FLORAL ANATOMY OF SOME COYPOSIT&. 517

On the Floral Anatomy of some Composits. By JAMES SXALL, M.Sc.(Lond.), Lecturer in Botany, burham University. (Communicated by Prof. M. C. POTTER, M.A.,Sc.D., F.L.S.)

(1 Text-figures.)

[Read 30th November, 1916.1

THERE have been numerous observations on the venation of ilic corolla in the Cornposits (2, 4, &c.) ; the vascular supply of the ovule ( G , 8, 14, 18, 19) and the style (6) has also been the subject of enquiries, and there are also records of the structure of the pericarp in many species (3, 6, '7, 9); but, except in the Cichoriere (15, 16, 17), no complete study of the vascular system of the flower appears to have been made. The observations of Trdcul confirm the striking uniformity of the vascular supply of the corolla in the CichorieE, which seems obvious from the external examination of tlie venation of a large number of species and genera belonging to this group. The present investigation deals with the floral anatomy of three typical forms of florets-tubular, ligulate, and bilabiate or pseudo-ligulate. As it has been suggested that the Cichories were derived fioiii the Seneciones (10,12), it was thought that the examination of the linear ray florets in Tus- siiago Parfara might show an intermediate stage between the two group9.

The anterior lip of the labiate or ray floret in the Compositz is freqaently four-lobed, especially where the corolla is broad, as in some species of Creman- thodium (6'. rhodoceplialum, Diels, C. Decaisnei, C. B. Clarke, C. renijorme, Benth., C. Tliomsoni, C. B. Clarke). The vascular supply is modified accordingly. The corolla may be broad and still only three-lobed, as in Layia elqans, Torr. & Gray, or i t may be three-lobed with a vascular sllpply for four lobes, or the lobes may be fused so that the number varies from one to three, while the number of conducting strands remains the same. When the anterior lip is broad the condiicting strands tend to increase in number, the simplest modification being the development of three auxiliary strands in the position of the midribs of the three petals. Branching of the strands may take place to a varying degree, and usually occurs in the ahove- mentioned species of Cremanthodium and in inany Senecio species, as well as in iiiany other cases where the number of main strands remains three or four or by fusion becomes less thiln three. The number of strands in S. Doronicum, Linn., varies from four to eight, and in S. eubeus, Boiss. & Heldr., may be as many as eleven, but it may be larger in other species (e. g., Heliunthus SPP.).

The vascular system of the ovule has been the subject of many obser- vations and some controversy, but it does not seem to have any bearing on the problems of phylogeny. The occurrence of anomalous biovulate and

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518 MR. JAMES SMALL ON THE

bilocular ovaries in the typical genus of the order (13) is much more illuminating. The vascular supply of the corolla, on the other hand, seeins to fnrnish a means of distinguishing between the bilabiate and the ligulate types of corolla in certain cases where the distinction is not obvious. Tiissilago is one of these. The my florets are very numerous and form several rows, enclosing a relatively small number of male disc florets. Without a detailed examination of the conducting tissue i t seemed possible that this was a truly ligulate corolla with the five teeth a t the tip completely fused or aborted.

Senecio vulgaris may be talcen as a species with a typical tubular floret, and a brief description of the conducting tissue of these florets will furnish a basis for comparisons. A model of the vascular system was constructed, of which fig. 1 is a sketch; the conducting strands of the stamens are indicated by thin lines, and those of the ovule and style by dotted lines. I n fig. 1 the lines by the side indicate the position of the sections with the corresponding numbers in fig. 2 , and the position of the axis is indicated by an arrow. The diagrams in fig. 2 are so orientated that the posterior part of the flower is a t the left, and ihe shaded regions in diagrams 5, 6, and 15 indicate the position of the nectary. The conducting tissue is coinposed of a few vessels and numerous elorigated cells with more or less lignified walls.

A single strand from the receptacle enters the flower and spreads a t the base of the ovary, giving what may be called the lower distributive centTe (fig. ’2, diag. 1). E’rom this more or less disc-shaped inass ten bundles are given off to supply the wall of the ovary (fig. 2, diag. 2) and R single bundle to supply the ovule. Towards the top the ten bundles fuse in pairs (fig. 2, ding. 3), and a Iittde higher up there is a series of anastomoses constituting an y v p e r distributive centre (fig. 2, diag. 4). Prom this centre are giren off five bundles, which alternate with the fused petals (fig. 2, diag. 5 ) , and a short distance above the zone of anastomoses divide Lingen- tially to supply the stamens and corolla (fig. 2, diag. 6). The stamina1 bundles remain near the corolla bundles within the tissue of the corolla-tube until the filaments are differentiated (fig. 2, diag. 7), and they end in the connectives (fig. 2, diag. 8). The two bundles of the style are given off from the upper distributive centre (fig. 2, diag. l i), and the anastomosiog of the five niain bundles in this region is probably required on account of the want of symmetry, five strands dividing to give the two stjlar and five corolla strands. Tr6cul (15) finds that in the Cichories the stylar bundles are usually inserted upon the lateral bundles of the ovary, but he remarks on tile \fariation shown and does not seem to have observed the upper and lower distributive centres.

