[axscientist (OP)]

What are pith rays and vascular rays? What are their differences?

Thanks,
AX

[Colin2B]

What are pith rays and vascular rays? What are their differences?

Thanks,
AX

They are really the same, properly called Medullary rays.
They are lines of cells found in some species of tree and run radially - centre to edge. They are used to transport water & minerals across the tree. 
If the wood is quarter sawn - perpendicular to the growth rings - they show as patterns (sometimes called figure) which often are very attractive as they reflect light.
Look at some oak panelling, you will see light streaks in the wood.