Same Machine, Different Structure: Animal-Plant Analogy in Cartesian Mechanical Physiology
p. 225-245
Résumés
Abstract. The test of the Cartesian mechanism puts in crisis the plant analogy that had just regained momentum in early modernity. By representing the living body as a machine, Descartes (apparently) sacrificed the study of plants in his natural philosophy. However, when his mechanistic analogy lags behind his physiological explanation, the comparison between plants and animals resurfaces and reveals its originality. First, Descartes defines plants as hydraulic machines (just like animals); second, he uses the animal explanation to describe plants; third, he describes structural differences between living bodies. If the same mechanical laws are applicable to bodies, a mechanical gradation unfolds between plants and animals. Then the Cartesians in turn assume the same distinction when they propose a plant-animal analogy as part of the philosophical mechanism that determines modern culture.
Résumé. L’épreuve du mécanisme cartésien met en crise l’analogie végétale qui vient de retrouver un nouvel élan au début de la modernité. En représentant le corps vivant comme une machine, Descartes sacrifie (apparemment) l’étude des plantes dans sa philosophie naturelle. Pourtant, lorsque son analogie mécaniste marque le pas dans son explication physiologique, la comparaison entre plantes et animaux ressurgit et révèle son originalité. Premièrement, Descartes définit les végétaux comme des machines hydrauliques (tout comme les animaux) ; deuxièmement, il utilise l’explication animale pour décrire les végétaux ; troisièmement, il décrit des différences structurales entre les corps vivants. Si les mêmes lois mécaniques sont applicables aux corps, une gradation mécanique se déploie entre plantes et animaux. Ensuite, les Cartésiens assument à leur tour la même distinction lorsqu’ils proposent une analogie plantes-animaux dans le cadre du mécanisme philosophique qui détermine la culture moderne.
Texte intégral
Introduction
1In René Descartes’ (1596-1650) natural philosophy, the study of the human body develops significantly from the analogy with machines. In following a mechanical program, Descartes left aside another analogy, namely the one between plants and animals that was acquiring momentum in early modern culture. Although in the Discours de la Méthode (1637) Descartes suggests that the circulatory system has an arboreal structure, he does not aim at a more consistent interpretation of plants as models for describing the animal body2. In early modern medicine and natural philosophy, this comparison was indeed widespread as an analogy, as it underlies the uses of the structure and functions of plants as a model to describe the animal body, which ultimately led to comparative anatomy. When Descartes describes the functioning of plants in mechanical terms in his later notes, he somehow makes them analogous to animals, yet problems remain. Questions concerning this association in the mechanistic terms of the Cartesian philosophy of nature are: (1) are plants and animals similar machines? And, (2) is it possible to explain living functions by means of the analogy between plants and animals? Answering these questions is difficult, as I will investigate in this chapter, while uncovering the conflict between the mechanical program and the uses of vegetal analogies.
2In the next section of this chapter, I provide an overview of the analogy between plants and animals in late sixteenth and early seventeenth century medicine, mainly focusing on the reappraisal of a Galenic tenet, and natural philosophy, especially in the texts of Andrea Cesalpino (1524/1625-1603) and Giambattista della Porta (1535-1615)3. Then, I will discuss Descartes’ attempts to describe plants within a mechanical framework. Although he gathers plants together with animals, his interpretation of these bodies as analogous is not always linear. Finally, I will explore how far Cartesian scholars from different contexts, namely, Henricus Regius (or Hendrik de Roy, 1598-1679), Johannes Clauberg (1622-1665), and Pierre-Sylvain Régis (1632-1707), claimed that both similarities (in the mechanical functioning) and dissimilarities (in the architectural structure) surface between plants and animals. While the same mechanical laws of nature apply to all living bodies, and sometimes plants are an apt model for explaining animal functions, Cartesian scholars acknowledged differences in structure that made it difficult to unfold a comparative anatomy as physicians in the second half of the seventeenth century tended to do.
The Early Modern Context: Botany, Medicine, and Natural Philosophy
3Besides the analogy between plants and the vessels in animal bodies, which populated medical texts at large, the rediscovery of Galenic embryological work spurred new attention to plants as models for knowing animal physiology. Indeed, physicians from different contexts, such as André du Laurens (1558-1609), Hieronymus Fabricius ab Aquapendente (1533.1619), and Jean Riolan the Younger (1577 or 1580.1657), proposed the tenet that, in the beginning, the fetus lives the life of a plant, as it maintains itself by drawing nutrition from the mother, without the need of a heart. Although this was a popular issue at the time, and it was for example discussed in the Hippocratic tradition, Galen’s work included a more specific interpretation, readily endorsed by such physicians, who tried to accommodate Hippocrates with Galen, as in the case of Riolan. Two aspects characterize Galen’s tenet. The first is that the fetus in the beginning is a plant, and the second stresses that some organs of the abdomen, and specifically the liver, have the same nature of plants4. From the fact that the operations of the fetus were limited to growth alone, one of the functions of the vegetative soul, physicians such as Fabricius claimed that the fetus is ruled by the vegetative soul alone, exactly like plants. Furthermore, since the liver is the first organ to be formed in the fetus, and since it is the seat of the vegetative soul, physicians claimed that it operates similarly to the roots of a plant. More than a simple analogy, physicians seemed to suggest that the fetus lives as a plant, and is a plant altogether, as it is joined and fastened to the umbilical vessels as the roots of plants are fastened to the earth. Within this tradition, representations of the fetus as a plant entered the medical texts of the time, as happened in Adriaan van den Spiegel’s (or Spigelius, 1578–1625) image of the fetus as a cabbage in De formato foetu (1626 – see Figure1)5.
