26 



Growth 



side view, as in the dividing cambium cells figured by Bailey (1920«), 

 the phragmoplast appears in section as two spindles at the edge of the 

 developing cell plate. In face view it looks like a cytoplasmic "halo." The 

 phragmosome and the phragmoplast, and the function of each in cell 

 division, have sometimes been confused. The difference is made clear by 

 Esau ( 1953£>, her Fig. 3-10 ) . In some dividing vacuolate cells, such as 

 those of the cambium, the phragmosome is either absent or has not 

 been observed. 



Fig. 3-2. Phragmosomes in various cells, a-c, normal tissue; c, in face view showing 

 anastomosing strands; d, e, mature cells near wound face beginning to divide. (From 

 Sinnott and Bloch. ) 



The significance of the cytoplasm in cell division has been emphasized 

 by Muhldorf ( 1951 ) . The general problems of cell division in plants are 

 treated at length in Tischler's monumental book ( 1951 ) . 



The factors that determine whether a cell will divide or not are various 

 and have been much discussed. The size of the cell itself is evidently 

 one of these factors. In actively meristematic regions, the dividing cells 

 are usually of about the same size. This means that each daughter cell, 

 after division, enlarges until it reaches the size at which its mother cell 

 divided, and then itself divides. After division ceases, the cells usually 

 expand considerably. 



Size in dividing cells is by no means always constant, however. Wagner 



