THE peculiarities in ovule production described in the following

Transcription

1 [42] ABNORMALITIES IN THE OVARIES OF HELIANTHUS DECAPETALUS LINN. VAR. MULTIELORUS BAILEY BY COMYNS J. A. BERKELEY, B.Sc. Day College of Science, Chelsea Polytechnic (With 38 figures in the text) THE peculiarities in ovule production described in the following account were originally fijund in specimens of Helianthus decapetalus Linn. var. multiflorus Bailey received for class work at the Chelsea College of Science, from the L.C.C. Botany Scheme Offices, Avery Hill, Eltham, S.E. The plants were grown in the Avery Hill Nursery. The specific and varietal names were confirmed by Dr W. B. Turrill, to whom thanks are due also for criticism and suggestion during the research. NORMAL CONDITION OF THE OVARY IN THE COMPOSITAE The ovary in the Compositae is formed of two median anteriorposterior carpels which unite at the edges; the single ovule springs from the floor of the chamber, slightly below the centre, in front of the middle line of the anterior carpel (8). The o\aile is erect and anatropous ((13) and (7), p. 379, Eig. 310) and its raphe is apparently normally anterior (in, 14). Before fertilisation the single integument forms the mass of the ovule; it is thick and solid and overtops the small nucellus ((7), p. 382). Brown (2) says that in the greater part of the Compositae he examined, two filiform cords ("cordulae") \yere observed originating at opposite points on the base of the ovule or its stalk and running up the sides of the ovary to unite under the style. In Liastris spicata and Tussilago odorata they were easily separable from the ovary wall. In species where they were not obvious he assumed them to be intimately connected with the wall. He regarded the cordulae as occupying the positions of parietal placentae, and supposed each to be formed by the confluence of two cordulae, one from each carpel. Don (5) found in Zinnia sp. that the cords could be readily seen, traced up to the stigmas, and removed from the ovary with the ovule still attached between them.

2 Abnormalities in Ovaries 43 PREVIOUS OBSERVATIONS OF ABNORMALITIES Goebel ((7), p. 378) mentions a small prominence visible beside the funicle of the ovule, which in abnormal instances may grow into a leafy shoot. Both he and Coulter and Chamberlain (3) regard the ovules as lateral shoots of the floral axis. Schwere(9) reported a specimen of Taraxacum offieinale having two ovules in the ovary. The ovules were apparently basal. Don(5) describes in a number of species of Zinnia two to five "embryos" clustered in the ovaries of flowers having otherwise increased numbers of parts. He also found that it was not unusual for florets, normal except for an increased number of stigmas, to show monstrous "embryos" with several dolabriform "cotyledons" and a long filiform "radicle." Small (10) figures sections of three abnormal ovaries of Senecio vulgaris. In all of them ovules arose from the side of the ovary. In one the ovary was unilocular and bore a single lateral ovule; in another the ovary was unilocular and one ovule arose from each side of it; in the third the ovary was bilocular and showed two ovules arising from the same side of the ovary but in different loculi. ABNORMALITIES IN HEUANTHUS DECAPETALUS var. MULTIFLORUS Preliminary examination and working methods During class work it was found that certain inflorescences contained ovaries with more than one ovule in them, and that these abnormal ovaries were often located in the centre of the inflorescence. Later all inflorescences available were searched for florets having otherwise increased numbers of parts. None were found. The inflorescences available were spht in halves, a few ovaries removed from each and their contents examined. Those inflorescences found to contain abnormal ovaries were set aside for detailed examination. Corollas, etc., were removed and diagrams constructed to show the arrangement of the florets in the capitula. Each floret was located by two numbers, one (Roman figure) indicating an arc of florets and the other (Arabic flgure) the sequence of the floret in the arc. The ovaries were then removed from the inflorescences, commencing at the centre and working to the right round the arcs. As each ovary was removed it was split in an anterior-posterior plane, examined under a dissecting microscope and, if showing abnormality, drawn. The drawings of abnormal ovaries were numbered to correspond with the ovary distribution diagrams and the latter

