JNTROD UCTION. § 



8. Growth of the cell-wall. — As the cells become older 

 the wall may increase in thickness. It must also increase in 

 area as the cells grow in size. The growth in area is usually 

 accomplished by putting new particles between the older 

 ones. Growth in thickness is rarely uniform. Pits or pores 

 are formed in the wall when it thickens except at these spots. 

 When the thin parts are large and only certain spots or lines 

 grow thicker, the wall shows projecting spikes, bands, or 

 threads. 



