Abstract
The veins of plant leaves exhibit a large variety of morphologies often
thought to result from their growth in a concentration scalar field.
It is shown here that the topology of these patterns rather corresponds
to what is expected from growth in a tensorial stress field. This
is demonstrated by analogic experiments performed on crack formation in
gel films where many characteristic venation patterns, of both dicotyledons
and monocotyledons, could be reproduced. This suggests, for the origin
of the veins formation, a set of hypotheses which is new but supported
by known physiological data.