Figure 1. Fetus as a cabbage in van de Spiegel 1631, Tabula IV, p. 36ff.

Source : Femme enceinte dans un paysage, de formato foetu liber singularis. Planche IIII (Francfort : M. Merianus), Van de Spiegel, Adriaan, 1631, © BnF / Gallica.
4This interpretation provided a scientific framework for a popular belief6, which later developed into comparative anatomy. At the time, it contrasted with the Renaissance elaboration of the analogy between animals and plants that developed from the correspondence between bodies. Indeed, by means of subtle clues in the form of signatures, Renaissance scholars uncovered sympathetic correspondences that made it possible (a) to understand the secrets of bodies, (b) to recognize the essential nature of a mineral, plant or animal, and (c) to establish the affinities thereof. The champion of uncovering correspondences was Della Porta, who promoted the doctrine of signatura rerum in his writings. In 1586, he published De Humana physiognomonia, a work devoted to physiognomy7, hypothesizing that the inner nature and disposition of a person could be read in his outward form and lineaments. Parallel to this text, in 1588 he published Phytognomonica8, an investigation into the intimate relations between vegetal and human bodies, that is, a study of the analogies between these different realms of nature. Accordingly, plants possess signatures that reveal their inherent properties and their affinities to the human body, making it possible to apply them to the treatment of various diseases. Among an enormous variety of cases, one could name the citrus, used to treat cardiac diseases. Moreover, the juice of the citrus (probably a lemon) helps control the yellow bile, given the similar color9. Similarly, plants with yellow flowers may be used to treat patients with diseases related to the yellow bile, while plants with red flowers would reduce inflammation in the body. These remedies were widespread at the time, as Della Porta collects the popular beliefs and provides them with a theoretical framework. Phytognomonica had great success and was reprinted throughout the seventeenth century, promoting the analogy between plants and the human body given that their external similarities reveal their internal power or nature.
5A less successful, but nonetheless important attempt to uncover the analogies between plants and the human body is contained in Andrea Cesalpino’s De Plantis libri xvi (1583). This text had indeed little success among naturalists and botanists of the time, although it encompasses botany within an Aristotelian framework. Within this framework, Cesalpino claims the vegetative soul to be the principle of life in plants, whose aim is the conservation of the species, as every part, roots, trunks, branches, leaves, fruits and flowers, is teleologically oriented. The same occurs in animals, as a comparison develops between the structure of plant organs with the structure of the organs of animals10. For example, he claims that the roots are the superior part of plants, developing the traditional claim, originally to be found in Plato’s Timaeus, that plants are inverted humans11. And he then suggests that the movement of food from the bottom to the top of the plant reproduces the movement of food in the human body, from the abdomen to the heart and the head12.
6In this short reconstruction, the analogies between plants and animals present several nuances and follow different paths. Within the Galenic tenet, physicians suggest plant as model for describing the fetus, defining the beginning of life, and expounding the physiology of the liver, and therefore making nutrition as a common activity to all living bodies, while in either alchemical or Aristotelian natural philosophies the animal body is the model describing the nature and virtues of plants. In the first case, the analogy reveals an interconnection between plants and animals according to which, in a certain sense, the human body is a plant. In this sense, there is no separation between the realms of nature. In the second case, the plant is just a simpler case, and traditionally precedes the animal in the scale of beings, but also reveals a correspondence between bodies. From the combination of these strands, comparative anatomy between plants and animals strengthens at the end of the seventeenth century.
Plants as Hydraulic Machines and the Analogy with Animals in Descartes
7Descartes presents a different interpretative line. In his physics, the French philosopher claims that all nature is composed by extended matter alone, and bodies result from the composition of particles that have no qualitative differences. Moreover, since no substantial forms or incorporeal principles differentiate between bodies, no gradation surfaces within the realms of nature. Descartes alleges that all nature operates mechanically, consistently with the mechanical laws of nature13. In this sense, bodies could be described using a mechanical analogy—the animal body is a hydraulic machine like those one finds in gardens and grottos. Yet, a quantitative differentiation surfaces between bodies. In the Discours, for instance, Descartes separates plants and inert bodies from animals, as he claims that he “moved from the study of inanimate bodies and plants […] on to describe animals, and in particular men14.” This text leaves a question unresolved: is this difference only structural, or also mechanical? That is, are plants and animals different in the mechanical terms of Descartes’ physics?
