Abstract: A new stain-clearing procedure has been developed for embryological observations on whole mounted specimens. Ovules of Helianthus annus and Nicotiana tabacum as well as ovaries of Oryza sativa were stained with diluted Ehrlich's hematoxylin for a proper short time, followed by steps of washing and dehydration, and finally cleared and mounted in methyl salicylate. When observed by ordinary bright-field microscopy, the embryo sacs before fertilization and the embryos and endosperms after fertilization were clearly visible. The gynogenic embryoids induced in unpollinated rice ovaries in vitro were also finely detectable. The Ehrlich's hematoxylin-methyl salicylate technique has the merits of rapidity in specimen preparation, high contrast and three dimensional view, needlessness of phase- or interference-contrast equipment, and the feasibility for a wide range of materials. The special significance of this technique for in vitro embryological studies is emphasized.

Key words: Clearing technique (ovule, ovary), Embryo sac, Embryo, Endosperm, Embryoid