3 44 CoMYNs J. A. BERKELEY built up as the ovaries were removed to show distribution of abnormalities. Ovaries were selected for microtoming as follows. All ovaries wciv removed from capitula known to contain abnormal ones, and after being fi.xed and washed were cleared in xylol. Each was then placed ovc r a suitably shaped aperture in a black card and e.xamined by transmitted light. By this method it was possible to separate, without dissection, ox-aries containing more than one ovule from the others. Selected ovaries were embedded in paraffin wax and microtome sections o-o2 mm. thick were cut. These were drawn with the aid of a camera lucida. Variations in the contents of the ovaries Many of the ovaries examined were normal, containing ovules apparently arising in the orthodox position from the bottom of the ovary cavity. In some, however, although the raphe was anterior the micropyle was not strictl}' posterior; it could be seen under the dissecting microscope much more distinctly when the ovule was viewed from one side than when \'iewed from the other. Thus the line joining the middle of the raphe with the micropyle runs obliquely across the ovary. In some ovaries there arose from the side of the normal ovule near its point of attachment a thin filament that grew in contact with the ovary wall up its mid-lateral line; in others two such filaments were seen. These correspond to the cordulae of Brown (2). Certain ovaries showed the filament to be refiexed at some point in its course as a strand freely pendent in the ovary cavity (Figs, i and 2). In a few this freely pendent strand bore at its apex a simple distension (Fig. 3), while in others the swelling took the form of a bilaterally symmetrical structure tipped with yellow hairs (Figs. 4-8). In another series an additional o\aile pendent from the side of the loculus near the top, and often resembling in outward form the normal basal one, took the place of the apical swelling (Figs. 9, 10). In one ovary the additional pendent oviile had two lobes (Fig. 11) and in a few two ovules arose from the upper part of the loculus. One ovary contained two basal ovules and one pendent one (Fig. 12). There was no uniformity as to the side of the ovary from which the additional ovules arose. Capitulum i (Fig. 13) bears sixteen on the left, two in the centre and seven on the right of its ovaries.

4 Abnormalities in Ovaries 45 Distribution of abnormal ovaries in capititla The abnormal ovaries invariably had a tendency to be massed in the centre of the inflorescences and, as a rule, there was a rough gradation from greatest to least degree of abnormality ranging from the centre of the capitulum outwards (Fig. 13, ovaries ii, i; iv, i; vi, i; and Fig. 14, ovaries i, i; ii, 3; ii, 4). Origin of the vascular bundles of the cordnlae Abnormal ovary i (Figs ) was sectioned from the base upwards and as a consequence its parts are correctly orientated. The lowest sections obtained show a V-shaped group of vascular bundles in the anterior half of the ovary and one bundle already preparing to divide in the posterior edge (Figs. 15, 16). The anterior group soon comes to contain three bundles larger than the rest (Fig. 17). One of these runs up the anterior edge of the ovary, and the other two, at first on the extremities of the arms of the V, gradually work themselves into the space between the arms. As they do so they give off a number of smaller bundles that increase the length of the arms (Figs. 17, 18, 19). The single posterior bundle divides and a large strand of vascular elements separating from it wanders to the centre of the ovary (Figs. 16, 17). Two other vascular strands are subsequently given off from the main posterior bundle (Fig. i8) and these also make their way to the centre, branching as they do so, to establish a posterior V of similar construction to the anterior one (Figs. 18, 19). They then come to lie in an arc of bundles on the posterior side of the main central one, the arc having been formed by the splitting of bundles of the posterior V (Figs. 19, 20). The large bundles that have passed to the centre from the margins of the anterior V unite with the main central bundle, and are followed by the posterior arc to form a ring of vascular tissue in the centre of the ovary (Figs. 20, 21). This ring of vascular tissue subsequently divides into three (Fig. 22). The middle bundle of the three becomes the bundle supplying the normal ovule, while the two lateral ones pass up the midlateral lines of the loculus as bundles of the cordulae (Figs ). It is believed from the way in which union and subsequent separation of the vascular tissue occur that the bundles of the cordulae may be considered as formed each by the confluence of the two extreme bundles of the V's on the same side of the ovary. This is in agreement with Brown's conceptions of the cordulae (2).