The lower distributive centre can be compared to the region of fusion in Pamassin, and the “ raison d’ktre ’’ of the complications of the upper distributive centre is evidently somewhat similar to that suggested by

FLORAL AKATOMY OF SOME COMPOSITZ. 319

Arbttr (1) for the fusion in that genus. In Tussilugo E’arfbm, where there is more symmetry, the upper distributive centre is much less complicated.

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FIQ. l.-Vseculer sptem of tubular floret of Senccio zrtlyaiia.

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FIG. 2.-Semi-diagrammatic sections of the florets of Senecio zxdywia (disgs. 1-EC), Tararacurn o$icinale (diags. 9-11), Calendula o@inaZis (diags. 12-16).

520 MR. JAMES SMALL ON THE

AS both Brown (2) and Don (4) remark on the facility with which the embryo can be extracted from the ovary adherent to the two strands which supply the style and which, according to these authors, continue without a break down the wall of tho ovary, all the material was examined specially for such bundles. The stylar canal is lined with elongated cells and these become lignified and persist on the lat,eral sides of the mature ovary as conducting strands (fig. 2, diags. 2-3), but seem to act only secondarily as conducting tissue. Brown (2) gives the orientation of the stylar bundles correctly as antero-posterior and describes the ovarial strands as lateral. The lateral position of these strands, which are not a part of the true vascular system, is due to the developing embryo bursting the stylar canal on the anterior and posterior sides. The five corolla bundles divide a t the base of the corolla lobes, and the halves unite to form five arches of con- ducting tissue along the margins of the lobes.

I n TaraxacunL oficinale, an example of the ligrilate type, the coiirse of events is very similar. The primary strand from the receptacle divides only into .five * strands and the ovular supply (fig. 2, diag. 9). I n this case the cells lining the stylar canal do not become lignified, and there is no trace of the bundles referred to by Brown and Don. There are again the upper and lower distributive centres, and a short distance from the former the posterior slrand divides into three (fig. 2, diag. 10). The inner strand supplies the posterior stamen and the other two supply the margins of the ligulate corolla (fig. 2, diag. 11). According to Tr6cul (15) the point of fusion of these two marginal bundles varies from the upper distributive centre to some distance above the top of the ovary.

I n the ray or bilabiate florets of Culedula oficinulis the single primary strand divides soon after or even before it leaves the receptacle, giving two large bundles and the ovular supply (fig. 2, diag. 12). Fusions begin towards the top of the ovary (fig. 2, diag. 13). The upper distributive centre shows new features (fig. 2, diag. 14) obviously dependent upon the absence of a posterior bundle, and from this centre arise the two stylar bundles, the two main corolla bundles, and two subsidiary corolla bundles (fig. 2, diags. 15 & 16). The cells lining the stylar canal become lignified and peraist as in Senecio vulgaris (fig. 2, diags. 12 & 13). The stamens are absent, and there is no trace of the bundles which presumably supplied them in the hermaphrodite condition of the floret. It is uncertain to what extent the vascular system of the bilabiate floret in Culeadula ofidnulis is typical of ray florets in general.

The disc florets of C. o$cinaZis are very similar to those of Senecio vulgaris, escept that only five bundles and the ovarial supply originate from the lower distributive centre instead of ten as in the latter species.

* Tr6cul (16) gives usually four, rnrely five, 'bundles.

FLORAL ANATOMY OF SOME COBIP08ITE. 521

Considering now the anatomy of the bilabiate florets in Il‘ussilago Parjara, we find the same priniary bundle as in Senecio w1,yaris and l’araxacuni oficitiale (fig. 4, diag. 1) and the same lower distributive centre (fig. 4, diag. 2). The bundle at this stage in 7‘. Parfara is more clearly defined than in the other cases, being a well-marked disc from the interior of which arise five strands, four to supply the periphery of the ovary and the fifth to supply the ovule (fig. 4, diags. 3 & 4). The anterior bundle is usually larger than the others, even at this stage. There is some variation in the number of the peripheral bundles, five occurring frequently and the number may increase to six, seven, or eight. All these fuse at the upper distributive centre, and above that point four is the constant number. The upper distributive centre is clearer and shows more symmetry than in the other species examined. There are two well-defined arcs with the lateral bundles in the centres of the arcs ; these two arcs are joined at their anterior and posterior ends by two shorter arcs with arms forming sectors (fig. 4, diag. 5) . Froin the points of the sectors arise the two stylar bundles (fig. 4, diag. 6 ) . At this stage the somewhat rudimentary pappus shows many interesting stages in the “ splitting ” of this solid ring of tissue into the numerous hairs of the mature pappus, which are multicellular a t their bases, but split higher up into hairs which are unicellular in cross-section. The pappus has no vascular supply.

