To study the effect of EDTA on cell wall structure and the reversal of this effect by uranyl ion, thin sections of pea root tips were examined in the electron microscope. EDTA is known to facilitate separation of the cells in root tips. When sections of fixed and embedded EDTA-treated roots are floated on a uranyl-acetate solution, a loose network is revealed that would seem to be cellulose. Incorporation of uranyl into the roots, if it occurs prior to fixation, brings about recementation of the cells. After such treatment, a marginal darker area and a median brighter one can be observed in the wall, and the whole structure appears more compact again. Comparison of the results of the various treatments suggests that cellulose-cementing material is dispersed throughout the entire wall, and that its distribution parallels that of cellulose.

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