5 CoMYNS J. A. BERKELEY Figs

6 Abnormalities in Ovaries 47 The figures are arranged in the sequence in which they are first mentioned in the text. Figs. I to 12 illustrate types of abnormality found in ovaries. All except Fig. 3 were drawn from material from capitulum depicted diagrammatically in Fig. 13, and except where otherwise stated are x 2-5 approx. Figure numbers and ovary numbers in relation to Fig. 13 are as follows, respectively: I =v, 7; 2 =vi, 2; 4 =iii, 6; 5 =tip of pendent filament in iii, 6 ( X 20 approx.); 6 and 7 =right and left sides of vi, i; 8 =tip of pendent filament in vi, i ( x 40); 9 and 10 =left and right sides of iii, 5; 11 =iii, 2; 12 =i, 2. Fig. 3 =v, 5 of another capitulum which is not shown diagrammatjcally. Figs. 13 and 14 are diagrammatic representations of half capitula numbers i and 2 to show distribution of abnormal ovaries. Fig. 13 was constructed from material collected in 1928, Fig. 14 from material collected in Triangles represent ray florets and rhombs disc florets. A line running into the rhomb and bisecting one of its obtuse angles indicates a simple pendent filament on the corresponding side of the ovary. A similar line tipped with a spot indicates in the same way a filament expanded at its apex. A black triangle in the obtuse angle of the rhomb similarly represents an additional ovule attached to the side of the ovary shown. A spot in the centre indicates an additional basal ovule. Roman figures are placed opposite the first ovules of the arcs referred to in the text. Arabic fignres numbering the florets in the arcs are omitted for the sake of clearness. The arcs may be traced readily by commencing at arc i and striking out the two ovules it contains in each capitulum; then passing to arc ii and striking out the five florets next outside those in arc i, and so on. Figs. 15 to 37 are copies of camera lucida drawings of selected transverse sections of abnormal ovaries, all x 13 approx. In every case the anterior part of the ovary is nearest the bottom of the sheet. Figs. 15 to 25 are from sections of abnormal ovary 1 and illustrate the origin and course of the vascular bundles of the cordulae at the lower end of the fruit. Figure numbers and section numbers correspond as follows, respectively: 15=1; 16=2; 17=4: 18=8; 19=15; 20=17; 21=29; 22=34; 23=50; 24=53; 25=141. Fig. 24 also shows the "lateral" attachment of the normal ovule and its laterally directed niicropyle. Fig. 25 also shows the normal and additional ovules, the latter, though sectioned below its point of attachment, indicating by its orientation attachment to the right-hand cordula by means of an anterior funicle. Figs. 26 to 34 are from sections of abnormal ovary 2 and illustrate the termination of the vascular bundles of the cordulae in the upper end of the fruit and the disappearance of one soon after it enters the loculus. The loculus and its contents only are shown in Figs. 31 to 34 (ovary was sectioned from top to bottom, hence parts are laterally transposed). Figure numbers and section numbers correspond as follows, respectively: 26=14; 27=19; 28=26; 29=46; 30=52; 31=84; 32=212; 33=314; 3.4=322. Fig. 31 also shows the lateral attachment and laterally directed micropyle of the additional ovule. The main mass of the ovule is here posterior to the funicle. Fig. 32 also shows the lower part of the ovule with its main mass anterior to the side of funicle attachment. Fig. 33 also shows the "lateral" attachment of the normal ovule and its laterally directed micropyle. Fig. 34 shows the reappearance of the left-hand cordula. Figs. 35 to 37 are from sections of abnormal ovary 3. Ovary was sectioned from bottom to top and hence parts are correctly orientated. Figure numbers