The posterior bundle soon coines to an end, and the corolla remains a tube with three conducting strands (fig. 4, diag. 7). The lateral strands continue in a very attenuated form, supplying the margins of the corolla after the tube splits to give a distinct lip (fig. 4, diag. 8) *. The style remains unbranched up to this point, but higher up it branches and the Conducting strands become merged in the elongated cells of the layer below the stigmatic papillae (fig. 4, diag. 9). Beyond the style the lip becomes flattened (fig. 4, diag. lo), and the :interior bundle extends almost to the tip of the corolla. The cells lining the stylar canal become lignified ; the stylar canal is burst on the anterior and posterior sides by the developing embryo and the lignified cells persist after the degeneration of the surrounding parenchyma, forriling two secondary conducting strands one on each side of the embryo (fig. 4, diag. 3). These strands are more conspicuous in this species than in most, and Brown (2, p. 89) mentions Tussilago odorata t as another species in which these “ cords” are easily separable from the “ ovarium.”

Fig. 3 shows the complete vascular system, and this figure and the diagrams of fig. 4 are arranged so that the posterior side is at the left as in figs. 1 & 2.

* I u the few case8 where there are two main bundles in the anterior lip, one of these is shown by the examination of serial sections to he an nbnormally well-developed lateral bundle and the symmetry in the corolla-tube is of the usual form.

t PI obably P e t n a i h fmgrana, Presl.

522 MR. JAJIES 6MALL ON THE

The male disc florets of Tussiluyyo E’urfaru are tiibular ; the style persists as a pollen presenter, and it is intoresting to note in connection with the explanation given by Arber (I) of the vestigial bundles in Pamzassia that there are f o w vascular bundles in the styles of these florets where the

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FIQ. 3.-Vsscular system of ray floret of Trcasilago Farfnra.

FIQ. 4.-Semi-diagrnmmatic Bectione of the ray florets of T. Fmfara (diaps. 1-10) and of the diec florets (dings. 11-20).

FLORAL ANATOMT OF SOME COMPOSITX. 523

original function of the style has been lost and a secondary function acquired, which requires, if anything, more rigidity in the style than does the original function *. A similar case is that of Arctotis aspera, previously reported on (11) in connection with an irritable pollen-presentation mechanism. Here the comparatively thick style remains upright and undivided during the male stage, and an examination of hand-sections shows the presence of four vascular bundles in the lower half of the thick part of the style. The two lateral bundles end near the separation of tho style branches.

The lower distributive centre in these male florets of T. Farfara (fig. 4, diag. 12j is similar to that in the ray florets, but the ring is not so well marked and only an abbreviated vestige of the ovule remains (fig. 4, diag. 13). I n the upper distributive centre (fig. 4, diag. 15), which is also similar, the two lateral bundles supply the two lateral stylar bundles ; the two anterior bundles supply the anterior stylar bundle ; and the posterior biindle supplies the posterior stylar bundle. The cavity of the ovary persists, as do the strands of the stylar canal (fig. 4, diags. 13 & 14). The short pappus is a single row of laciniae, nol a double row as in the ray florets (fig. 4, diags. 6 8: 16). The five lobes of the corolla are longer than in SmPcio vulgaris (fig. 2, diag. 8 & fig. 4, diag. 19), and the tips of the lobes show the s:ime fusion of the divided strands (fig. 1 & fig. 4, diag. 20) as in the latter species. The four stylar bundles end near the base of the aborted stigmatic region.

It will be seen from the foregoing acconiit that, while the anatomy of the ray florets in Tussilago Fwfara differs considerably from that of the ray florets of Calendula oficinalis, it shows no similarity to that of the ligulate type which is so constant a feature of the Cichorieac. The constancy of the one particular type of floral anatomy in the Cichorieae thus enables 11s to eliminate definitely Tussilago Farfara as an intermediate type. The vascular supply of the bilabiate corolla seems to vary with the width of the nnterior lip, and the single main strand of the very narrow lip in 'Licssilap Farfirm is to be considered with the other variations mentioned, such as the increase in number of the bundles when the anterior lip is wide, :IS developed in response to the needs of the corolla.

