Aristotle’s Conception of Carnivorous Plants as Animals

(What follows is an excerpt from my paper for PHIL481: Aristotle’s Invention of Biology, lectured by Professor Falcon)

Having briefly spoken of the ways in which plant life differs from animal life in both nutrition and reproduction, let us now proceed to the discussions of so called ‘borderline cases’ for Aristotle. For these illustrate interesting insights as to those creatures that are intermediate between animals and plants, such as testacea and carnivorous plants. Even though Aristotle probably did not know about carnivorous plants, such as sundews and venus flytraps, by pointing out the features he explains about these borderline cases, I will here argue that had he known about the carnivorous plants, he would have necessarily categorized them as animals, and not as plants.

Interesting cases may be made about the case of carnivorous plants if one were to follow Aristotle’s taxonomy of plants and animals. For what can be said about them? Carnivorous plants take in food that is undigested, just as animals, and they take in food from the lower part of their body, i.e. leaves. Furthermore, they even seem to possess a sense of touch, for the way they capture insects and the like (as food) is by their leaf’s – or tentacles – being stimulated by a contact with certain objects. Clearly, these facts seem to meet the criteria for being an animal. Let us look at what Aristotle says about teataceous animals, for they are animals but with characteristics of plants. If we know how he is able to classify ceatacea as animals rather than plants, we might gain insight as to how he would have classified carnivorous plants as well. In GA Book I and Book III, Aristotle talks of the characteristic features of testaceous animals. He says that they are “intermediate between animals and plants, [and] perform the function of neither class as belonging to both. As plants they have no sexes, and one does not generate in another; as animals they do not bear fruit from themselves like plants.” At another place, he describes them as “compared with animals they resemble plants, compared with plants they resemble animals,” and that some “are produced from seeds, some from slips, planted out, some by budding off alongside, as the class of onions.” Further, in HA Aristotle discusses about testaceans as non-copulative species, and that attests some testaceans are incapable of motion. Then, what is it that makes him classify the teataceans as animals rather than plants? For it seems that testaceans share more characteristics in common with plants. To this question, Aristotle asnwers in several places that “all animals whatsoever are observed to have the sense of touch,” and that “some classes of animals have all the senses, some only certain of them, others only one, the most indispensable, touch.” Further, in PN he also says sensation is found in all animals, “for by its presence of absence we distinguish between what is and what is not an animal.” In elsewhere in PN, again, he repeatedly states that “a thing need not, though alive, be animal; for plants live without sensation, and it is by sensation that we distinguish animal from what is not animal,” and that “it is called animal because endowed with sensation.” It is then apparent that “it is by sense-perception that an animal differs from those organisms which have only life.” And teataceans possess the sense of touch. It seems then that it is appropriate to classify carnivorous plants as animals rather than plants, for they do seem to react to external objects. But about what stomachs? For Aristotle at one point says that all animals have a stomach. Do carnivorous plants have a stomach? They must, for it would be inconceivable for them not to have a stomach, i.e. a place for concoction, since they do take in undigested food, i.e. flies, in addition to absorbing nutrition from the soil. Sundews or venus flytraps and other carnivorous plants, in fact, seem to form a temporary stomach “with the edges of their leaves curl[ing] inwardly… with the glands of the closely inflected tentacles pouring forth their acid secretion, which dissolves animal matterm afterwards to be absorbed.” Now, carnivorous plants have met the two major requirements for being classified as animal: namely, the possession of sense of touch and the possesion of a stomach. One more thing can be said about how carnivorous plants do not necessarily meet the characteristic pecular to plants, that is, they do not take in food only from the roots, but also from the leaves. Moreover, since these carnivorous plants take in food both from the lower part of their body and from the upper part of their body, they do not seem to have a solid distinction of up and down. This reminds us of a case with molluscs when Aristotle talks of them in IA that it is hard to determine where the movement of molluscs originates, “for they have no distinction of left and right.” If molluscs are animals, why cannot carnivorous plants that seem to have no distinction of up and down be classified as animals? Further, if testaceans that do not move but have only sense of touch can be classified as animals, what prevents carnivorous plants from being classified as animal? Now, this raises another interestion question, for Aristotle says in one place that “taste also is a sort of touch; it is relative to nutriment, which is just tangible body… hence it is that taste also must be a sort of touch, because it is the sense for what is tangible and nutritious,” and in another that “we may say that touch and taste necessarily appertain to all animals.” He also seems to imply that touch and taste are somewhat one. They are similar in that touch and taste are the only senses that receive information without mediation. Further, he makes a claim that “[i]n general, flesh and tongue are related to the organs of touch and taste,” suggesting that the difference between them is only that the latter is senstive to flavour while the former is not. All things considered, it may be that carnivorous plants too could be said to possess not only the sense of touch but also the sense of taste, since they too take in food from the mouth, i.e. leaf, and digest it. In which case, they must be rightly classified as animals as well, since “touch and taste necessarily appaertain to all animals.”

