THE PLANT CELL 



71 



is termed its functionj and the existence of a multi- 

 cellular organism is dependent upon the proper func- 

 tioning of its component tissues. 



Cytology, or the study of cells, reveals many struc- 

 tures within each cell, and it is customary to consider 

 a cell as consisting of a cell -wall and the protoplasm, 

 or material within this wall. The study of cell walls 



Plate 28. — Plant Cell from Tradescantia Stem. 



1. Cell wall. 2. Nucleus. 3. Vacuoles. 4. Cytoplasm. 5. Nucleolus. 

 6. Nuclear membrane. 7. Nucleolar membrane. 



and their modifications is a subject of great impor- 

 tance in that part of vegetable histology dealing with 

 the microanalysis of foods and drugs. The proto- 

 plasm is a semi-solid substance in which the presence 

 of several structures, or cell contents, can be demon- 

 strated by proper treatment (Plate 28). These struc- 

 tures may be classified as protoplasmic contents, or 