8Although one should tend toward a positive answer, this text appears complex. Descartes gathers plants together with inert bodies, such as meteors, but no discussion of plants surfaces in the essays of 1637, not in his early physics of Le Monde. A similar proximity is proposed in one article of the Principia philosophiae (1644), where Descartes uses vegetation to exemplify one of the cases in which the movement of particles creates fire in dead bodies, that is, the case of stored hay15. In determinate conditions, the movement of spirits and juices within the pores of mown grass produces fire. While describing the internal structures of herbs, in this text Descartes is not claiming an analogy between sap and blood, but merely focuses on the causes of natural fires in inert matter, something that makes vegetation closer to meteors such as salt rather than animal bodies. The case of cut hay has little to do with the living functions of vegetal bodies per se.
9A different interpretation surfaces in the correspondence, where Descartes tends toward a continuity between animals and plants, as he includes plants within living bodies, a position he later endorses in the Principia. In doing so, he suggests plants are similar to animals. In replying to Alphonse Pollot’s (1602-1668) remark that “a more excellent principle than the necessary disposition of their organs, i.e., an instinct that cannot be found in a machine or in a clock”16 should be found in animals, Descartes evokes the case of plants, which nature composes “with an infinity of tiny invisible ducts through which certain juices gradually ascend to the ends of the branches, where they intermingle and combine and dry out in such a way as to form leaves and flowers and fruits17”. Although the analogy between plants and animals is not clearly stated, Descartes describes plants in answer to concerns about the mechanics of animal bodies. Two consequences arise. The first is that the same mechanical laws apply to both plants and animals, which are similar hydraulic machines—he describes the animal body as a hydraulic machine in L’Homme18. The second is that plants are simpler bodies than animals, and in this sense a sort of model he may use to explain the functioning of living nature.
10Yet, this text is important in Descartes’ mechanical program. In taking the identification of plants (and animals) with the machine to its extreme consequences, Descartes entails an ontological identity of machines and living bodies that results in the narrow reduction of the Principia, as Helen Hattab has recently shown. In this text, Descartes claims that
things made by art helped me quite a bit: for I recognize no distinction between them and natural bodies, except that the operations of things made by art are for the most part performed by instruments so large that they can easily be perceived by the senses: indeed this is necessary in order that they may be fabricated by men. By contrast, however, natural effects almost always depend on certain tools so minute that they escape all the senses. There really are no reasons in Mechanics which do not also pertain to Physics, of which it is a part or species: nor is it less natural for a clock composed of these or those wheels to tell the time, than it is for a tree originating from this or that seed to produce a certain kind of fruit. For this reason, just as when those who are trained in considering automata, whenever they know a certain machine and inspect some of its parts, easily conjecture from these parts in what way the others which they do not see are made, so from the sensible effects and parts of bodies I have attempted to investigate which are their causes and insensible particles19.
11Taken alone, this emphatic passage would produce a mechanistic explanation Descartes did not actually aim to; in contrast, as Barnaby Hutchins has revealed, Descartes stops the reduction in physiology where appropriate and reveals a more moderate interpretation20. One should thus nuance this narrow passage with a definition Descartes provides a few pages earlier, where he suggests that, in his natural philosophy he had “considered the shapes, motions and sizes of bodies and examined, according to the laws of Mechanics, confirmed by certain and everyday experiences, what must follow from the mutual concourse of these bodies21.” Accordingly, mechanics works in a demonstrative sense, providing rules or helping visualize invisible parts, but Descartes’ explanation is not utterly mechanistic. On the one hand, Descartes transfers the certainty of mechanical demonstrations and of mechanical rules to physics and physiology. In this sense, animals and plants are like hydraulic machines insofar as they are mechanically build and operate mechanically. Yet, on the other hand, Descartes needs to confirm this mechanistic framework by means of what he calls experience, that is, by observing the physiology of living bodies.
12The inspection of living bodies thus appears crucial. Yet, he does not observe vegetation or animals as separate subjects, but associates the study of plants with the work on animals. This is what he does with Reneri when in 1638 they observed animals and plants together22. While little is known about their observations, Descartes proposed a clearer association between plants and animals in an August 1638 letter to Marin Mersenne (1588-1648) concerning the movement of the leaves of the sensitive herb, or mimosa pudica23. Indeed, Descartes claims to be able to explain the phenomenon of vegetal sensitivity given the fact that the same mechanics regulating animal sensitivity applies to this plant. He writes that:
I do not find anything curious except its rarity; for, having explained the movement of the heart in a way which suits both plants and animals, I will have no difficulty in conceiving how it moves if the same organs can be found in that plant. But I do not want to say more clearly how this movement occurs, if I have not observed or examined it24.
