Transactions of the Linnean Society of London/Volume 12/Some Observations on the natural Family of Plants called Compositæ

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Chapter 11: Some Observations on the natural Family of Plants called Compositæ by Robert Brown

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2594717Transactions of the Linnean Society of London, Volume 12 — Chapter 11: Some Observations on the natural Family of Plants called CompositæRobert Brown

XI. Some Observations on the natural Family of Plants called Compositæ. By Robert Brown, Esq. F.R.S. Libr. L.S.

Read Feb. 6 and 20, 1816.

The class Syngenesia of the Linnean artificial system, as at present limited, constitutes a family strictly natural, and by far the most extensive in the vegetable kingdom. It is also, with the exception of Grasses only, the most generally diffused, and is almost equally remarkable with that order, for the great apparent uniformity in the structure of its essential parts of fructification.

This class of plants, for which I retain the established name Compositæ, in preference to any of those recently proposed, has lately become the subject of a minute and accurate examination by Mons. Henri Cassini; two of whose Memoirs on the Style and Stamina of the class, already published in the Journal de Physique^[1], are in my opinion models for botanical investigation.

A few years before the publication of M. Cassini's Memoirs on Compositæ I was induced to examine a considerable part of this extensive family, chiefly with a view to the more accurate determination of the New Holland plants belonging to it.

My principal object in the present paper is to communicate such general observations, the results of this investigation, as either have not yet been published by M. Cassini, or respecting which I consider myself to have anticipated that author in my General Remarks on the Botany of New Holland, appended to Captain Flinders's Voyage to Terra Australis.

To these observations I shall add some remarks on certain genera of Compositæ, which occur repeatedly under different names in late systematic works, and whose structure and limits appear to be imperfectly understood.

My first observation relates to the peculiar disposition of the nerves or vessels of the corolla of this family of plants.

In the essay already mentioned, which appeared early in the summer of 1814, I have noticed this peculiarity in the following terms:

"The whole of Compositæ agree in two remarkable points of structure of their corolla; which, taken together at least, materially assist in determining the limits of the class. The first of these is its valvular æstivation; this however it has in common with several other families. The second I believe to be peculiar to the class, and hitherto unnoticed. It consists in the disposition of its fasciculi of vessels or nerves; these, which at their origin are generally equal in number to the divisions of the corolla, instead of being placed opposite to these divisions, and passing through their axes as in other plants, alternate with them; each of the vessels at the top of the tube dividing into two equal branches, running parallel to and near the margins of the corresponding laciniæ, within whose apices they unite. These, as they exist in the whole class and are in great part of it the only vessels observable, may be called primary. In several genera, however, other vessels occur, alternating with the primary, and occupying the axes of the laciniæ: in some cases these secondary vessels being most distinctly visible in the laciniæ, and becoming gradually fainter as they descend the tube, might be regarded as recurrent; originating from the united apices of the primary branches; but in other cases, where they are equally distinct at the base of the tube, this supposition cannot be admitted. A monopetalous corolla not splitting at the base is necessarily connected with this structure, which seems also peculiarly well adapted to the dense inflorescence of Compositæ; the vessels of the corolla and stamina being united and so disposed as to be least liable to suffer by pressure."

At the date of this publication I certainly had no knowledge of any similar observations having been previously made: but I now see in M. Cuvier's account of the proceedings of the Institute of France for 1815, that M. Cassini is considered as having anticipated me on this subject, and as he says in "termes non équivoques." What these terms are, appears by a letter I have received from M. Cassini himself, in which he states his claim to rest on the following passage:

"Chaque fleur hermaphrodite ou male contient cinq étamines, correspondant aux cinq nervures de la Corolle et par conséquent alternes avec ses lobes."

This passage occurs in a Memoir on the Stamina of Compositæ, which was read to the Institute of France in July 1813, and first appeared with the substance of that Memoir in the Journal de Physique, said to be for April 1814; but the actual date of the publication of which I have reason to believe was somewhat later, and very nearly corresponding with that at which M. de Jussieu was in possession of a copy of my essay containing the observations already quoted. I conclude it is not supposed I could have been acquainted with the passage in the original memoir, unless the report usually made on memoirs read to the Institute should have been printed, and should have actually noticed this passage or the discovery it is now said to contain.