Acknowledgments are due to Professor M. C. Potter for access to books and periodicals.

A curious difference between these male florets nnd the female rnp florets is the very complete protective modification of the free msrgincc of the petah. In the male florete tho marginal epidermal cells are elongded to form tooth-like protuberances which in the bud fit exnctly into those of the sdjacent margins even up to the extreme tips of the five loben, while no such protective device is preseiit in the ray florets, where from a very elrrly stage the style is free and unprotected by the corolla. This may be due to the amheaponurn being the region which requires protection.

524 MR. JAXES SMALL ON THE

SUnf\f.4RY.

1. The vascular anatomy of the tubular florets of Senecio vulyaris, the ligulate ff orets of 7’ara.raczim @ciaale, and the tubular and bilabiate florets of Calendula oJicinalir, and Tussilago Farfara are described in detail.

2. The vascular supply of the ray florets of the last species is discussed, and any suggestion of T. Pmfara being a type intermediate between the Seneciones and Cichories is uegatived.

3. The conclusion is reached that the ligulate florets of the Cichoriea have a comparatively constant type of vascular anatomy ; that the tubular disc- floret3 show a slightly greater variability, while the rariation in the vascular anatomy of the bi1at)iat.e ray florets is so great that they can be distinguished froin the first two classes by the floral anatomy alone.

BIBLIOQRAPEY. (1) ARBER, A.-On the Structure of the Andrmium in Pnmassia. Annals

(2) BROWK, R.-Some Observations on the Natural Family called Trans. Linn. SOC. vol. xii., 1818.

(3) CAPUS, G.-Anatomie du tissu conducteur. Ann. Sci. Nat., Bot.

(4) DON, D.-(a) On the Origin and Nature of the Ligulate Rays in

( I ) ) An Attempt a t a New Classification of the Cichories.

(5) GUEGliKE;, M.-Analomie coinpartb du tisw conducteur du style et du

(6) GUIQXARD, L.-Recherclios sur le tl6veloppeiiient de la grnine et en Journ . de Botanique, t. vii.,

(7) L ~ V I A L L E , P.-Rechcrches sur le ddveloppement de l’ovaire en fruit

(8) 1,e MONNIER, G.-Recherches SUP la nervation de la graine. Ann.

(9) I,OOSE, R.-Die Bedeutung der Frucfit und Samenschale der Com-

(10) SMALL, J.T-TIie Pollen-Presentation Mechanism in the Compositp.

(11) - Preliminary Observations on the Pollination Mechanism of

(12) - New Phytologist,

of Botany, vol. xxvii., 1913.

Compo&e.

60 sCr. t. vii., 1878.

Zin~2ia.

Edin. New Phil. Journ. 1 7 0 1 . vi., 1828.

Trans. Linn. Soc. vol. xvi., 1829.

stiginate tles Phanbrogams. Paris, 1901.

particulier clu t6gument seinind. 1893.

chez les ComposBes.

Sci. Nat., Bot. 5‘ sir. t. xvi., 1872.

p s i ten. Inaugurnl-Dissertation, Berlin, 1891.

Annals of Botany, vol. xxix., 1915.

d r c t o t i s aspera, L.

vol. xv., 1916.

Ann. Sci. Nat., Hot. 9 sdr. t. xv., 1912.

New Phytologist, vol. siv., 1915. Notes on the Corolla in the Composik.

FLORAL ANATOMY OF SOME COMPOBITE. 535

(13) SMALL, J.-Anom:ilies in the Ovary of Senecio vulgaris, L. . Annals of

(14) STRASBURQER, E.-Angiosperinen uiid Gymnosperinen. (15) T R ~ C U L , A.-Ordre d’apparition des vaisseaux dans les fleurs tie quelques

(10) - De I’ordre d’apparition des vaisseaux dans les fleurs d u Taraxa-

(17) -- De l’ordre d’apparition des vaisseaux dnns les fleurs de quelques

(18) VAN TIEQHEM, F.-Note siir les divers modes de nervation de l’ovule et

(19) WARYINQ, J. E. B.-De I’ovule. Ann. Sci. Nat., Bot. 6“ s6r. t. v.,

Botany, vol. xxx., 1916. 1879.

Tragopogon et Scoreonera.

cum Dens-leonis.

Lactuca.

de la graioe.

1878.

Coiiiptes Rendus, t. cxi. p. 327, 1890.

Coinptes Rendus, t. cxiv. p. 446, 1892.

Comptes Rendus, t. cxv. p. 86, 1892.

Ann.-Sci. Nat., Bot. 5“ skr. t. xvi., 1872.

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