Illustrations of Indian Botany, Vol. 2/Granateae

by Robert Wight

LXIV.—GRANATEAE.

The most eminent Botanists of the present day are divided in opinion as to the propriety of considering this a distinct order, or merely a section of Myrtaceae. Don. DeCandolle, and Martins, view it as a distinct order. Lindley, Arnott and Meisner, take the opposite side of the question. At the time of preparing the accompanying plate and long after, when writing my account of Myrtaceae, I also adopted the latter view—circumstances having occurred to delay the publication of that article I have been enabled to reconsider the subject and review afresh the arguments on both sides, carefully examining the structure of the ovary and fruit as I went along. The result has led to the conviction that this is really a distinct order. I should scarcely I think have come to this conclusion had I not previously ascertained the possibility of carpels having their position reversed in the ovary, because until I did ascertain this, I could not understand or explain, to my own satisfaction, the appearances which sections of this ovary presents and preferred regaining silent to giving an opinion which I felt myself unable to support. Having at length been enabled to make up my own mind on the subject, I. shall here explain my views and contrast them with those of my predecessors who have written on the subject. As the main object of the strictly Botanical portion of this work is to explain the principles of the science, I trust I shall be excused for considering somewhat at large a question on which the sentiments of so many eminent Botanists are divided. I regret being unable to quote professor Endlicher's opinion, not having yet received the part of his genera Plantarum containing this order. The following extracts will place before the reader both sides of the question which wholly rests on the views each author takes of the structure of the fruit. Don, the original proposer of the order, and DeCandolle describe it thus.

"Ovary cohering to the tube of the calyx free at the apex many celled. Berry apple-shaped crowned with the contracted limb of the calyx; rind thick, covered exteriorly with a redish smooth cuticle with shining points, spongy within; the berry when ripe bursting irregularly. Placenta resembling the substance of the rind but more fleshy and succulent, completely filling the berry, excavated into numerous unequal many seeded cells. No true partitions, but spurious ones, arising from the substance of the placenta, of variable thickness and very fragile"^[1] or as explained by himself in English " a fleshy receptacle formed by the tube of the calyx into a unilocular berry filled with a spongy placenta, which is hollowed out into a number of irregular cells in which the seeds are placed, the dissepiments being nothing more than thin portions of the placenta. Don. Edin. New Phi. Jour. 1826.

"Fruit large, spherical, crowned by the limb of the calyx, indehiscent; the fruit is the tube of the calyx divided horizontally into two chambers or parts, the upper division 5-9 celled, the lower division 3 celled; the dissepiments membranous separating the cells; the placentas of the upper part of the fruit fleshy, reaching from the parietes to the centre; those of the lower divisions progressing irregularly from the bottom of the fruit." D.C. prod. — Pg. 3.

On the opposite side Lindley examines the question at great length and is followed by Arnott, who gives a more brief but I think better exposition of the argument on this side than his leader. 1 subjoin both in full.

"The fruit of the Pomegranate is described by Gartner and DeCandolle as being divided into two unequal divisions by a horizontal diaphragm, the upper half of which consists of from 5 to 9 cells, and the lower of 3; the cells of both being separated by membranous dissepiments; the placentæ of the upper half proceeding from the back to the centre, and of the lower irregularly from their bottom; and by Mr. Don as a fleshy receptacle formed by the tube of the calyx into a unilocular berry, filled with a spongy placenta, which is hollowed out into a number of irregular cells. In fact, if a Pomegranate is examined, it will be found to agree more or less perfectly with both these descriptions. But it is clear that a fruit as thus described, is at variance with all the known laws upon which compound fruits are formed. Nothing, however, is more common than that the primitive construction of fruits is obscured by the additions, or suppressions, or alterations, which its parts undergo during their progress to maturity. Hence it is always desirable to obtain a clear idea of the structure of the ovarium of all fruits which do not obviously agree with the ordinary laws of carpological composition. Now, a section of the ovarium of the Pomegranate in various directions, if made about the time of the expansion of the flowers before impregnation takes place, shews that it is in fact composed of two rows of carpella, of which three or four surround the axis, and are placed in the bottom of the tube of the calyx, and a number, varying from five to ten, surround these, and adhere to the upper part of the tube of the calyx. The placenta of these carpella contract an irregular kind of adhesion with the back and front of their cells, and thus give the position ultimately acquired by the seeds that anomalous appearance which it assumes in the ripe fruit. If this view of the structure of the Pomegranate be correct, its peculiarity consists in this, that, in an order the carpella of which occupy but a single row around the axis, it possesses carpella in two rows, the one placed above the other, in consequence of the contraction of the tube of the calyx, from which they arise. Now, there are ninny instances of a similar anomaly among genera of the same order, and they exist even among species of the same genus. Examples of the latter are, Nicotiana multivalvis and Nolana paradoxa, and of the former Malope among Malvaceae; polycarpous Ranunculaceae as compared with Nigella, and polycarpous Rosaceae as compared with Spiraea. In Prunus I have seen a monstrous flower producing^ number of carpella around the central one, and also in consequence of the situation, upon the calyx above it; and., finally, in the Revue Encyclopedique (43-762), a permanent variety of the apple is described, which is exactly to Pomaceae what Punica is to Myrtaceae. This plant has regularly 14 styles and 14 cells, arranged in two horizontal parallel planes, namely, 5 in the middle, and 9 on the outside, smaller and nearer the top ; a circumstance which is evidently to be explained by the presence of an outer series of carpella, and not upon the extravagant hypothesis of M. Fillette de Clermont, who fancies that it is due to the cohesion of 3 flowers." — Lindley's Natural System of Botany.

