Abstract
Detailed growth paths of embryonic frog and chick axons were measured as the axons elongated in dispersed cultures on acid-rinsed glass surfaces. Mathematical analyses demonstrate that, under these conditions, axons do not grow randomly but tend to grow straight. Growth cones appear to actively alternate sides--right and left from the straight line of growth--and the growth cone neck exhibits all possible angles, but the axon itself maintains a fairly constant orientation. It appears that an axonal resistance to bending may be the cause of the intrinsic tendency for relatively straight axonal growth. The natural straightness of axonal growth may be an important developmental determinant of certain in vivo axon patterns.