  A fundamental question regarding biological transport networks is the
interplay between the network development or reorganization and the flows it
carries. We use Physarum polycephalum, a true slime mould with a transport
network which adapts quickly to change of external conditions, as a biological
model to make progress in this question. We explore the network emergence and
reorganization in specimens suddenly confined in chambers with ring geometry.
Using an image analysis method based on the structure tensor, we quantify the
emergence and directionality of the network. We show that confinement induces a
reorganization of the network with a typical $10^{4}$s timescale, during which
veins align orthoradially along the ring. We show that this network evolution
relies on local dynamics.
