[away3d] how to modify vertex of a primitive

[tain]

hi,
i wanted to create 3d ribbons in away3d and i found problems at very
basic things.

when i create plane with,

 var plane:Object3D = new Plane(.......);

and try to trace(plane.vertices); it says 'vertices' are not defined.

i see in examples just to write myObject.vertices[x] to access the
vertex but that aint working.
so how can i access a vertex?