Arber on Theophrastus OCR

8/11/2019 Arber on Theophrastus OCR

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T H E

NATURAL P H I L O S O P H Y

OF PLANT F O R M

Y

A G N E S ARBERM. A. D.Sc. F. R . s . F.L.S.

C A M B R I D G E

AT T H E U N I V E R S I T Y PRESS


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of parts that do so subdivide, for instance, hand is composed of flesh, sinews and bones. In another great zoological work,

Departibus animalium he carries the analysis a stage further back,and traces 'similar parts ' Tex .601oepfl) to certain elementaryforces, 2 or primary substances, 3 from which they are compounded,while the' dissimilar parts ' Tex voo1oepfl) are correspondinglycompounded out of the similar parts. His description of the

. system of the living body is thus that it consists of elements, whichare the material for Tex 601oepfl, which are, in their turn,material for Tex voo1oepfl, which, in the final synthesis, makeup the organism as a whole. The division into similar and dissimilar-or homogeneous and heterogeneous-parts, is roughlyequivalent to the more modern classification into tissues andorgans. In.the Oxford translation of De partibus animalium it wasnoted that this equivalence was incomplete, because Aristotleincluded among homogeneous parts much that we should notcall tissue, e.g. the blood ; 4 but in recent times there has been

. a return to Aristot le in this matter, for blood is now regarded asa liquid tissue. 5

Aristotle held that the plant body was divisible on the sameprinciples as that of animals, but, as i t was -only incidentally thathe touched upon plants , there is more content for us in the writings .

ofhis successor, Theophrastus (S70 B.c. to 285 B.c.), to whom i tseems possible that he may have handed over, deliberately, the

continuation of his work on the botanical aspect of biology.(>- Theophrastus was n


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II. M O R P H O L O G Y OF T H E A R I S TO T E L I A N SCHOOL

teristic features of the botany of the Aristotelian school-a constant reference to animals; in consequence, our botanical language,

from classical times until to-day, has faithfully reflected zoologicalterminology. As examples from Theophrastus we may mention:c r p ~(flesh), for plant pulp; pQ:x s (backbone) for the midrib ofa leaf; Ka:p5ia: (heart) for heart-wood or the pith region; and s(nerve or sinew) for a nerve in the leaf. The theory that the keyto the understanding of plants was to be found in zoology, ledAristotle to suppose that the roots of plants correspond to themouths of animals, since both roots and mouths are members bymeans of which food is absorbed; the plant, on this view, is com

parablewith

an animalstanding on

its head.1

This idea can betraced back to Democritus, 2 while Plato 3 speaks of man as like aplant whose roots are not in the earth, but in the heavens. Thenotion that the root corresponds to the mouth was handed on byBoethius, who, in the sixth century A.D. , wrote of plants, as itwere, thrusting their head into the ground , 4 while, even in thesixteen hundreds, Bacon quotes with approval, Homo est plantainversa. 5 As late as the mid-nineteenth century, a well-knowntext-book 6 sponsored the crudely conceived analogy between root

and mouth. The author writes that many insects supportt h e m ~

selves wholely by suction; and all plants do the same . Hegoes on to explain that plants are provided, not with a singlesucker, like the leech or the flea, but with many . These suckershe describes as taking the form of spongelets at the extreme tipsof the rootlets, which absorb 'carbonised water' .

Theophrastus, with his wider botanical knowledge, tended tobe more cautious than Aristotle about analogies between theanimal and vegetable worlds: he says that w e must not assume

that in all respectsthere

is complete correspondencebetween

plants and animals' ' ;7 but with this reservation, he often turns to

1 Peck, A. L (1937), pp. 370-1 [Depart anim. 1v. x. 686bJ; Hett, W . S (1935),pp. 69 89 [On the Soul 11 i. 412b; II. iv. 416c].

2 Cornford, F. M. (1937), p. 357.s Cornford, F. M. (1937), p. 353 [Timaeus 90J.4 Boethius, A. M. T. S. (1609), bk. II, xi, opp. p. 80; for a revised version of this

translation, see Stewart, H.F. and Rand, E. K. (1918), The Consolation of Philosophypp. 280-1.

