THE LIVING PLANT 



19 



- Ce// Wa// 



Nuc/eus 



Ce//Sap-- If- 



Sands of 

 Cytop/as/r, 



reproduction. One of the common ways in which it aids 

 reproduction is through division, whereby two cells are 

 developed from the original one. 



33. Cytoplasm (Fig. 3) is the name given to all the 

 protoplasm within the 



cell-wall, with the ex- 

 ception of the nucleus. 

 Together with the nu- 

 cleus, it carries on the 

 activities of the cell. 

 It contains vacuoles, 

 granules, plastids, and 

 crystals. 



34. Vacuoles. In 

 the cytoplasm occur 

 what frequently ap- 

 pear in young growing 

 cells to be small glob- 

 ules of clear liquid. 

 These are called vac- 

 uoles and the liquid 

 is known as cell-sap. 



As the cell becomes older, the vacuoles become larger until 

 frequently a single vacuole may occupy most of the cell. 

 In the cell-sap are acids and salts which cause the vacuoles 

 to take up and hold a quantity of water, enabling the proto- 

 plasm to fill the entire cell and to exert pressure against 

 the cell- wall. This pressure is called turgor. Turgor is 

 necessary for the enlargement of the growing cell and gives 

 strength to the plant. When turgor is wanting, as in 

 herbaceous plants which have wilted, the soft tissues 

 collapse and the plant loses its rigidity. The vacuoles 

 store manufactured food materials until they are needed 

 by the cell. They contain also excretory products which the 

 protoplasm cannot use. 



FIG. 4. Cell showing circulation of the cytoplasm 

 (streaming). Arrows show direction of move- 

 ments. 



