Characteristics of thrombus growth differ with mouse genotype. Times after FeCl₃-induced injury are indicated (min). In wild-type mice (WT), numerous adherent fluorescently labeled platelets can be seen 4 minutes after FeCl₃ treatment. Thrombi usually grow fast and cause vessels to occlude at the site of injury (15 minutes). In vWF^–/– mice, very few platelet–vessel wall interactions were seen at the early time points, but thrombus formation occurred (13 minutes). Thrombi usually stopped growing at the later times, leaving a small channel open (arrowheads, 29 minutes) with high shear flow. The dark thrombus at this time point indicates that few new platelets were recruited, and platelet fluorescence was bleached after a long exposure to UV light. In Fg^–/– mice, early platelet depositions were similar to wild-type mice (4 minutes), and thrombi grew very efficiently (bright thrombi). However, thrombi were not stable. They were often stripped off the vessel wall by blood flow (two sequential panels at 17 minutes) and ultimately led to a downstream occlusion (20 minutes with fluorescent platelets suspended in stagnant blood). The arrow in this panel (Fg^–/–, 20 minutes) shows a thrombus formed in a neighboring venule. In the double-knockout mice (vWF/Fg^–/–), very few fluorescently labeled platelets were seen on the vessel wall at an early time point (4 minutes), but delayed thrombus formation occurred with frequent embolization (two sequential panels at 27 minutes). The majority of the double-deficient arterioles eventually occluded.