This series was created in abandoned exercise yards of the santé prison in Paris. Like a botanist creating his plant illustrations, Mathieu Pernot methodically photographs the different invasive specimens that have grown in that restricted space. They make up, with the prison architecture, a strange ecosystem: they oppose it as the biological order opposes the instituted order, and as the force of nature opposes that of the law; they bring to mind the presence of the prisoners whose walks are in fact limited to these stone quadrilaterals, but they suggest too that some elements of life can appear in prison that are capable of weakening its foundations.