Notwithstanding its title, this is not a book about plants, dedicated to the natural condition of plants within the framework of any interests of ancient Stoics for botany as a disciplinary area. It is a book on Stoic ethics, which analyses the key notion of kathēkon to show that ethics has a natural foundation and there is a close link between ethics and physics (pp. 17–19). The plants in the title are therefore only representative of the level of nature to which the notion of kathēkon extends in Stoic ethics, while their own constitution, formation and nature are taken for granted, not explained. This is not a marginal issue. For, in the view of the Stoics plants are inanimate natures because they do not have in themselves the principle of movement, and for this reason they differ both from animals, enjoying sense perception, and from human beings, endowed with senses and reason; it is not the soul that controls plants, but nature directly (SVF 2, 708; 710).

In the course of his enquiry L. correctly distinguishes at length the different meanings of kathēkon at different levels of living beings (pp. 33; 130–6; 140–6). Perhaps it would have been worthwhile to make explicit that the kathēkon is not linked to the possession of psychē at all levels and verify whether or not the definition of the notion varies in the passage from the animate level to the inanimate one. The soul as a reference point in the organisation of living beings in the scala naturae is a relevant absence in the analysis.

A couple of preliminary remarks inform the reader that the research is (a) limited to the ancient Stoics, of whose positions, however, only a sketch will be provided, and (b) based on a selection of the sources by which the doctrine is reported (pp. 17; 21–31). I suspect that these two remarks are related and in particular that the former depends on the choice of selected sources in the latter. Limiting the analysis to the ancient Stoa is a legitimate and partly acceptable operation; in this way the developments in the notion of kathēkon within the school by later Stoics such as Panaetius are not explored, but it is nevertheless important that the context in which the doctrine originally took shape is examined. What instead appears questionable is the selection of sources. Preference is given to the doxographic accounts of Diogenes Laertius and Stobaeus, while Cicero's testimony is rejected on the grounds that it is not authentic testimony of orthodox Stoic ethics. On the contrary, the doxographers’ versions, despite their scholastic exposition, are regarded as providing a more reliable picture because of their systematic and neutral character (pp. 23–5; 29). But, without detracting from the importance of doxographic testimonies, often unique sources of information for us, the arguments for Cicero's exclusion appear a little prejudicial and not very convincing. Since he did not adhere to any philosophical sect (he was not a school philosopher), a certain degree of neutrality should be expected; indeed, his sympathies for the New Academy required him to examine the reasons and discuss them without misrepresenting anything so as not to compromise the final verdict on the theory. I am also not sure that we can speak of an orthodox Stoic ethics as a single and unmodifiable body of doctrines, even assuming that the category of orthodoxy is applicable to the ancient world. In fact, Cicero's exclusion seems to be not well founded. For, while in his exposition (Cic. Fin. 3.20–9) the scope of the kathēkon is restricted to human beings, in the exposition of Diogenes Laertius (7.107–10) particularly the scope is extended to animals and plants, and the doctrine's foundation is attributed at the same time to Zeno, then to the early Stoics. The discrepancy is therefore removed, not discussed, and the analysis is in practice confined to a single piece of evidence, although of special interest.

The core of the question is reached when L. proceeds to define the meaning to be given to the notion of kathēkon. From here this part of the book (Chapters 3–5) shows the greatest originality (p. 67), and it constitutes the volume's central point. This section is largely conjectural, in which a kind of circumstantial process is developed, with somewhat forced conclusions. In L.'s opinion the current translations of kathēkon such as ‘Pflicht’, ‘duty’ or ‘fitness of behaviour’ refer only to the human sphere, but are inadequate to cover animals and plants (pp. 38–46). He therefore goes in search of a rendering of the term that respects its connection with prattein and praxis, hence with action, but can also be applied to non-rational beings, and he believes that he can identify it in the meaning of activity or absolving certain functions that praxis sometimes assumes in Aristotle's biological writings (pp. 65–73). Although the evidence that the early Stoics read Aristotle's works is tenuous (pp. 66–7), L. believes he can argue that, precisely on the basis of cornerstones of his biology, the Stoics could justify by this biological-naturalistic interpretation of praxis the attribution of kathēkonta even to non-rational beings such as plants (pp. 67–70; 129). This is even more so because Aristotle frames the study of the activities of all living beings qua living beings as activities facing an end, that is, in a teleological perspective (pp. 70–3; 100–4). The human level would therefore be the only case where the kathēkon would have a strictly rational foundation; the criterion in this case would be the being in which the reason is perfect, namely the Wise as ‘“Exeget” des Naturgesetzes’ (pp. 172–5).

There are, however, some difficulties. Obviously, the Stoic kathēkonta of plants should be in Aristotelian terms nutrition and reproduction, that is, the functions that in De an. 2.4, 415a23–b7 Aristotle attributes to the first soul (pp. 79–85). The problem is that for the Stoics neither did plants have soul, nor did they include in their definition of the soul the Aristotelian nutritive soul in both its strictly related functions, nutritive and generative. Therefore, the Aristotelian nutritive soul could not be the principle of self-movement by which plants can perform their own functions. Nor does it seem that Aristotle's natural teleology can be adapted to the cosmo-teleology of the Stoics. According to L. (p. 74) global teleology in Aristotle could not be excluded, considering that the principle is universally applied by him to all species of living beings and extended to celestial bodies as well. But Aristotle's nature, unlike the Stoics’, is not an intelligent way of generating or animated by a divine logos, nor even an infallible technique such as Zeno himself conceived it, when he defined nature as ‘ignis artificiosus that proceeds methodically to generation’ (SVF 1, 171). Hence it is one thing to say with Aristotle that nutrition and reproduction are operations of the nature of plants and ends that are carried out according to a conditional necessity (not always and invariably). It is another thing to say with the Stoics that nutrition and reproduction are actions that plants carry out not by choice or impulse but adapting to what for them was projected by the divine logos and to the decrees of the law of nature.

The complexity of the addressed themes perhaps required more conceptual insights into biological and ethical areas; and the discussion of more up-to-date bibliographical references to studies on plants in antiquity and on Stoic ethics could have given the analysis a less schematic and more problem-focused character, especially suitable when dealing with demanding and controversial issues such as those dealt with here.