7 48 CoMYNS J. A. BERKELEY In all material examined, both of abnormal and of normal ovaries, the above holds true up to the point of union of vascular tissue in the centre. Abo\'e this, one or both cordula bundles may be so small as to be almost inappreciable. Where one large bundle and one small one are found an additional ovule usually arises from the larger. Two very small cordulae were found only in normal ovaries. Termination of the bundles of the cordulae in the upper end of the fruit There are five bundles in the lower part of the style. About its point of attachment to the ovary the central bundle of the five divides into two smaller ones placed right and left. Six bundles pass into the top of the ovary and the four outer ones run obliquely outwards to merge with the general ring of bundles in the ovary wall (Figs. 26, 27, 28). The two smaller central bundles may usually be traced through the top of the fruit into the loculus where they become the bundles of the cordulae. In some ovaries both the bundles are obvious throughout the whole length of the ovary; in others, one or both bundles may become so small as to be inappreciable. Thus in abnormal ovarj' 2 (Figs ) the right-hand bundle remains large and gives rise to the vascular tissue that supplies an additional ovule, but the left-hand one is inappreciable at the level of section 52 (Fig. 30). It is obvious again, however, at the level of section 322 (Fig. 34) where the normal ovule is attached. Attachment of additional ovules and direction of their micropyles Sections of all the abnormal ovaries cut showed the additional ovules to be attached to the side of the loculus and to have vascular tissue arising from that of the cordula. Moreover, though the main mass of the ovule was placed longitudinally in the loculus, the micropyle was always directed to the side of attachment (Figs. 31, 37). No truly pendent ovules were obtained in sections. Position of funicles of additional ovules In most sections examined the funicles of the additional ovules occupied an anterior position (Figs. 25, 36, 37). A few ovaries conand section numbers correspond as follows, respectively: 35 =46; 36 =180; 37=245- Fig. 35 shows the "lateral" attachment of the normal ovule and its laterally directed micropyle. Fig. 36 shows the additional ovule orientated in such a way that its funicle is obviously attached to the left-hand cordula and is anterior. Fig. 37 shows the actual attachment of the additional ovule to the left-hand cordula and its lateral micropyle.

8 Abnormalities in Ovaries 49 tained additional ovules whose main mass was direeted away from the point of attachment towards the anterior side of the cavity (Fig. 32). When, however, higher sections of the same ovaries are examined it is found that attachment of these additional ovules is similar to that of additional ovules with anterior funicles (cf. Figs. 31, 37), and the impression is gained that the orientation of the former has been reversed during growth. This reversal is believed to be due to mutual pressure between ovaries during development; the ovary figured in Figs bears obvious signs of distortion in a clockwise direction when viewed from the top, and such distortion would tend to rotate the ovule in the direction required to bring about the suggested reversal of orientation. Attachment of normal ovules and direction of their micropyles The normal ovules in abnormal ovaries were constantly found to be attached for a greater distance up one side of the loculus than the other (Figs. 24, 33 and 35). This could not have been due to the angle at which the sections were cut; thirty-three sections each 0-02 mm. thick intervened between section 53 (Fig. 24) and the final separation of the ovule from the left-hand wall (ovary sectioned bottom to top, hence parts laterally transposed). The loculus is 0-9 mm. across, and hence an error of about 40 degrees would be necessary to produce the difference in height of the two sides. This angle would have been obvious both in the block on the microtome and in the sections. Correlated with this "lateral" attachment was the fact that the micropyles of normal ovules in abnormal ovaries were always directed to the side of highest attachment. In normal ovaries with small cordulae the micropyle of the ovule was constantly found to be central and the attachment truly basal. DISCUSSION Nature of the cordulae Since the additional ovules are attached to the cordulae these must be regarded as placentae, a view that agrees with one of Brown's conceptions (2) as to their nature. Moreover, each seems to be formed by the confluence of two strands of tissue, one from the anterior and one from the posterior V of vascular tissue in the base of the ovary, and if this be accepted then there can be no doubt that tlie PHYT. XXX. I 4

