THE PLANT CELL 



161 



J 



out of the vacuole (osmotically) and the bounding layer of proto- 

 plasm shrinks away from the wall (Figs. 168, 7?; 169,1?). The 

 force that keeps the layer of protoplasm against the cell wall is 

 called cell turgor. 



The mass of protoplasm inclosed by the cell wall is called 

 the protoplast, and always contains at least one nucleus. Some 

 plant cells have many 

 nuclei. The posi- 

 tion of the nucleus 

 is somewhat variable. 

 In the cell of the pond 

 scum (Fig. 168, A, a) 

 it is situated in the 

 middle region and 

 held in place by deli- 

 cate strands of proto- 

 plasm which run out 

 to the protoplasmic 

 layer under the cell 

 wall, but the nucleus 

 frequently lies just 



under the wall, as in FIG. 169. Cell structure of the moss leaf 



(Funaria) 



, two living cells from a leaf, showing the numer- 

 ous chloroplasts and the position of the nucleus 

 n in the layer of protoplasm under the cell wall ; 



B, living cell after treatment with a salt solution, 

 the protoplast contracted away from the cell wall ; 



C, stages illustrating the division of the plastids, 

 starch grains shown in their interiors 



the moss leaf (Fig. 



matophores are gen- 

 erally found in the 

 outer layer of proto- 

 plasm under the cell 

 wall. There are also many granules in the protoplasm, some of 

 them minute globules of oils and fats and others of a proteid 

 character. Many of these are food products in the cell. Finally, 

 the central portion of the cell generally contains a single vacuole 

 filled with cell sap. 



It is clear that the protoplast of the plant cell corresponds to 

 the entire Amozbq, or any other animal cell. The cell wall is a 



