الفهرس 
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Abstract
This study was carried out in the experimental farm of Sakha Horticulture Research Station, Kafr El- Sheikh Governorate during two successive seasons (2014 and 2015). This study included two experiments in each season. The first experiment aiming to study the effect of the pinching and foliar spray of paclobutrazol (PBZ) on the growth, flowering and chemical composition of Zinnia elegans, Jacq. and Celosia argentea, L. var. Plumosa plants. After one week from transplanting, the plants were divided into two groups, in the first group the apical buds were removed (pinched) while in the second group they were without pinching (non- pinched). Both groups were twice sprayed with PBZ at four concentrations (0, 50, 100 and 150 ppm) at 3 and 21 days after pinching. The second experiment aiming to study the effect of foliar spray of silicon dioxide and ascorbic acid at four concentrations (0, 100, 200 and 300 ppm) for them, on the growth, flowering and chemical constituents of Catharanthus roseus, (L.) G. Don. Foliar spray was carried out three times at three weeks interval, starting from one week after transplanting. All plants in both two experiments were fertilized with 4 g/plant calcium super phosphate (15.5% P2O5) in one dose at the soil preparation before transplanting, 8 g/plant ammonium sulphate (20.5% N) and 4 g/plant potassium sulphate (48.5% K2O), nitrogen and potassium fertilizer were divided into two equal doses. The first dose was added after three weeks from transplanting and the second one was added four weeks later. The results showed that the pinching treatment increased stem diameter, number of branches/plant and fresh and dry weight of vegetative parts/plants for both plants, compared to the unpinched plants. Spray of paclobutrazol generally reduced most vegetative growth and flowering parameters (plant height, leaf area, fresh and dry weight of vegetative parts/plant, flower diameter as well as fresh and dry weight of flowers/plant). Furthermore, spray of paclobutrazol at high rate (150 ppm) had the most pronounced effect on growth of Zinnia elegans, Jacq. and Celosia argentea, L. in the majority of parameters. The application of silicon significantly increased stem diameter, number of branches/plant as well as fresh and dry weight of vegetative parts/plant compared to control. The high levels (200 and 300 ppm) gave the greatest values for these parameters. Spray of ascorbic acid significantly increased plant height, stem diameter, leaf area, fresh and dry weight of vegetative parts and flowers/plant, number of flowers/plant and flower diameter when compared to control.