But independently of the near equality of dates, I cannot consider my observations as either wholly or even in any considerable degree anticipated by the passage in question. My observations notice not only the disposition of the five vessels in the tube of the corolla, but their ramification in the laciniæ, by no means a necessary consequence of that disposition; they notice also the existence, in several genera of Compositæ, of five vessels alternating with those, and which I considered secondary in this order, though they occupy the place of the primary vessels in other families: and it is this inverted disposition, indicated in the greater part of the class by the primary being the only vessels existing, which I have considered as of material importance in determining the limits of Compositæ, though by no means as affording an essential practical character for the whole class.

In the passage quoted from M. Cassini (the only one I can find relative to the subject in the memoir in which it occurs), the existence of five nerves or vessels in the tube of the corolla, alternating with its laciniæ, is stated, but their division and disposition in the laciniae are not noticed; it is at the same time to be inferred from the terms of the passage, that no other vessels exist in the tube of the corolla: and it is equally evident that, so far from announcing this disposition of vessels as a discovery, or peculiar to the order, the author rather considers it either as a fact already known, or as the usual structure. That M. Cassini was not then aware of the importance of the fact which he had imperfectly stated, appears likewise from his having, many months after his memoir was read, and at a time when he says he had finished his analysis of the corolla, proposed a name for the class, taken from a supposed peculiarity in the structure of the filament, a name which he is now inclined to abandon for one derived from the disposition of vessels in the corolla.

Since my attention has been again turned to the subject, I have endeavoured to collect all that has been observed on the nerves or vessels of the corolla of Compositæ. a brief account of which may be not altogether without interest.

The earliest notice I have been able to find is contained in a passage (in page 170) of Grew's Anatomy of Plants, where, in speaking of syngenesious flosculi, he says, "they are frequently ridged, or as it were hem'd like the edge of a band." And his figure of a magnified floret of the common Marigold, in tab. 61, gives a tolerable idea of the marginal vessels of its laciniæ. Grew however takes no notice of the trunks from which these branches arise, either in his text or plates.

Van Berkhey, in his Dissertation on Compositæ, published at Leyden in 1760, though he makes no mention of the nerves of the corolla in his text, yet in all the magnified figures he has given both of ligulate and tubular florets, correctly represents the trunks of the primary vessels, without however noticing their ramification in the laciniæ. I am anticipated therefore by this author's figures exactly in the same degree as by the passage contained in M. Cassini's second memoir.

The accurate Schmidel, in the few Compositæ which occur in his Icones, has correctly represented the trunks of the primary vessels, but has equally omitted their ramifications.

In the Analysis Florum of Batsch, a work published in 1790, the object of which was to give an idea of the structure of the natural families of plants, by a minute description and magnified figures of one or more species selected from each. Coreopsis tripteris occurs; and although the vessels of its tubular floret are very indistinctly figured, yet both their trunks and branches are correctly described. The same author however, who in 1802 established an ingenious work on the natural families of plants^[2], takes no notice of the vessels of the corolla in the character of Compositæ which he has there proposed.

In the figures of syngenesious plants given by Schkuhr^[3], whereever the ligulæ of Cichoraceæ are magnified, the trunks of the nerves are correctly represented ending in the sinuses; unless in one plate containing Lactuca virosa and Sonchus sibericus, in both of which the vessels are made to pass through the axes of the teeth; but in no case are the marginal branches noticed. It is singular that this generally accurate author, in the many magnified figures he has given of tubular florets, has only in two cases represented the trunks of their vessels, namely in Echinops Ritro, where they are correctly placed, and in Silphium trifoliatum, where, though only five vessels are visible, they are erroneously made to pass through the axes of the laciniæ.

The only remaining author that notices these vessels is M. Mirbel, who in the second part of his valuable Elémens de Physiologic Végétale et de Botanique, published in 1815, introduces into his character of Compositæ the fact of the laciniæ of the corolla being furnished with marginal nerves. This observation, if not original, the author may have adopted either from my essay already quoted, of which he was in possession soon after its publication, or from M. Cassini's third memoir, which was read to the Institute of France six months after that essay appeared: but he could not have derived it from the passage in that author's second memoir, on which he rests his claim; no notice being there taken of the disposition of vessels in the laciniæ.

In M. Cassini's memoir expressly on the Corolla of Compositæ, which was read to the Institute of France in December 1814, and of which an abstract, by the author himself, is given in a late number of the Nouveau Bulletin des Sciences, the disposition of vessels in the corolla is expressed in the following terms:

"Chacun des cinq petales dont se compose la corolle est muni de deux nervures très simples qui le bordent d'un bout à l'autre des deux côtés, et confluent par conséquent au sommet."

