  We present a study of the in-plane and out-of-plane magnetoresistance (MR) in
heavily-underdoped, antiferromagnetic YBa_{2}Cu_{3}O_{6+x}, which reveals a
variety of striking features. The in-plane MR demonstrates a "d-wave"-like
anisotropy upon rotating the magnetic field H within the ab plane. With
decreasing temperature below 20-25 K, the system acquires memory: exposing a
crystal to the magnetic field results in a persistent in-plane resistivity
anisotropy. The overall features can be explained by assuming that the CuO_2
planes contain a developed array of stripes accommodating the doped holes, and
that the MR is associated with the field-induced topological ordering of the
stripes.
