62 



PLANT CELLS 



There is no general agreement among cytologists regarding the exact 

 classification of the parts of plant cells. The vacuole, for example, is fre- 

 quently classified as a part of the protoplasm because it first appears as minute 

 droplets in the protoplasm of very young cells. Physiologically, however, the 

 vacuole of the mature cell is as distinct an entity as the protoplasm or cell 

 wall and it is therefore considered as a separate part of the cell in this book. 

 The following classification includes the principal parts of a mature plant 

 cell. A few of these parts, as for example the various kinds of plastids, do 

 not occur in every cell. 



The Mature 

 Plant Cell.. 



Cell Wall. 



Middle lamella 

 Primary Wall 

 Secondary Wall 



Cytoplasm, 



Protoplasm 



Plasmodesms 

 Cytoplasmic membranes 

 Undifferentiated cytoplasm 



Plastids 



leucoplasts 

 chloroplasts 

 chromoplasts 

 .elaioplasts 



• Nucleus. 



.Chondriosomes 



Nuclear membrane 

 Nuclear sap 

 Reticulum 

 .Nucleolus 



Vacuole. 



Cell Sap 



Crystals 



Water 



Various compounds 

 in solution or in a 

 state of colloidal 

 dispersion 



The Origin and Development of Cells. — As soon as it became clear that 

 all plant and animal tissues were composed of cells the question of the origin 

 of cells naturally arose. This proved to be a difficult problem for the pioneer 