13Accordingly, if confirmed by observations, his mechanical explanation of the heartbeat would fit both plants and animals in a way that makes it possible to expound the movement of the leaves, that is, the physiology of (this) plant. In applying the inductive rule of his method, which consists in finding a point of contact between bodies gathered into different classes, Descartes suggests either that plants and animals fall within the same class of bodies, or that it is possible to define a point of contact between the class of vegetal and animal bodies. In either case, the mechanics of the heartbeat, that is, the circulation of blood, makes these bodies comparable. This is a crucial point as it reveals an originality in comparison with the traditional claim that nutrition makes plants and animals analogous.
14It is to be noted that for Descartes comparisons are a strong heuristic tool to understand through analogies, which are only possible between homogenous bodies25. In this sense, being subjects of analogies, plants and animals are homogeneous, that is, mechanically similar. Yet, the text contains something more. The analogy is not constructed from plants to animals, but the induction works from animals to plants, insofar as Descartes conceives of plants to display a similar activity to the one common in animals. The mechanics of the animal body, and the circulatory system in particular, is thus the model to describe all living nature. While pursuing some observations of the sensitive herb, Descartes finds an analogy with the animal body, showing the animal-plant continuity within his mechanical system.
15In sum, Descartes observes plants together with animals, ultimately claiming that their structures and their physiologies are mechanically similar: they are hydraulic machines activated by a source of heat. Yet, while he fails to expound the sensitive phenomenon of the mimosa pudica, the analogy between plants and animals through the circulation of liquids appears at a stalemate. As he attempts to explain the vegetal life of plants in his biomedical notes, his interpretation changes.
Where the Analogy Ends: Differences between Plants and Animals
16In the notes on plants collected in the Excerpta anatomica, Descartes explores the structure and operations of vegetal bodies in more detail. Two notes are particularly significant as in describing the basic activities of life, Descartes uncovers an analogy between plants and animals. Yet, these notes present a different focus. The first note concerns nutrition and growth, it is dated November 1637 and entitled “On accretion and nutrition”. Descartes mechanically differentiates between inert and living bodies: the former only grow by the external apposition or juxtaposition of particles, as occurs during fossilization, while the latter grow through an internal change of particles, i.e., nutrition26. This second operation occurs in animals and plants (and human bodies, of course). Throughout the note, Descartes refers to animals and plants, correlating such parts as “hair, fur, nails, horns, mushrooms, tubers and all the parts of animals and plants” but also “plants without seed and […] imperfect animals, such as oysters”27. Then, he relates “the wood, the bark, the roots, leaves, flowers, fruits, etc. in plants [with] the limbs, bones, brain, membranes, and blood, etc. in animals”28. The same mechanics, that is, the internal change of particles, or the immutatio, makes plants and animals comparable. In nutrition, plants and animals are thus mechanically analogous, a point he will later suggest in La Description du corps humain29.
17The second note concerns generation. This is the text:
The formation of plants and animals is similar by taking place through the circular movement of particles of matter under the force of heat; but it differs in that, in the generation of plants, the particles of matter revolve circularly, while those particle generating animals revolve spherically and in all parts.30
18As for nutrition, a mechanical analogy between plants and animals surfaces in generation. In both bodies, the mechanics of motions activated by the force of heat and the arrangement and motions of particles similarly operate forming the body31. Still, Descartes never speaks of circulation in this case. Moreover, Descartes differentiates between plants and animals. In the first case, particles only move circularly, while in animal bodies particles move spherically. This is a meaningful, though difficult differentiation. Let us try to deal with it.
19While specifying that the same mechanical framework regulates the generation of plants and animals, whose motions are consistent with the theory of vortices, Descartes posits a geometrical difference between generation in plants and animals. In looking at the images in the Appendix of the Excerpta anatomica, this differentiation is more intelligible – see Figure 2.
Figure 2. On the left, Figure XXII, formation of plants; on the right, Figure xxii bis, the formation of animals, from Descartes, Excerpta anatomica, AT xi Appendix.

Source : © BnF / Gallica.
20On the left, particles compose a plant from the seed, that is, moving from the ground to compose the bark (particles revolve circularly from points a to b in the figure), the branches (particles move towards the top forming a circle, points d and g in the figure), or the roots (points c and f in the figure). In composing plants, particles follow a centrifugal motion, proceeding from the centre to the external part of the plant. On the right, the movement of particles is much more complex. According to Descartes’ explanation, particles move spherically in composing an external membrane (ii in the figure), within which particles continue moving centripetally, that is around a central fulcrum. In the figure, the fulcrum is the pipe “lk, that represents the oesophagus”, then the more lighter particles move towards “m, where they compose the brain; while the coarser parts […] towards n, where they produce the liver and the spleen”32, then the more agitated particles compose the circulatory system and the heart, o. The difference in motions results from the difference in matter composing vegetal and animal seeds. This is consistent with the rules of motion of Descartes’ physics: solid particles (like those of the seeds of plants) only move circularly, while most fluid particles (like the seed or semen in animals) move spherically33. The first move centrifugally, while the second move centripetally. As a result, they compose very different bodies.