On this statement I have several remarks to offer. And first, I object to its hypothetical language. Whatever opinion may be formed of the theory here adopted by the author, namely, that every monopetalous corolla is in reality composed of several confluent petals; a theory first proposed by Linneus himself in his Prolepsis Plantarum, and ably supported on different grounds by Mons. Decandolle in his excellent Théorie Elémentaire de la Botanique; I can see no advantage in adopting its language in stating a fact of this kind, especially if proposed as a practical character.

For my own part, I consider this opinion as correct in the sense in which it was held by Linneus, without, however, connecting with it the ingenious hypothesis of M. Decandolle, namely, that petals are only modified stamina. It remains to be seen on what ground M. Cassini has adopted this theory, as proposed by M. Decandolle, for Compositæ, the only family which seems to present a very important objection to it, in having its principal, and in the greater part of the order its only, vessels occupying the lines of junction of the supposed united petals.

To adapt this disposition of vessels to the theory, M. Cassini is obliged to subdivide their apparently simple trunks; a division, however, which may be regarded as entirely hypothetical. From the observations I have made on the subject, I have no doubt that these trunks are equally simple with the secondary nerves when present, or with the primary in other families. I find them to consist of two kinds of vessels, the spiral and ligneous. Of the spiral vessels there arc generally several in the cord: in Helianthus multiflorus, however, I have not been able to find more than one, either in the trunk of the nerve above the insertion of stamina, or in the branches of the laciniæ. It will be of some interest to verify this fact (which I by no means give with absolute confidence), both on account of the apparently formidable objection it presents to the theory in question, and also that, in following it up by an examination of the point of division, a clearer idea may be obtained of the ramification of spiral vessels than has hitherto been given.

My second objection to M. Cassini's account is, that he describes the nerves as marginal through their whole length. I have formerly, in the passage already quoted, stated them to be parallel and approximated to the margins of the laciniæ. Perhaps in no instance can the branches be considered as strictly marginal; in many cases they are manifestly distinct from the margins, and in the genus Hymenopappus are further removed from them than from the axis of the laciniæ. In H. scabiosæus there is also an evident inequality of the two branches in each laciniæ, the stronger extending nearly to the apex, while the weaker either entirely disappears before it reaches the stronger, or unites with it considerably below its termination. In H. tenuifolius this irregularity is still greater; one branch being not unfrequently altogether wanting, and even the remaining branch considerably weakened: where this happens a secondary vessel is always produced, though very few flosculi are furnished with five complete middle nerves.

It may seem rather paradoxical to select Euphorbia as an example of the same relation; this genus being considered by Linneus, and the greater part of the botanists who have adopted his system, as having a dodecandrous hermaphrodite flower. We have already, however, I believee sufficient evidence that this supposed hermaphrodite flower is in reality formed of several monandrous male flowers surrounding a single female^[4].

In conformity with this view of its composition, and with the relation above attempted to be established, the development of the pistillum precedes that of the stamina in many species of the genus.

It is more difficult to determine whether this order of expansion and relative position of sexes in Euphorbia be in conformity with the general rule, or an exception to it. For its faciculus of flowers may be considered as analogous either to the simple spike, and. consequently having an inverted order of expansion, as in Allium descendens, and certain species of Grevillea and Anadenia: or it may be assimilated to the compound spike, as in several species of the genus the male flowers appear to be separated into fasciculi; Page:Transactions of the Linnean Society of London, Volume 12.djvu/128 Page:Transactions of the Linnean Society of London, Volume 12.djvu/129 Page:Transactions of the Linnean Society of London, Volume 12.djvu/130 Page:Transactions of the Linnean Society of London, Volume 12.djvu/131 Page:Transactions of the Linnean Society of London, Volume 12.djvu/132 Page:Transactions of the Linnean Society of London, Volume 12.djvu/133 Cook's second voyage, and now in the library of Sir Joseph Banks, there is a figure of this plant, from which it appears that he originally referred it to Staehelina; a proof that he had not at that time very carefully examined it. It is not improbable therefore that he afterwards proposed it as a distinct genus, belonging to Polygamia segregata, from finding that this had been already done by Solander, whose name (Cartodium), however, he did not think it necessary to adopt, and with whose generic character he probably was not acquainted. In his own he very erroneously states that there is no partial involucrum, and hence perhaps M. Labillardiere entirely overlooked Craspedia when he established his Richea from a nearly related species of the same genus. That such is the case I have long since briefly noticed*, and have ascertained by a comparison of the specimen of Craspedia uniflora in George Forster's Herbarium with Richea glauca of Labillardiere, and other species of the same genus which I have observed in New Holland.

