THE PLANT CELL 85 



cellular structures of the three zones in the embryo. 

 They are characterized by thin walls and the possession 

 of protoplasmic contents. Typical prosenchyma cells 

 are formed in the plerom region of the embryo. They 

 differ from parenchyma in the possession of thick 

 walls, and the protoplasmic contents are inconspicuous 

 or lacking. These distinctions are not absolute, and 

 the form or shape of the cell may be used as a basis 

 for further classification in doubtful instances. Pro- 

 senchymatic elements are usually in the form of long 

 fiber cells with sharp-pointed ends, whereas parenchy- 

 matic cells are usually spherical or isodiametric in 

 shape and do not possess pointed ends. 



