Article also published in shortened form under the title ‘Hygienic strategies, a stroll through the grounds of Cerisy’ in La Part de l'œil no. 40 – 2026; Le Geste et la Figure – Michel Guérin, l’affectivité de la pensée.

As early as 1866, the Finnish botanist Wilhem Nylander wrote that "lichens, in their own way, give a measure of the healthiness of the air, and constitute a kind of very sensitive 'hygiometre' ". Strangely enough, until recently, this analysis, which coincided with industrialisation, remained the preserve of specialists in lichenology.

Lichens perceive a quality that escapes human sensitivity and even, to some extent, the technical nature of its measurements: the properties of the atmosphere. But we don't all breathe the same air, and access to it is very unevenly distributed around the world. If we look at air quality not just in terms of its purity, it tells us something about the environment as it is changing under the impact of globalised extractivist capitalism.

This research project involves working with lichens to produce, with them and the scientists who study them, a representation of different atmospheres that can be compared. Giving shape to the quality of this collaboration, making it perceptible, is like the way lichens are affected by air quality.

Neither objects of scientific knowledge nor objects of aesthetic delight, lichens here are subjects who produce knowledge and form. Their nature implies a re-evaluation of the dominant role of theoretical knowledge and vision in favour of a less centralised perception: moving around following the order of lichen colonies. The walks are envisaged as possible knowledge resulting from collaborative work: a kinesthetic knowledge of the atmosphere.

If the mapping proves possible, and if it can be transferred to another territory, then the differences and similarities that the comparison will allow will be a way of giving shape to the inequality observed in access to the air, and therefore of including it in our perceptions.