9 50 CoMYNS J. A. BERKELEY four bundles which unite in pairs to form the cordulae are the marginal bundles of the two carpels. Bearing on the relationships of the Compositae It is generally accepted that the multiovulate condition is primitive. This condition calls for large placentae and a corresponding amount of vascular tissue and it would appear that since, in the material described, placental tissues are present in increasing quantities as the ovarv' becomes more abnormal, the ancestral condition is being approached by reversion. If this be admitted then attachment of the ovules to the walls of the loculus is an ancestral character. Not only were all additional ovules found to show this attachment, but the direction of the micropyles also indicated outgrowth from the side wall. These facts fit in with Small's descriptions of anomalies in the ovaries of Senecio vulgaris{\n) where he mentions many instances of ovules arising from the side of the ovary cavity, and the whole of this research would seem to uphold his views as to the relationships of the Compositae. As regards the Calyceraceae he disagrees with Warming who says that they should be removed from the neighbourhood of the Compositae and placed near the Dipsacaceae. Warming holds that the displacement of the ovule of the Compositae, so that it became pendent, would give it a position very different from that of the Calj'ceraceae and the Dipsacaceae (14). Small points out that if such displacement took place in a lateral plane, as he would expect in an ovary derived from two anterior-posterior carpels, then the Compositae would agree with the Calyceraceae in having pendent ovules with anterior funicles. In the material here described, though no ovules actually pendent from the top of the loculus were sectioned, many were attached near enough to the top to show that displacement does take place laterally and that, having reached the pendent position, the ovules have anterior funicles. In another paper (11) Small deals with the possible origin of the Compositae from the Lobelioideae. The ovary in the latter family is typically bilocular with axile placentation, but Rhizoeephalum and Apetahia have their numerous ovules attached to the side walls and Lysipoma has a few basal ovules. These three genera Small uses as links connecting the Lobelioideae to the Compositae. In his paper on Senecio(V)) he points out the similarity between the abnormalities he describes there and the normal condition in Rhizoeephalum and Apetahia. The present research undoubtedly proves in Helianthus not

10 Abnormalities in Ovaries 51 only that ovules may arise laterally, as in these two genera, but also that more than one may be found attached to the base of the loculus as in Lysipoma. Moreover, if the interpretation here suggested for the origin of the bundles of the cordulae be accepted, then there is in the base of the ovary, where the four marginal bundles of the Vs unite, a condition comparable witb what one would expect in a bilocular ovary with axile placentation. Erect condition of the ovule in the Compositae It has been pointed out that, in abnormal ovaries, though the main mass of each ovule is placed longitudinally in the cavity, the micropyles are directed towards the side of attachment. Now if we deduce from this that the ovules arose laterally as did those in Senecio (10), then it would be logical to assume tbat the relatively small loculus compared with the size of the ovules led to the ovules being forced to take up a longitudinal position. Naturally, if they were attached near the top of the cavity, they became pendent and vice versa. It is suggested that this may have been a factor in the origin of the erect ovule in the Compositae. If one imagines the ancestral stock as having many small ovules and, at some time in evolution, large ones arose, then mutual pressure of the ovaries together with limitations in food supply set by tbe vascular tissue of the axis would prevent enlargement of the ovaries and at the same time limit the number of ovules tbat could mature. Those nearest the source of food, i.e. the base of the ovary, would tend to succeed at the expense of the others and although at this time still possibly lateral in origin would be forced into an upright position. Food supply, corolla and ovule development The condition of food supply seems to be an explanation of the abnormalities described here and suggested as reversions. Consideration of the massing of ovaries containing more than one ovule in the centre of the capitula leads to the obvious explanation that being nearer the source of supply from tbe axis the central florets are better nourished and hence have excess food to expend upon ovule production. The true explanation however cannot be so simple as this. Helianthus decapetalus is commonly wild in certain parts of North America (6), and muuifloriis is the commonly cultivated variety(1). Many garden forms grown in good soil are "doubled," while if these are left undivided or are cultivated in poor soil, they revert to the "single" condition. In other words, good nourishment 4-2