"This genus only differs from the other Myrtaceae by having two verticels of carpels developed instead of one, and perhaps in a truly wild state the upper or adventitious one may occasionally disappear. The inner series (or those at the bottom of the fruit) have their placentæ in the axis ; but the outer series, forced to the top of the fruit by the contraction of the mouth of the tube of the calyx, having their placentæ in the ovary at the back of the inner carpels, exhibit them in the ripe fruit in a horizontal position on the upper surface of the lower cells." — Arnott Encyclop. Brit. Ed. 7, et Prod. Fl. peninsula I Pg. 327.

Premising that the whole controversy turns on these questions, 1st, what is the true structure of a Pomegranate? and 2d, whether the difference between it and Myrtus is sufficient to separate these genera as types of distinct orders ?

I shall now proceed to examine these conflicting statements and endeavour to ascertain on which side the balance preponderates and whether indeed, there is not room for an explanation different from any of these yet proposed.

Mr. Don's description of this fruit on the strength of which he first proposed to remove this genus from Myrtaceae, the order with which it was previously associated, as a distinct family appears to me most unphilosophical and altogether, untenable. He, as I understand, considers the fruit a one celled receptacle the centre of which is filled with a spongy placenta, round the surface of which there are a number of irregular cells occupied by clusters of ovules: but he does not tell us how the central placenta got there neither does he account for the ovules being attached to the parietes of the cell and not to the central placentæ.

His whole description in fact proves that it had been drawn up from inadequate examination and that he, at the very time he is accusing all authors of overlooking the real structure of this fruit, totally misapprehends it himself, as we shall by and by see.

DeCandolle gives a more correct description of it when he says that it consists of two chambers, the under 3-celled, the upper from 5 to 9-celled, with the placentas of the upper cells reaching from the parietes to the centre while those of the lower division proceed irregularly from the bottom of the fruit. He does not however assign this peculiar structure as his principal reason for viewing the order as distinct from Myrtaceae, but has recourse to others in my estimation of minor importance.

Lindley conceives that there are two rows of carpels, three or four of which surround the axis at the bottom, while the remainder surround these and occupying the upper part of the fruit adhere to that part of the tube of the calyx. The placentas of these upper carpels he conceives contract an irregular kind of adhesion with the back and front of their cells. The meaning of this is far from being: clear to me, but if it means that he considers the placentas of the upper as well as the lower row to proceed from the axis towards the circumference to which last they contract accidental adhesions, then he takes an erroneous view and if the examples quoted in illustration support this view, they are not in point as regards the structure of Punica.

Mr. Arnott like Lindley views the fruit as consisting of two rows of carpels, an outer and inner, the former of which he thinks may be adventitious. To understand his theory we must first suppose the tube of the calyx spread out as a flat surface and covered with two circles of carpels, the inner next, the axis and the outer occupying a larger circle beyond. That the margin of the calyx then contracts so as to turn the outer series over the inner. According to this supposition, the attachment or base of the placentas of the outer series should be in the circumference and the apex in the centre, while that of the inner should be in the opposite direction, that is, have the base in the centre and the apex towards the circumference, an explanation which is in accordance with what we find, except in so far as it does not account for the horizontal partition between the two series, nor can I exactly understand on what ground we are warranted in assuming that the outer series is adventitious and the result of cultivation, as it has every where been found so constant in all circumstances. But be that as it may. this theory certainly accounts for the crossing of the placentas in the two rows, which we so invariably find, whether correctly or not cannot be determined until we get fruit with a single row of carpels, which has not yet been found. These explanations, which I venture to propose, of rather obscure descriptions did not occur to myself until after I had formed a new theory of my own, the result of a very careful examination of the ovary in all its stages from the earliest, up to the period of impregnation. At these early stages when the whole flower has not yet attained half an inch in length probably a fortnight or more before expansion I invariably find two rows of carpels, one inferior, of 4 or 5 and one superior of 5-6 or more. In the lower series the placentas are ranged round the axis with their base in the centre and the apex, which is free, towards the circumference. In the upper the attachment, or base of the placentas, is in the circumference and the apex, also at first free, directed towards the centre. Between the two rows a diaphragm is always interposed. The apex of the upper placentas is occasionally, afterwards, prolonged and contracts adhesions to the axis.

