الفهرس 
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Abstract
The Thesis overall goal was to examine the effect of Cd and Zn on root hair development and nodulation. Our specific goals were to examine the1.Effects of heavy metals on the early stages of symbiosis between white clover and Rhizobium leguminosarum bv. trifolii. 2- Toxicity of heavy metals to R.leguminosarum bv. trifolii and nitrogen fixation. 3- Soil pH and heavy metal effects on the early stages of R. leguminosarum bv. trifolii and white clover symbiosis and nitrogen fixation . 4- Tolerance of R. leguminosarum bv. trifolii to increasing Zn2+ and Cd2+ activities in solution culture .