21While the same mechanics applies to animals and plants, a difference in the structure of these bodies surfaces. This difference is both external—plants are attached to the ground, while animals are free to move—and internal: plants are mostly composed of channels and particles that move from the bottom to the top of the plant, while animals have several organs and a more complex structure, in which particles move following different paths.
22What results is that, on the one hand, plants and animals are analogous bodies, and Descartes accounts for them as similar hydraulic machines. Indeed, the same mechanical laws regulate their functioning and frame the study of them. Moreover, being simpler bodies, plants help account for the basic activities of life, those which a strong mechanization fails to describe, since machines do not grow nor breed. Yet, on the other hand, plants and animals have different structures, and a mechanical gradation arises in Descartes’ notes. If this is not a scale of being in Aristotelian terms, it is however a significant differentiation in the mechanics of living bodies that makes plants occupy a first step and animals a subsequent step. Zoophytes such as the mimosa pudica stand, somehow, in between.
23In sum, Descartes seems to follow an original interpretative line. First, following his inductive method, he describes plants using the mechanics of animals as a model, that is using circulation as a common activity to make living bodies comparable. Second, as he observes plants with more attention, his interpretation slightly changes. He uses plants to describe the basic functions of life, i.e., generation, nutrition, and growth, making plants as a useful model to explain vegetative functions. When he speaks of an internal movement of particles, he avoids any more clear connection to the heartbeat. Third, he differentiates between plants and animals, which are mechanically similar, but structurally different. While plants and animals are similar hydraulic machines, and analogies can be drawn to shape knowledge of vegetative activities, differences surface in these bodies. One is evident in the case of the mimosa pudica, where no heartbeat could be detected and no clear circulation emerges in plants. In the end, since he did not provide a complete section on animals and plants in the Principia philosophiae, this original analogy lags unspecified.
The Analogies and Differences between Plants and Animals in Cartesian Tradition
24Cartesian scholars developed the study of plants within Descartes’ mechanical framework and included a section on vegetal bodies in their texts. Yet, while they underlined the similarities between plants and animals, they also tended to produce separate accounts of these bodies. In this section, I analyse three cases. The first case is Henricus Regius, a very early proponent of Cartesian natural philosophy. In Philosophia naturalis (1661 [1654], but a first, smaller edition was published in 1647 with the title Fundamenta Physices), Regius provides a complete natural philosophy that, in book 4, includes sections on plants and animals. First, he defines living bodies as those “whose parts are temperate and conformed in such a way that their bodily substance, which is perpetually dissipated, is conserved by means of the fluid prepared and infused from the inside, following the mixture of temperaments and the conformation of parts”34. Within this mechanical frame, the conservation of life through nutrition and the procreation of life through generation characterize living bodies in general. Both activities depend on the vegetative soul and follow the mechanical laws of nature, a constant condition in the generation of plants and animals35. Yet, he separates the chapters on plants (De stirpibus, chapter 2) and those concerning the functions of animal bodies (chapters 3-17). Although the same mechanics applies to living bodies, plants and animals are indeed different—it is also to be noted that Regius describes animals as automata, while this term is not present in the chapter on plants.
25In chapter 15 on animal generation, Regius adds a few references to plants36. However, Regius does not develop an analogy between these bodies, but only claims that what happens in the seed of plants similarly occurs in animal semen, without specifying this similarity any further. In chapter 17, Regius describes bodies standing in between plants and animals, namely zoophytes, such as the creatures that live in shells, spoons, herba viva, herba mimosa, and so on37. While providing a mechanical explanation of the phenomenon of vegetal sensitivity that is not inconsistent with animal sensitivity, Regius does not suggest any clear analogy with the animal body. If in Descartes the mimosa pudica should have similar organs to animals, in Regius this plant is only remotely similar to animals, as he never suggests any mechanical, structural, or functional identity, but merely claims the plant to be a hydraulic machine.
26Despite claiming that animals do not live in the manner of plants, but through sensation and motion38, and clearly separating plants from animals, Johannes Clauberg presents several similarities between living bodies in Physica quibus rerum corporearum (1664). Although he refrains from stating any clear analogy, Clauberg repeats the rhetorical (and traditional) claim of humans as inverted trees39, acknowledges mechanical similarities, and gathers animals and plants together in his description of the vegetative activities, nutrition, growth, and generation. First, in suggesting that plants and animals have a precise figure, Clauberg especially claims that living bodies significantly differ from non-living bodies such as stones, metals, and fossils40. Then, Clauberg describes the similarities in the parts of plants and animals. For example, he stresses that organic bodies have organs, such as roots, stalk or stem, branches, shoots, etc. in plants [in Planta radix, caulis, ramus, surculus &c.], or head, bones, abdomen, etc. in animals41; he speaks of a texture one may find in corpses or dead plants42, and later describes leaves and fruits together with the fur, feathers, and horns in animals43, just to name a few aspects.
