A chain growth model for heterogeneous secondary reactions is developed for the pyrolysis of large wood particles and the parameters determined by nonlinear optimization. The model takes both the volatile retention time and cracking and repolymerization reactions of the vapours with the decomposing solid as well as autocatalysis into consideration. The extent of the secondary reactions is strongly influenced by the time and the ratio of the autocatalytic (propagation) reaction rate to noncatalytic (initiation) reaction rate. The wood which has a higher value of the autocatalytic/noncatalytic ratio also has a higher exothermic heat of reaction and yields a higher amount of final char residue. This fact confirms that the heterogeneous secondary reactions lead to carbon enrichment of the final residue and are accompanied with an exothermic heat of reaction. The lower activation energies of the initiation and propagation reactions as compared to primary reactions (competitive reaction model consisting of weight loss and char forming reactions) confirm autocatalysis in large particles. The sealed reactor studies of small quantities of fine wood samples show that heterogeneous secondary reactions and not lower heating rates in large particles are the main source of char formed during the thermal decomposition of large wood particles. The model predictions are in agreement with the weight loss and temperature versus time curves over a wide range of particle size and furnace temperatures.

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Three different strains of Agrobacterium rhizogenes, namely A4, LBA 9402 and LBA 9360 were used for infection to induce hairy root formation in W. somnifera. Strain specificity of the bacterium and frequency of transformation events were analysed. Significant differences were observed between the transformation ability of the different strains of Agrobacterium. The best response in terms of transformation ability and growth of the hairy roots was obtained with A. rhizogenes strain A4, followed by LBA 9402, whereas LBA 9360 strain failed to induce a transformation event. The production of withanolides with special reference to withaferin A was studied through HPLC in the A4 induced hairy root lines and their respective media at different growth phases (i.e. 4,lO and 24 weeks). The presence of withaferin A in the media as well as in the hairy roots of 10-week-old cultures highlights the importance of the present study for the commercial prospects of this plant.

Protoplasts isolated enzymatically from seedling roots, hypocotyls and cotyledons of Lotus corniculatus L. produced callus which underwent prolific shoot regeneration. The rapidity and ease of recovering plants from protoplast-derived tissues makes this forage legume an attractive experimental system for genetic manipulation.

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