This concludes the discussions of my project to explain, or at least give a conjecture thereof, what place in Aristotle’s biology carnivorous plants can be found. In my exposition, I have discussed 1) how the celestial physics must be studied first in order to study the sublunary physics and the unity between them, 2) what soul is and why the study of plants must be postponed until we have adequately treated the investigation of animals, 3) what are the primary differences of the roles of the nutritive soul in both plants and animals, and finally moved on to postulate some difficulties concerning the borderline cases, that is, 4) whether carnivorous plants should be classified as plants rather than animals. In conclusion, I have argued that it seems plausible that Aristotle would have classified them as animals rather than plants.

Aristotle, Generation of Animals; 731b10, in The Complete Works of Aristotle. Aristotle, however, makes no mention of carnivorous plants in any of his works. This is probably because he did not know about them. My thesis here is that he would have had no choice but categorize them as animals had he known about them, according to his definitions of what animal is.

This is explained by Charles Darwin’s experiments on sundew plants. There, experiments consisted of placing minicule objects on the tentacles of the plant as well as recording an astonishing result that rain drops do not cause the inflection of the tentacles at all. “[I]t is an extraordinary fact that…a human hair, 8/1000 of an inch in length and weighing only 1/78740 of a grain…should induce some change in its cells, exciting them to transmit a motor impulse throughout the whole length of the pedicel… causing this part to bend, and the tentacle to sweep through an angle of above 180 [degrees].” Also “drops of water falling from a height, whether under the form of natural or artificial rain, do not cause the tentacles to move.” Darwin, Darwin, “Chapter II: The Movement of the Tentacles from the Contact of Solid Bodies” in The Works of Charles Darwin Vol. 24 – Insectivorous Plants, 25-27 (NY: New York University Press, 1989)

Aristotle, Generation of Animals; 731b10, in The Complete Works of Aristotle.

Aristotle, Generation of Animals; 761a15-17 and 761b27-28 in The Complete Works of Aristotle.

Aristotle, History of Animals; 546b18 and 590a19, in The Complete Works of Aristotle.

Aristotle, On the Soul; 413b6-8 and 414a3-4, in The Complete Works of Aristotle.

Aristotle, Sense and Sensibilia; 436b11-13, in The Complete Works of Aristotle.

Aristotle, On Youth, Old Age, Life and Death, and Respiration; 467b21-23 and 469a18-19, in The Complete Works of Aristotle.

Aristotle, Generation of Animals; 731b4, in The Complete Works of Aristotle.

Refer to my footnotes 23 and 24 on page 11 in this paper.

Darwin, “Chapter I Drosera Rotundifolia, or the Common Sun-Dew,” in The Works of Charles Darwin Vol. 24 – Insectivorous Plants, 13.

Aristotle, Progression of Animals; 714b8-9, in The Complete Works of Aristotle.

Aristotle, On the Soul; 434b19-20 and Sense and Sensibilia; 436b13-14, in The Complete Works of Aristotle.

Aristotle explicitly says that touch and taste are two different senses at 423a17-21, “That they are several is clear when we consider touching with the tongue; we apprehend at the tongue all tangible qualities as well as flavour. Suppose all the rest of our flesh was sensitive to flavour, we should have identified the sense of taste and the sense of touch; but in fact they are two, for they do not correspond.”

Aristotle, On the Soul; 423b1-3, in The Complete Works of Aristotle.

Aristotle, On the Soul; 423b17, in The Complete Works of Aristotle.

Aristotle, Sense and Sensibilia; 436b13-14, in The Complete Works of Aristotle.