Fig. 5. Analysis of multiply branched laterals argues that growth is distributed all along the proximal distal axis. The micrographs on the left are of a trc⁸/trc¹ pupae. The developmental rate of such mutant pupae is variably delayed. The experiment started at 32 hours after white pre-pupae. The lateral is unbranched in panel A, but a branch is visible in B. A second branch can be seen in C. The graph on the right plots distance from the base of the lateral to a tip or branch point. The original tip and the furthest from the base is shown by an open circle. The second tip that resulted from the first branching is shown by an open square. The first branch point is shown by an open triangle. The tip that results from the second split is indicated by a filled circle and the second branch-point by a filled triangle. Note that the distance between all of these landmarks and the base and from one another increases over time. A cartoon is also present showing a lateral prior to branching and shortly after branching. Three models are presented for subsequent elongation. In growth is restricted to the distal tip (represented by filled areas). This leads to no movement of the branch-points but an increase in the lengths of the arms. In ß growth is restricted to the base of the lateral. This leads to an increase in the distance from the base of the lateral to the proximal branch-point. No increase is seen in the length of the arms or of the distance between the branch-points. In growth is distributed throughout the lateral and there is an increase in the distance of the branch points to the base, between the two branch points and in the lengths of the arms. In growth takes place at both the base and at the distal tip. There is an increase in the distance from the base to the branch points but no increase in the distance between the branch points. There is an increase in the lengths of the arms. Our observations routinely fit the model shown in .

Return to article