الفهرس 
Introduction
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Abstract
Monacha cartusiana is one of the most commonly distributed land snails in Egypt that infects the majority of field crops. The work described in this thesis has been undertaken with the aim of searching naturally occurring substances with molluscicidal activity. The extracts of eleven selected plant species were tested against Monacha cartusiana and only four were considered toxic. These are Cyperus articulatus L. (Cyperaceae), Ottelia alismoides (L.) Pers. (Hydrocharitaceae), Erythrina ulei Harms (Fabaceae) and Balanites aegyptiaca (L.) Delile (Balanitaceae). Various chromatographic and spectroscopic methods were used. Processing of Cyperus articulatus revealed the isolation and structure elucidation of thirty seven compounds, which could be classified into eight monoterpenoids 1-8, twenty three sesquiterpenoids 9-31 and six fatty acids 32-37. Processing of Ottelia alismoides resulted in the isolation and structure-elucidation of a known compound, 1S,3S,3aS,7aS-ottelione 38, and seven new diphenyl heptanoids (curcuminoids) 39-45. This is the first report of curcuminoids from the family Hydrocharitaceae. Separation of the extract of Erythrina ulei gave four alkaloids 46-49, which were reported previously from other Erythrina species. from the oil of Balanites aegyptiaca fourteen fat derivatives 50-63 were identified and from the glycosidic fraction, after acid hydrolysis, the aglycones diosgenin 64, yamogenin 65 and 3,5-spirostadiene 66 were identified. Our study revealed that the following generalizations concerning structure-activity relationship could be concluded: Some sesquiterpene lactones, especially germacranolides, are active. The presence of α,-unsaturated ketonic function stimulates the activity. The presence of the Nitrogen atom in the lactones gives more probable activity. Steroidal saponins, not triterpenoidal, are active.