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Plate I. The ultrastructure of plant cells 



a. Electron micrograph showing the structure of cytoplasm in maize (Zea 

 mays) root cells at a distance of 1-1-5 mm from the root tip. Fixation was 

 with potassium permanganate which accentuates membranes. Invagination 

 of the plasmalemma can be seen, and also some parts of the endoplasmic 

 reticulum. The central vacuole of a mature cell arises by coalescence of 

 smaller vacuoles. Magnification 2,025 x (Photograph reproduced by 

 courtesy of W. G. Whaley and H. J. Moilenhauer). 



Key: N nucleus; Va -vacuole; V = cytoplasmic vesicle (not clearly dis- 

 tinguishable in a); W=cellulose cell wall; PI = plasmalemma; T=tonoplast 

 (not clearly distinguishable in b); Er== endoplasmic reticulum; g= small dense 

 granule (ribonucleoprotein particle). 



