THE PLANT CELL 



71 



is termed its function, 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 



