The continued requirement for inducer for the development of macrophage and granulocyte colonies

Rat bone marrow cells were seeded as mass cultures or for cloning together with inducer required for colony formation, and at various times after seeding, the cells were re-seeded for cloning either with or without inducer. The results indicate that the development of both macrophage (M) and granulocyte (G) colonies requires a continued supply of the inducer. No M or G colonies were produced when the inducer was replaced by erythropoietin.