HEREDITY IN PLANTS 447 



consider certain irregularities that are known to occur, and also the way 

 in which they influence the development of plants. 



Cell division in vegetative cells: mitosis. In Fig. 207 certain stages in 

 the behavior of chromosomes in each cell division that occurs in all 

 growing regions of plants are depicted. It should be easy to visualize the 

 continuous behavior of chromosomes between the stages depicted. The 



Fig. 208. Cell division and enlargement in a root tip of onion. A series of stages 

 in the behavior of chromosomes during vegetative cell division is represented 

 and labeled a to g. Courtesy of World Book Co. 



whole process may be completed within tliirty minutes or it may extend 

 over a period of several hours. Cells in various stages of division may be 

 seen in microscopic sections cut from some growing region of the plant 

 ( Fig. 208 ) . Many facts about vegetative cell division ( "somatic mitosis" ) 

 are known; but for the present purpose of seeing the relation of chromo- 

 some behavior to the transmission of hereditary factors, it is necessary 

 only to study the diagrams carefully. Then it will be seen that every 

 time vegetative cells divide, each chromosome of a cell splits ( divides ) 