27When he comes to describe the vegetative activities, Clauberg stresses a similarity between what one sees in seeds, that is the primordium of a plant, and what one sees in the eggs of chickens44. Then, in describing the ways plants draw food from the soil and nurture, Clauberg suggests that a similar operation occurs with the foetus drawing food from the mother45. However, in all these issues, he never goes into the use of plants as analogous to describing the animal body, and merely describes a mechanical similarity. For example, as he describes the movement of juices within plants, which ascend to the top of plants, Clauberg describes the circulatory movement of blood in animals, but refrains from suggesting a clear analogy between sap and blood46.
28In sum, Clauberg claims that several similarities surface between plants and animals, from heat as the cause of life to the morphologies of parts, and finally to several vegetative activities. In this way, he follows Descartes’ attempt to gather plants and animals together. Yet, he avoids discussing these similarities in detail, and refrains from making plants as analogous of, if not a model for studying the physiology of animals.
29In the monumental Cours entier de philosophie, or Système général selon les principes de Descartes (1690, published in 3 volumes), Pierre-Sylvain Régis presented the entire philosophy of nature in Cartesian term. Régis’ sixth book concerns plants, while in the seventh book he deals with animals. In the Preface to the sixth book, Régis summarizes the mechanization of plants, whose life consists in nutrition and in the disposition of particles according to their size and figure47. While nutrition occurs through the movement of sap throughout the plant, Régis endorses Marcello Malpighi’s (1628-1694) position, and claims that the circulation of juices in plants is not very different from the circulation of blood in animals, “at least for what concerns the necessity of the preparation that aliments require by means of this Circulation: because it is easy to show that all the conditions making Circulation necessary for the nourishment of Animals are to be found in the nutrition of Plants”48. Indeed, since the similar parts of organic bodies [les parties similaires dont les organiques sont composées] are similar in plants and animals49, one could easily observe in plants the dissipation of nutrients, when they wither and dry out as they are torn from the soil, which dead animals do not do50. In this sense, plants are a perfect case study to understand what happens when living bodies die.
30Yet, against the argument that in plants the organs of circulation are absent (or invisible51), Régis replies that “there are imperfect animals (like the majority of insects) in which one does not observe a vascular system [circulating] the blood, [and also] in which one does not perceive [distinguer] the heart, the liver, nor any other parts generally considered as an organ for the circulation of blood, but this does not prevent anyone to claim that insects have the organs of circulation like perfect Animals”52. The same is true for nutrition and growth, as in the book on animals he claims that beasts nurture like plants53. For example, while stones, metals, and dead bodies grow by a mere (external) juxtaposition of particles, Régis claims that plants and animals grow by an internal accretion, what he calls Intussusception54. This is the Scholastic term to describe the mechanical activity Descartes had named Immutatio in the text mentioned earlier. What is important for us is that, according to Régis the same mechanics applies to animals and plants. In other words, while the organs of animals (such as the heart, the liver, or the stomach) cannot be detected in plants, as they have different structures, nature has, however, endowed plants with the means to perform these activities, that is, they are mechanically similar.
31In this sense, Régis follows Descartes’ approach to living nature, as he embeds bodies within a general mechanical framework, and makes bodies mechanically similar, but then acknowledges that animals and plants are different in their structures. In general, this is the same interpretative line of the three Cartesian scholars examined in this section. All of them endorse a mechanical explanation of living bodies, but describe plants and animals in separate sections; while highlighting similarities (and sometimes suggesting that it would be possible to use plants as models to describe living activities), they differentiate between plants and animals. In the Cartesian framework, these scholars repeated the analogy between plants and animals that flourished in early modern culture limited to the general mechanical functioning of living bodies, ultimately suggesting that plants and animals are similar hydraulic machines, but also highlighted that important differences between these bodies surface.
Conclusions
32Descartes studied plants in his research on living nature, gathering plants and animals together, as his interest in vegetation appears restricted to providing a mechanical explanation for the basic activities of life, those plants share with animals. Although Descartes suggested circulation is the means to specify an analogy between plants and animals, he did not develop any analogical study in this way, as later physicians such as Malpighi did, nor any comparative anatomy between plants and animals as Herman Boerhaave (1668-1738) later did. While including vegetation within his mechanical framework, Descartes discussed the functions of plants using the mechanics of animals as a model. What regulates the comparison between bodies is, therefore, the mechanical reduction of living bodies to hydraulic machines. In this sense, plants are like animals. In his attempt to explain the phenomenon of the sensitive herb, Descartes claimed that plants and animals share similar functions, namely the heartbeat. Still, he did not explore this analogy further. When he came to study plants in detail, that is in describing generation and nutrition, he claimed a similarity surfaces between animals and plants: the movement of particles activated by a source of heat is a common point in living bodies. Yet, this analogy presents limitations as important differences in the structures of animals and plants arise. At a certain point, the analogy between plants and animals however ends. In the case of generation, both plants and animals are generated through the movement of particles activated by heat, yet these motions are significantly different and this difference reveals the diverse structures of bodies. In sum, while a mechanical comparison could be drawn between plants and animals, differences surface too, and a mechanical gradation of bodies ultimately characterizes Descartes’ natural philosophy.
