Eight weeks after anthesis (post-anthesis), fruit (approxi- mately 10 mm 18 mm in size) was collected from the four cultivars of citrus species mentioned above. The fruit was surface disinfected by soaking for 15 min in a 10% sodium hypochlorite solution containing 0.1% wetting agent (Tween 20); the ovules were extracted with the aid of a dissecting microscope (Fig. 1a and b) and placed on a modified Murashige and Tucker (MT) (1969) medium containing 500 mg/L malt extract (ME) with 5% (w/v) sucrose and 1% (w/v) Difco bacto agar, pH 5.7. The content of the medium used was exactly according to Kochba and Spiegel-Roy (1973). Adenine (40 mg/L) was added to the MT + ME medium for induction of nucellar callus from the ovules of Washington Navel orange and Clementine mandarin. For lemon varieties only, embryo- genic calli was stimulated from the base of very young embryos in the presence of 2.26 mM 2,4-D in solidified MT medium supplemented with 5% sucrose (Fig. 1c). Culture conditions have been reported before by Vardi et al. (1982). Ovular calli have been sub-cultured on solidified MT medium containing 5% sucrose for the stabilization of callus for a year (Fig. 1d).