GROWTH 



285 



that in the lower part of the growing region the meristematic cells 

 pass into the second stage of growth. This is termed "elonga- 

 tion." This stage is characterized by the appearance of vacuoles 

 in the protoplasm, which become filled with a watery content, 

 the cell sap. These vacuoles enlarge rapidly, and finally nothing 

 is left of the protoplasm but a thin lining appressed to the 

 walls. The whole cavity of the cell constitutes now a large 



Fig. 110. — Successive stages in the growth of root cells (after Brown). 



central vacuole. The volume of the cell naturally has increased, 

 the walls having grown considerably, but the amount of protoplasm 

 apparently remains unaltered (Fig. 110). 



The enlargement of the cell during the stage of elongation 

 results from different causes than those operating during meris- 

 tematic growth. There we had to deal with an increase in the 

 amount of protoplasm ; and here with an increase in the quantity 