5 Bacon, F. (1631), p. 151; this edit ion quoted as the first is not accessible to thewriter.

6 Rennie, J (1849). pp. 88, 92. 7 Hort, A. (1916), vol. 1 pp. 6 7 [1 i 4J.

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THEOPHRASTUS

analogy for help, and he is indeed right in doing so. For humanthought can proceed only by passing from the known to the

unknown, on the assumption that there is some degree of real analogy between the two. 1 It has been a certain handicap to the

study of plants, that, owing to man s primary interest in theanimal world, to which he belongs, his attention was naturallyfirst focused upon this, and plants were thus left to be interpretedsubsequently through zoological comparisons; the reverseprocess might at times have been more illuminating.

The botanical work of Theophrastus is of such importance, asthe basis on which even to-day we s till build, that it is necessaryto consider it in some detail, at least as regards those aspectswhich bear definitely upon morphology. Our knowledge of hisoutput is derived from two books, De causis plantarum (Tiepl q>vTwvah1wv), and De historia plantarum (TTEpi q VTWVicrTopio:). It hasbeen suggested 2 on internal evidence that De causis is relativelyearly, while the Historia in which the vocabulary shows greaterrichness, precision, and specialisation, represents a group of laterworks. The influence of Aristotle is conspicuous in De causiswhile the Historia shows more independence. 3 Both treatiseshave some of the characteristics of lecture notes. 4 The fact thatneither of them is a fully integrated individual work, representing

a final written version of the author s views, does not add to theease of interpretation; but, even so, a gre(:lt part of their contentis lucid and of profound interest.

The Historia opens with an account of the general scope ofbotany. Theophrastus tells us that we must take into consideration: ( 1) the parts of plants; ( 2) their qualities; ( S) the way inwhich their life originates; and ( 4) the course which their lifefollows. He adds that behaviour and activities, such as we witnessin animals, are not to be found in plants. This classification, whichis remarkable for its comprehensiveness, might be restated in

modern terms as representing the division into ( 1) morphology;2) physiology and biochemistry; s) the study of reproduction

1 Cf. Hort, A. (1916), vol. 1, pp. 18, 19 [1. ii. 4J; on analogy in the history ofscience, see Arber, A. (1946b).

2 Stromberg, R (1937), p. 136; for a careful chronological study of the botany ofTheophrastus, see Senn, G. (1933).

8 Senn, G. (1930), p. 113.4 Vorlesungsmanuskripten , Stromberg, R. (1937), pp. 69-70.

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and development; 4 the study of life-histories. Theophrastusgoes on to say that, of these subjects, that dealing with the partsof plants morphology) presents the greatest difficulty. Writing,as he did, more than 2000 years ago, he was naturally not ina position to make a critical comparison between the obstacles tobe overcome in these various regions of research, but his appreciation of the complexity of morphology indicates that this was thefield into which he had the clearest insight; it is indeed the field inwhich his influence has been most lasting, while that of Aristotlehas been more deeply felt in the study of behaviour, and of'purposeful' structure. 1 The difference of emphasis in the work ofthese two pioneers possibly represents a natural cleavage betweenthe standpoint of the botanist and zoologist-the botanist inclining to the consideration of form, and the zoologist to that offunction.

W e have already mentioned Aristotle's realisation of theexistence in the animal body of homogeneous parts tissues),which are the components of heterogeneous parts organs).Among plants, correspondingly, he recognised organs, but hesays that they are of a simpler type; he instances leaf and seedvessel.2 Theophrastus carries the analysis to a further point, andclassifies plant organs under two categories: th main parts suchas root, stem, bough, and twig; and the annual parts such asflower, leaf, fruit, and 'new shoot'. On comparing the parts ofplants with those of animals, he is struck by the impermanence ofthe plant members of the second category, and with the fact thattrees make fresh shoots every year, so that the number of partsis indeterminate and continually changing, whereas in the higheranimals the number of organs is fixed and definite. He evidentlyfeels that this is a divergence which must be accepted as such,without trying to force our conception of the plant into the framework derived from zoology. He holds that i t is waste of timeto take great pains to make comparisons where that is impossible ;3 this may seem to be a glimpse of the obvious, but in those

days the overstrained animal analogy had a stranglehold whichit is hard now to realise.

1 Cf. Thompson, D'Arcy W. 1913).2 Hett, W. S 1935), p. 9 [On th Soul 11. i 412bJ.3 Hort, A. 1916), vol. 1, pp. 6 7 [1 i 4J.

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Arber on Theophrastus OCR