This thesis consists of four chapters. The first chapter gives a general introduction dealing with the nature of secondary metabolites and the skeletal types found in the Hepaticae (liverworts). This is followed by a discussion of the chemical constituents found in Plagiochila spinulosa (Chapter Two). Six dihydrophenanthrene derivatives, a pentasubstituted benzene, a fusicoccane derivative and three bibenzyl-diterpenoid conjugate compounds were isolated. Among these compounds one dihydrophenanthrene and one bibenzyl-diterpenoid are new and a fusicoccane derivative is isolated for the first time from this species. The structures of these compounds were determined mainly using 1H and 13C NMR spectroscopy. Definitive evidence for the structures of the dihydrophenanthrenes was obtained from NOE difference experiments. The structure of the pentasubstituted benzene derivative was established by a long-range deltaC/deltaH correlation experiment. Chapter three deals with the chemical constituents of Barbilophozia barbata. The sesquiterpenoid hydrocarbon,gymnomitrene, two acorane derivatives, (1S*,10S*)-2R*,3S*-diacetoxy-4,7(11)-acoradien-8-one and (1S*,10S*)-2S*-acetoxy-4,7(11)-acoradien-8-one and a dolabellane diterpenoid, 18-acetoxy-3S,4S;7S,8S-diepoxydolabellane were isolated. The acorane monoacetate is a new compound. The secondary metabolites of Frullania tamarisci form the subject matter of the final Chapter. Six eudesmanolides, frullanolide, alpha-cyclocostunolide, beta-cyclocostunolide, gamma-cyclocostunolide, oxyfrullanolide, 5beta-hydroxy-4(15)-eudesmadien-6,12-olide, a germacranolide, costunolide and one pacifigorgiane derivative, tamariscol were isolated. Oxyfrullanolide and beta-cyclocostunolide are reported for the first time in this species. New compound 5beta-hydroxy-4(15)- eudesmadien-6,12-olide was isolated as a mixture with, its 5-epimer, oxyfrullanolide.
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