Table 1.

Average times until catastrophe (seconds)

Tubulin concentration (mg/ml)	Chromosome bound (s)	Free ends (s)
0.75	1470  (n = 5)	627  (n = 12)
1.00	1211  (n = 9)	516  (n = 9)

The average time until catastrophe at the chromosome-bound ends of microtubules was estimated by dividing the total time that the bright segments on these microtubules were observed moving away from chromosomes by the number (n) of times that these segments switched to movement toward a chromosome. The average time until catastrophe at the free ends of microtubules was calculated by dividing the total time that all microtubules grown from axonemes were observed by the number (n) of times these microtubules switched to rapid shortening.