Long-term treatment of metatarsal rudiments by FGF causes inhibition of longitudinal growth and disruption of the growth plate in wild-type but not STAT-1−/− rudiments. E15 metatarsals from STAT-1+/+ and STAT-1−/− mice were cultured for 7 days in the presence or absence of 200 ng/ml FGF1. Longitudinal sections of E.15 (a,d) and 7-day cultured metatarsals (b,c,e,f) were stained with a specific antibody against Col X. (a–f) Micrographs have the same magnification. (Insets) A higher power view of the areas boxed in the low power adjacent micrographs, corresponding to the growth plate area.