33A similar interpretation is found in Cartesian scholars such as Regius, Clauberg, and Régis, whose natural philosophical texts include relevant sections on plants (whose mechanization is definitely meaningful), in which they repeated both the analogy and the structural differences between plants and animals. Yet, as plants stand between non-living and animal bodies, these scholars elevated vegetation as a crucial body for investigating the basic activities of life. In the mechanical program of Descartes, plants help visualize those operations machines do not reproduce, and in this sense plants are analogous to animals. However, the Cartesians refrain from rejecting the mechanical model altogether and continue discussing plants and animals within the mechanical framework, ultimately revealing gradation and differentiation in living bodies, that is, a mechanical scale of beings. In the end, the mechanical understanding of bodies shapes the knowledge of living nature, also shaping the relationship between animals and plants. This position is original, and somehow anticipates the interpretation of living bodies of the early eighteenth century.
Bibliographie
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Aucante, Vincent. La philosophie médicale de Descartes. Paris: PUF, 2006.
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10.1007/978-3-030-69709-9 :Notes de bas de page
2 See Discours de la Méthode, AT vi, 47 : “à savoir la veine cave, qui est […] comme le tronc de l’arbre dont toutes les autres veines du corps sont le branches”.
3 For a general overview, see Baldassarri, 2022a. A third group surfaces, composed of physicians such as Andreas Vesalius, Charles Estienne, et Jean Fernel. On these cases, see the contributions of Sarah Carvallo and Benny Goldberg in this volume.
4 See Vinkenstejin, 2021.
5 On the reinterpretation of Galen’s tenet in early modern medicine, see Deer Richardson, 2018, 61-74, Baldassarri, 2022b.
6 See Brancher, 2015, pp. 218-224.
7 On physiognomy in the Renaissance, see Giglioni, 2019.
8 See Tongiorgi Tomasi and Willis, 2009.
9 See Baldassarri, 2022c.
10 See Repici, 2005, pp. 72-73. On Cesalpino, see the contribution of Corentin Tresnie and Quentin Hiernaux in this volume. See also Baldassarri and Martin 2023.
11 Cesalpino, 1583, p. 2: “quomodo in animalibus pars superior & inferior accipitur. Verum si nutritionis modum inspexerimus, alio modo partem superiorem inferioremque statuemus.”
12 Cesalpino, 1583, p. 2: “Cum enim tam in animalibus quam in plantis nutrimentum sursum feratur, leve enuim est, quod nutrit, utpote quod à calididate sursum ducitur: radices in inferiori parte implantati necesse fuit, caulem autem recta sursum attolli: nam et in animalibus venatur radicatio in inferiori ventre est, caudex autem sursum petit ad cor et caput.” (French translation in Delaporte, 1979, p. 30.)
13 Cf. Brown and Normore, 2020.
14 Discours de la Méthode, AT vi, 47. Translation is from CSM i, p. 134.
15 Principia philosophiae iv, art. 92, AT viii-1 256. See Gaukroger, 2002, p. 187. Baldassarri, 2019, pp. 42-43.
16 Pollot to Reneri for Descartes, February 1638, AT i 512. Translation is mine.
17 Descartes to Reneri for Pollot, April or May 1638, AT ii 40-41. Translation is mine. Cf. Baldassarri, 2019, pp. 46-47.
18 L’Homme, AT xi 131. It is to be noted that a clear description of plants as hydraulic machines is in Excerpta anatomica, AT xi 627-629. See Baldassarri, 2019, pp. 55-57.
19 Principia philosophiae iv, art. 203, AT viii-1, 326. Italics added. See Hattab, 2019, pp. 127-128.
20 Hutchins, 2015.
21 Principia philosophiae iv, art. 200, AT viii-1, 323, emphasis added.
22 Baldassarri, 2020. Buning, 2013.
23 On the mimosa pudica in early modern times, see Giglioni, 2018.
24 Descartes to Mersenne, 23 August 1638, AT ii 329. Translation is mine.
25 Descartes to Morin, 12 September 1648, AT ii 367-369. Cf. Savini, 2008, p. 132.
26 See Baldassarri, 2019, pp. 53-54.
27 Excerpta anatomica, AT xi 597. Translation is mine.
28 Excertpa anatomica, AT xi 598. Translation is mine.
29 La Description du corps humain, iii, art. 20, AT xi 247: “il faut considérer que les parties de tous les Corps qui ont vie, et qui s’entretiennent par la nourriture, c’est-à-dire des Animaux et des plantes, sont en continuel changement”.
