Olivier Perru

Our paper focuses on the theory of bud’s development in some works of the french botanist Aubert A. du Petit Thonars (1758–1831). From 1792 to 1801, he was a botanist traveller, visiting Tristan d’Acugna, Le Cap, Madagascar and L’Isle Bourbon, and he observed the growth of tropical trees. He concluded that, on the bark, many buds produced some bundles of fibres. He repeated his observations and experiments with European trees in France. For him, the bud’s activity produces fibres. Collections of fibres cause a organic unity. Du Petit Thouars carried on with the studies of Duhamel du Monceau about wood and bark. He discovered that these two vegetal tissues were independent, but grew from the same matter, which was called “cambium” by Duhamel du Monceau in 1758. Our botanist’s opinions and observations were discussed and his point of view was sternly combatted by the French physiologist Brisseau-Mirbel, but it was taken up again by Moquin-Tandon. Finally, the cellular theory and discoveries of vegetal tissues proved Brisseau-Mirbel right about building up of plants: they are made up of cells but they are not a composition of fibres.

Résumé Dans cet article, nous examinons la Démonstration de l’existence de Dieu de Fénelon ; la question posée est celle de la démarche apologétique, où le spectacle de la nature donne à voir l’activité du Créateur. Dans un regard qui suppose la foi, Fénelon met en relation le caractère admirable de l’ordre du monde et ce Dieu que nul ne conteste encore sérieusement. Réenchantant l’univers mécaniste, Fénelon en appelle à un Dieu seul capable de mettre en harmonie le mécanisme et la vie ainsi que le corps et l’âme. À la lumière de la science du temps, les espèces animales s’inscrivent dans un ordre équilibré et vivant, le corps organisé est le siège d’opérations d’assimilation et de génération, inaccessibles à la machine, il semble aussi fournir le support des pensées à l’âme. Faute de l’existence d’une cause assumant simultanément les dimensions matérielles, vitales et spirituelles, le lecteur se trouve renvoyé à l’action divine. S’agit-il ici d’occasionalisme fénelonien? Peut-on parler de postérité de Fénelon dans le discours sur la nature au xviii e siècle?

The aim of this paper is an epistemological analysis of mutualism modeling. From the Lotka-Volterra analysis, we look for some characteristics and epistemological inadequacies of this class of models. Volterra s’mathematical work was a response to a particular ecological situation. This situation is the rupture of the equilibrium between competing associated species. Starting from equations describing variations in competing populations, a change of sign is enough to transform them into equations describing variations in numbers of mutualistic populations. In terms of modeling, competition models have attracted a lot of attention while mutualism has been relatively neglected. If the relative growths of the two populations are the same, applied to mutualism Lotka-Volterra models indicate an equilibrium point. These models are used to make a distinction between obligatory and accidental mutualism. To be considered valid these models need to give an equilibrium point and provide the dominant characteristic of biological mutualism (obligatory or accidental). From the end of the 90s, some researchers have developed more realistic bio­logical models that allow a transition from parasitism to mutualism depending on the densities of the two partners. From an epistemological viewpoint, these models remain relative to a population level. They refer to the biological pop­ulations studies but they need to be complemented by an analysis of the same biological phenomenon at an individual level.