الفهرس 
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Abstract
The crucial histological differences between various incompatible Host-parasite interaction systems have been investigated, in particular hypersensitivity in French bean and avirulent races of Colletotrichum lindemuthianum. The hypersensitive responses of bean cells was studied following inoculation of hypocotyls with each of the non-pathogenic fungi, botrytis cinerea, Cladosporium cucumerinum, Fusarium solani f. sp. batatas and Colletotrichurn lagenarium. Hypersensitivity and other forms of resistance and susceptibility mwas also studied in bean roots inoculated with C. lindemuthianum (pathogen) mand C. lage.narium (non—pathogen). Certain biochemical changes in inoculated resistant and susceptible mcultivars were investigated; phaseollin and a number of other phytoalexins yere found in the roots. Stress induced hypersensitivity was achieved by keeping bean hypocotyls at suitable temperature during the early, critical, stages of the interactions. The cytology of C. lindemuthianum infection in French bean as reported by Mercer (1971), has been reinvestigated and clarified including changes in ultrastructure in cells adjacent to those responding directly to infection, and degradation and penetration of cell walls. Changes in ultrastructure of infected hypocotyls following transfer from 18°C to 25°C were also studied as were cell structures which seemed to be involved in limiting the enlargement of the lesion and spread of the pathogen at successive stages in infection and colonization.