30 Primae Cogitationes circa generatione animalium, AT xi 534; Excerpta anatomica, AT xi 595. Translation is mine. See Baldassarri, 2019, pp. 48-53. See Aucante, 2000, pp. 53-55.
31 See also Baldassarri, 2018, pp. 83-87.
32 Excerpta anatomica, AT xi 595; Primae Cogitationes, AT xi 535. Translation is mine.
33 See Principia philosophiae, iii, art. 52, AT viii-1 105, 107, 148. Principes de la philosophie, iv, art. 19, AT xi -2 210. On the differences in seeds, see La Description du corps humain, iv, AT xi 253: “touchant la figure et l’arrangement des particules de la semence, il me suffit de dire que celle des plantes étant dure et solide, peut avoir ses parties arrangées et situées d’une certaine façon, qui ne saurait être changée que cela ne les rende inutiles; mais qu’il n’en est pas de même de celle des Animaux, laquelle étant fort fluide, et produite ordinairement par la conjonction des deux sexes, semble n’être qu’un mélange confus de deux liqueurs…”
34 Regius, 1661, lib. iv, ch. 1, p. 258. Transaltion is mine.
35 Regius, 1661, lib. iv, ch. 1, p. 260: “Atque hoc in omnium stirpium & animalium generatione, postea explicanda, semper repetitum volo”.
36 Regius, 1661, lib. iv, ch. 15, p. 345, 346, 349, 354.
37 Regius, 1661, lib. iv, ch. 17, p. 389. See Giglioni, 2018.
38 Cf. Clauberg, 1664, Theoriae corporum viventium, xxi, 449, p. 313: “449. In Animali non modo vitam, quemadmodum in Planta, verum etiam sensum & motum considerare solemus”.
39 Clauberg, 1664, Disputationes physicae i, p. 90: “cum radix in arbore, capiti & ori in homine, secundum vulgarem plantae inversae atque hominis comparationem, respondeat”. Cf. Clauberg, 1664, Theoriae corporum viventium, xvi, 333, p. 306: “Sic autem inversa planta cum Homine comparator”. See the contribution by Alice Laforêt in this volume.
40 Cf. Clauberg, 1664, Theoriae corporum viventium, ii, 6, p. 283.
41 Cf. Clauberg, 1664, Theoriae corporum viventium, ii, 7, p. 283.
42 Cf. Clauberg, 1664, Theoriae corporum viventium, ii, 10, p. 284.
43 Cf. Clauberg, 1664, Theoriae corporum viventium, iv, 60, 88 p. 288, pp. 289-290; xi, 218, p. 299.
44 Cf. Clauberg, 1664, Theoriae corporum viventium, xii, 233-234, p. 300.
45 Cf. Clauberg, 1664, Theoriae corporum viventium, xv, 311-314, p. 305.
46 Cf. Clauberg, 1664, Theoriae corporum viventium, x, 186, pp. 296-297.
47 Régis, 1690, vol. 2, p. 464.
48 Régis, 1690, vol. 2, p. 465. Translation is mine. See Régis, 1690, vol. 2, pp. 489-490, 491-492.
49 Régis, 1690, vol. 2, p. 599.
50 Régis, 1690, vol. 2, p. 465: “la dissipation de leur substance paroît visiblement, lors qu’elles se fanent & se desechent, on peut même insérer la promptitude de leur dissipation, de ce qu’elles se sechent plutôt quand elles sont arrachées de la Terre, que les Animaux ne font quand ils sont morts.”
51 Régis claims that some parts of plants operate like the heart of animals, see Régis, 1690, vol. 2, pp. 490-491.
52 Régis, 1690, vol. 2, p. 465. Translation is mine and slightly adapted.
53 Régis, 1690, vol. 2, p. 598-599: “les bêtes ne se nourrissent pas autrement que les plantes […] même en ce qui appartient à la manière dont la nature se sert pour rendre cet aliment propre à les nourrir […] ce changement de l’aliment demande qu’il soit circulé dans les plantes, sont communes aux animaux qui, bien qu’il prennent leur nourriture d’une façon différente des plantes, ne laissent pas néanmoins de se nourrir d’une manière toute semblable.”
54 Régis, 1690, vol. 2, p. 475: “les Racines ne croissent pas comme les pierres par cette sorte d’accroissement qu’on appelle juxtaposition, par lequel les nouvelles parties ne font que s’unir extérieurement aux premieres; mais par cet accroissement qu’on appelle Intussusception, par lequel les parties s’unissent aux parties intérieurement…” Italics in the text. I thank Stefan Heßbrüggen-Walter for having shared with me his “Growing Substance: ‘Intussumption’ in the Late Sixteenth Century,” unpublished. See Baldassarri 2021.
Auteur
-
Fabrizio Baldassarri
Marie Sklodovska Curie, Ca’ Foscari Université de Venise et Université de l'Indiana Bloomington
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