M. Labillardiere's character of Richea is essentially correct. It is well to remark, however, that his general involucrum is formed of the bracteae subtending and in equal number with the outer partial capitula; and that the general receptacle has no other paleae than the analogous bracteae of the inner capitula. It is the more necessary to take this view of the structure, as I have found in New Holland a nearly related genus (Calocephalus), which differs from Craspedia and Richea in the want of these bracteae, as well as in the partial receptacles being without paleae;, and in the rays of the pappus being plumose only in the upper part. I have also another genus of this tribe (Leucophyta) from the same country, differing from Calocephalus in having a general involucrum consisting of a few short bracteae, in the squamae of its partial involucra being concave and bearded at top, and in the rays

In Prodr. Flor. Nov. Holl. p. 555.

of of its pappus being plumose through their whole length, as in Craspedia, from which it is distinguished by the want of paleae on the partial receptacles, and very remarkably in habit.

I have selected the foregoing genera as having been either published under different names, or, as it appears to me, unnecessarily subdivided. In this extensive class it would not be difficult to point out a much greater number consisting of species improperly united. One very remarkable case of this kind is the genus

Galea,

to which, as I intend to enter fully into the history and affinities of its species, I shall confine myself.

This genus was established by Linneus in the sixth edition of his Genera Plantarum, where the natural character is given: but the following essential character, which is still retained, appears for the first time in the twelfth edition of Systema Naturae, in the third section of Polygamia aequalis: "Receptacidum paleaceum, Pappus pilosus, Calyx imbricatus." The species originally referred to Calea, in the second edition of Species Plantarum, are C.jamaicensis, oppositifolia, and Amellus, described from specimens in Browne's Jamaica Herbarium, which he had received a few years before, and incorporated with his own.

These three plants Linneus had originally referred to Santolina*, for which it seems to me rather less difficult to account than for his afterwards uniting them together to form his genus Calea; two of them, according to his descriptions†, though in reality one only, being without pappus, and in other respects corresponding with the generic character of Santolina; and the third, which

In Amoenit. Acad. vol. v. p. 404. † Loc. cit.

Yet, in opposition to this view, I have in a single instance found one of the divisions of the urceolus in Pæonia Moutan changed into an anthera; and the divisions of the apparently analogous organ in Aquilegia, which in their usual state resemble barren filaments, have sometimes been observed with perfect antheræ^[5].

↑ Of 1813 and 1814.
↑ Tabulæ affinitatum regni vegetabilis.
↑ In Botanisches Handbuch.
↑ To the arguments I have adduced (in my Remarks on the Botany of New Holland) in support of this opinion, I am now enabled to add the more direct proof derived from certain species of Euphorbia itself, in which the female flower is furnished with a manifest calyx. I have formerly observed, that in a few cases the footstalk of the ovarium is dilated and obscurely lobed at top: but in the species now referred to it terminates in three distinct and equal lobes of considerable length, and which being regularly opposite to the cells of the capsule may be compared to the three outer foliola of the perianthium of Phyllanthus, between which and the cells of the capsule the same relation exists. This calyx is most remarkable in an undescribed species of Euphorbia from the coast of Patagonia, in the Herbarium of Sir Joseph Banks; but it is observable, though less distinct, in E. punicea and several other species.
↑ Schkuhr Handbuch, tab. 146.

[1] Of 1813 and 1814.

[2] Tabulæ affinitatum regni vegetabilis.

[3] In Botanisches Handbuch.

[4] To the arguments I have adduced (in my Remarks on the Botany of New Holland) in support of this opinion, I am now enabled to add the more direct proof derived from certain species of Euphorbia itself, in which the female flower is furnished with a manifest calyx. I have formerly observed, that in a few cases the footstalk of the ovarium is dilated and obscurely lobed at top: but in the species now referred to it terminates in three distinct and equal lobes of considerable length, and which being regularly opposite to the cells of the capsule may be compared to the three outer foliola of the perianthium of Phyllanthus, between which and the cells of the capsule the same relation exists. This calyx is most remarkable in an undescribed species of Euphorbia from the coast of Patagonia, in the Herbarium of Sir Joseph Banks; but it is observable, though less distinct, in E. punicea and several other species.

[5] Schkuhr Handbuch, tab. 146.

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Transactions of the Linnean Society of London/Volume 12/Some Observations on the natural Family of Plants called Compositæ

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