Divergence angles of branching tubules are governed not by sequence but by the presence of other tips. Normal kidneys cultured intact (a) show a wide angle of first branching (`1'), and narrower second (`2') and subsequent branches. Real angles from this specimen are indicated on the figure and mean values can be seen in the green bars of Figure 1d. An unbranched ureteric tip cultured with its own mesenchyme (b) shows a similar wide-then-narrower pattern. An already-branched tip (c), which would naturally go on to produce a narrow branch angle, begins by producing a wide angle characteristic of the first branch when it is cultured alone (with its own mesenchyme). In the images, the area behind the red dotted line, labelled `retro', is a branching system that develops from the bladder end of the cut ureteric bud, behaviour that has already been described : data were not gathered from the `retro' branching system because its first branch occurred later then the normal ones, with very variable timing. (d) Shows branching angles quantitatively, a,b, and c referring to the culture methods shown in (a), (b) and (c) and colours in the graph matching the colour bars under each micrograph: error bars represent standard error of the mean. In all cases, second branch angles differ from first branch angles with p <0.05 (p values are given in the main text).