الفهرس 
Introduction
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Abstract
This investigation was carried out at El- Gemmeiza Agricultural Research Station, Gharbia Governorate, during 2006/ 2007 and 2007/ 2008. The objectives of this investigation aimed to evaluate performance of flax varieties under different sowing and harvesting dates and its effect on straw, seed and fiber yields and its components as well as quality. Three separate experiments every season in split-plot design with three replication was used. The three harvesting dates were randomly arranged in main plots and the four studied varieties were allocated in sub-blots. • The main finding could be summarized as follows: 1- Sowing dates effects : The results showed that early sowing on 20th October, gave tallest plants and highest in, technical length, fiber length, fiber fineness, fiber yield/ faddan, and significantly increased straw yield/ plant, straw yield/ faddan and fiber yield/ plant. The results indicated that sowing flax on 10th November significantly increased seed yield/ faddan, straw yield/ plant, straw yield/ faddan and fiber yield/ plant. Sowing flax on 1st December significantly decreased all the studied characters but increased stem diameter in the second season. 2- Harvesting dates effects: The results showed that early harvesting after 135 days from sowing significantly increased only main stem diameter in both seasons. Delaying harvesting to 150 days from sowing significantly increased straw yield/ plant, fiber yield/ plant and fiber yield/ faddan in both seasons. Delaying harvesting date to 165 days from sowing significantly increased plant height, technical length, fiber length and fiber fineness, seed yield/ plant, seed yield/ faddan and straw yield/ faddan in both seasons. 3 –Varietal performance : The results indicated that Sakha 2 and Giza 8 surpassed other studied varieties in number of capsule/ plant, seed yield/ plant, seed yield/ faddan, seed index and straw yield faddan in both seasons. Sakha 3 and Sakha 4 significantly exceeded other studied varieties in plant height, technical length, fiber length, fiber yield/ plant, fiber yield/ faddan, fiber finesses and number of seeds/ capsules in both seasons. Conclusion It could be concluded that for maximizing fiber yield of flax per unit area sowing Sakha 3 or Sakha 4 varieties maybe sown on 20th October and harvested after 150 days from sowing. In addition, for maximizing seed yield per of unit area Giza 8 or Sakha 2 varieties maybe on 10th November and harvested after 165 days from sowing under the environmental conditions of Gahrbia district.