Murashige and Skoog is a base for plant tissue culture media.The mixture is without plant hormones or agar which should be added as follows:To maintain callus add 5x10-8g/litre 2 4-D (weedkiller) and 8g/litre agar.To maintain apical meristem or for rooting shoot tips add 0.3mg/litre IAA 1mg/litre kinetin and 6g/litre of agar.