SUMMARYSuspension cultures of celery emhryoids were initiated by transferring portions of differentiating callus to liquid medium. Light microscope studies of the cells and embryogenic aggregates in the suspensions suggested that the emhryoids arose from either single cells within the embryogenic aggregates, when the developing emhryoid remained attached to the clump until the globular stage, or from free floating small groups of cells. Both types of development showed the celery emhryoids to he of single eell origin. When the emhryoid suspension was filtered to remove the larger embryoids and the small emhryogenic aggregates and free floating embryoids were mixed with agar and plated, the development of the embryoids depended on the initial inoculum density. At low density further embryoid development was delayed while at the high inoculum density the emhryoids became green and grew rapidly into torpedo embryoids with cotyledon leaves and roots. At this stage they could be transferred to a simple inorganic medium to develop into plantlets. The effect of inoculum density was thought to be due to a conditioning effect of the environment. It is suggested that the differentiating units in the emhryoid suspension could be used in a cell selection procedure.