In the accompanying figures I have attempted to represent these views. As the fruit advances in size considerable derangement of this structure progressively occurs which is apt to mask and confuse the appearances now described.

Having previously ascertained the occasional existence of inversion in the position of carpels, my first idea was that such an inversion took place in the upper row. This view, which, equally with the preceding, accounts for the crossing of the placentas I feel inclined to adhere to, though I confess not without some hesitation, because it implies a complexity of arrangement rarely met with in tire inimitably simple and beautiful operations of nature, but I think it as difficult to imagine the nearly equally complex and inconceivable operation of the folding in of one set of carpels over the other, which the explanation of Drs. Lindley and Arnott demand, while my explanation has the advantage of at the same time accounting for the double chamber which the ovary presents from its earliest stages, and renders unnecessary the doctrine of an adventitious verticel of carpels which for the present is mere assumption.

With these explanations I leave the question of structure to consider the one pending on its determination, viz. whether or not Granteae ought to be preserved as a distinct order or be reunited to Myrtaceae?

On this point so far as the unvarying evidence derived from cultivated plants is entitled to carry weight on a disputed point — and which I presume it must do until we find that evidence invalidated by the examination of others growing in a truly wild state — we must unquestionably, I conceive, adopt the views of those who urge the separation, because, the complex structure, above described, being constant here and unknown among true Myrtaceae, we have no right, in the total absence of direct confirmatory evidence, to assume that a part is adventitious, merely because it is at variance with our ideas of what should be, especially while we have in addition, differences in habit, in the formation of the seed (the cotyledons are foliaceous and spirally convolute) and in their pulpy envelope still further to confirm the correctness of these views.

In coming to this conclusion I do so mainly on the evidence I have myself adduced, attaching no value to the opinion of Mr. Don, which, being founded, according to his own showing, on most erroneous views of the structure of the fruit does not merit much consideration.

To the views of DeCandolle more importance must necessarily be attached, as the reasons he assigns are more satisfactory, though I do not think he has awarded sufficient value to the very peculiar " economy of the fruit" while he has laid too much stress on others of much less note, such as the want of pellucid dots, the absence of the marginal nerve of the leaves and the pulpy covering of the seed ; thereby, throwing into the shade the true essential character of the order, which unquestionably is the double row of carpels, with the upper placentas parietal and crossing the lower axillary ones, which, if I have rightly accounted for, constitute this a truly curious and unique fruit.

Affinities.}} According to the explanation now given, the affinities of this order remain to be determined, no known order presenting a similar combination of structure. But adopting the arrangement of Jussieu and DeCandolle, the one followed with some slight modifications in this work, we can scarcely find a more appropriate station for it than the one it now occupies, though but remotely allied to the orders among which it is placed. GEOGRAPHICAL DISTRIBUTION. Found widely distributed over Asia but every where cultivated. Arabia is however supposed to be its native country.}}

MEDICAL PROPERTIES. For these see Myrtaceae the order under which I at first included this genus.

EXPLANATION OF PLATE 97.

1. Punica granatum, flowering branch—natural size.

2. Flower and ovary cut vertically.

3. Ovary cut transversely, section near the apex of the ovary; apparently the section seen and described by Don.

4. Stamens.

5. A young fruit cut transversely, showing the parietal attachment of the upper row of carpels.

6. A seed covered with pulp.

7. The same cut transversely.

8. The same more highly magnified, showing the spirally convolute cotyledons.

9. A longitudinal section of the seed showing the embryo in situ.

10. Cotyledons unrolled—all more or less magnified.

For further dissections of the ovary of this plant see plate 97.

SUBORD. GRANATEÆ. MYRTACEÆ. 97/1010

PUNICA GRANATUM (LINN.)

1. Ovarium tubo calycis accretum, apice liberum, multiloculare * * * Bacca pomiformis, limbo tubuloso dentato calycino, nunc contracto, coronata : cortex crassissimus, extus cuticula lævi rubicunda punctala lucida vestitus, intus spongioso-carnosus, albus, dein, matura bacca, fissura irregulariter rumpens — Placenta cortici baccɶ substantia simillima, at magis carnosa et succulenta, baccam omnino replens, in loculis numerosis polyspermis inaequalibue reticulatim atque interrupte excavata. Dissepimenta vera nulla: spuria tamen adsunt, quæ e substantia placentæ orta, valde sunt fragilia, et crassitie varia." (Don. 1. c.)