Only one cotyledon attached to the shoot apex is sufficient to ensure continued growth without adding nutrients to the medium. Perhaps some indication of the extent to which development of the explants is dependent on the presence of apex, hypocotyl or cotyledons. Compare material isolated from different species. Remove one or both cotyledons and compare growth with that of complete explants. Try growing isolated cotyledons only.
Explant response is enhanced by the addition of nutrients to the agar.
Ready-prepared mixes, e.g. Murashige and Skoog, are available from Philip Harris, Sigma etc. Ask for 'MS salts - without added sugar' . The plasticity of explants grown on a range of media throws light on plant development and plant repair mechanisms. The work on the protocol described here was carried out with the help of Dr David Hanke of the Dept. of Plant Sciences, University of Cambridge. This material is copyright protected.