Table S1.

Table of statistics detailing processing of tracks

Tracking statistics	10 μM	20 μM	30 μM
Total time, s	7,458	5,534	3,130
Threshold for identifying tracking errors, nm	300	550	700
Total time after removal of poorly tracked episodes, s	7,358	4,979	2,684
Average no. of tracking errors remaining per track	2	2	3
No. of slow growth episodes	2	3	5
Total time after removal of slow growth episodes, s	7,339	4,889	2,521
% Total time remaining	98	88	81

Tracking statistics for three experimental conditions: 10 μM, 20 μM, and 30 μM tubulin. Tracking errors were identified as deviations from constant growth above a threshold value. Errors often appeared consecutively and so poorly tracked episodes were removed from the data entirely. The tracking errors remaining per track were then corrected. In the second step slow growth episodes were identified and also removed from the data (SI Materials and Methods and Fig. S2).