Plant cell 



8 BOTANY OF CROP PLANTS 



All vacuoles are bordered by a protoplasmic membrane, simi- 

 lar to the ectoplasm. 



Suspended within the cytoplasm are specialized living 

 bodies, the plastids, also numerous granules, which may be 

 of Uving material and insoluble food particles, such as starch 

 or protein. The cytoplasm may hold insoluble crystals of 

 salts, chiefly calcium oxalate. Let us arrange the parts of 

 cell thus far described in outline form as follows: 



Cell wall (non-living) 



Protoplasmic membrane (living) 



Nucleus (living), containing one or more nucleoli 



Protoplast. { [ plastids (living) 



_ , , I granules (living or non-living) 



Cytoplasm. < ^ . . , .°. . ^' 



I crystals (non-livmg) 



[ vacuoles, containing cell sap. 



The Cell Wall. — The cell wall is a product of the proto- 

 plast. When young it is almost pure cellulose. As the 

 cell grows older, its wall may thicken and become denser, 

 and have added to it certain substances such as lignin, su- 

 berin, cutin and pectin which give it different physical 

 and chemical qualities. 



Plastids. — These are speciahzed masses of protoplasm 

 suspended within the cytoplasm. They vary in size and 

 form. There are three sorts of plastids based upon their 

 color: (i) leucoplastids, colorless; (2) chloroplastids, green; 

 and (3) chromoplastids, yellow, orange or red. 



Nucleus. — ^All typical cells have a definite nucleus. It 

 is wrong to regard the nucleus as the "seat of life" of the 

 cell, for other portions of the cell are all-important, but it is a 

 most essential part of the cell. If the nucleus is separated 

 from the cytoplasm by artificial means, the cell dies. Its 

 presence is needed, it seems, to stimulate respiratory activity. 

 Moreover, reproduction of the cell — ^its division to form two 