11 52 CoMYNs J. A. BERKELEY leads to corolla development, a phr-nomenon that in the family generally is often correlated with sterility of the ovary and in Helianthns in particular is characteristically so. Thus if food supply does control the number of ovules that are produced by the inner florets, the explanation must also take into account the fact that good nourishment also stimulates the outer florets to corolla development. It is suggested that nutrition is one factor controlling both ovule production and corolla development in Helianthus decapetalus, and that it does so in the following manner. In its very early stages the young capitulum consists of a mass of meristem in and behind which there is an accumulation of food, dependent in quantity on the condition of nourishment of the plant as a whole. As the florets arise they draw upon this, and the greater the number that are developing at one time the greater the rate at which the food store will be used. The florets arise in centripetal order. As each successive concentric zone of florets adds its foodconsuming powers to those of the older zones, the general rate of consumption in the inflorescence will increase. The increase in rate will not, however, be maintained, since the younger zones of florets are progressively smaller and the older zones will gradually complete their development, the former leading to progressively smaller increments in the rate of consumption and the latter to gradual decrease in the actual quantity of food consumed. Thus food consumption in the capitulum will tend to follow a curve of the general type shown in Fig. 38, cur\"e A. It does not matter for the purposes of the present argument what the real shape of the curve is, so long as it shows a gradual rise and fall. The one given in Fig. 13 is obtained by assuming that each floret absorbs one food unit during the first unit period of time, two during the next and so on up to four units. After this the rate of absorption is assumed to fall in the reverse manner. The outermost zone of florets is supposed to contain six flowers, each successive zone one less and to commence development one unit time period later than the preceding one. As a consequence of the changing rate of food consumption the quantity' in the capitulum will tend to decrease according to a falling reversed S curve (Fig. 38, curve B), though in reality this curve will be modified by the continuous supply of food entering the inflorescence. It is conceivable that the rate of entry of food would either be constant or else increase gradually as the inflorescence developed. Under either condition the result would be to keep the quantity of food in the capitulum at a more even level during the developmental

12 Abnormalities in Ovaries Ch Developmental._of outermost flor Corollas". yelopmenldl period of ninennost florets n Time Units Fig. 38. Hypothetical curves of food absorption and food residual in capituluni. A. Hypothetical curve of food absorption by developing florets as determined by assuming each floret to absorb at rates increasing from i food unit to 4 per unit time period and then decreasing again to I, the rate changing i food unit per unit time period, the outermost zone of florets

13 54 CoMYNS J. A. BERKELEY period and to give a tendency to increasing quantities both at the beginning and at the end of that period. This tendency to increasing quantity of food would be tbe more marked the greater the initial rate of food entry or tbe greater tbe rate of increase of rate of entry. Curves C i, C 2, C ^ and C 4 (Fig. 38), illustrate tbese points. Turning now to the iiorets we find that the first part to differentiate from the flower rudiment is the corolla ((7), p. 379). At the time when tbis is occurring in the outermost florets there will be a large and possibly increasing quantity of food in tbe capitulum, and tbe outermost Horets are ligulate; moreover it is logical to suppose tbat tbe better a plant is nourished the greater will be the quantity of food accumulated prior to commencement of development and the greater the rate of subsequent supply. Tbese factors tend to maintain tbe food reserves for longer periods in great and increasing quantities, and good nourishment of tbe whole plant leads to "doubling." Thus on account of the ligulate nature of the outer florets and of the occurrence of "doubling" in well-nourisbed plants, it is suggested that large corolla de\'elopment is stimulated by large and increasing food supplies in tbe capitulum at the time when the corollas are differentiating. Tbe ovules are the last parts of the florets to differentiate and by the time they should arise in the outer florets the quantity of food in the capitulum will be smaller and possibly decreasing. Moreover the primordia of large corollas have already been laid down, and it seems feasible to suppose tbat tbese would monopolise the smaller quantity of food available to the detriment of the carpels which would not then be able to produce ovules. On the other hand, florets whose corolla primordia were not laid down till the food in the capitulum was on the wane, would receive no stimulus to large corolla development. Thus, when the time came for ovule formation, the corolla would not compete so severely with the carpels, and these might obtain sufficient food for ovule production. containing 6 florets, each successive zone containing i less and commencing development i time unit later. B. Cur\-e determined from A shomng rate of decrease of residual quantity of initial 400 units of food. C I. B modified by assuming constant supply of food at the rate of 10 units per unit time period. C 2. B modified by assuming constant supply of food at the rate of 20 units per unit time period. C 3. B modified by assuming supply of food commencing at i food unit per unit time period and increasing i food unit per unit time period. C 4. B modified by assuming food supply commencing at 12 food units per unit time period and increasing 2 food units per unit time period.

14 Abnormalities in Ovaries 55 The ovules of the central florets are the last structures in the capitulum to differentiate and, if the plant is well nourished, the food available will again be increasing in quantity. The quantity present and its rate of increase may be sufficient at the time of ovule formation in the central florets to stimulate their carpels to increased activity, even though while their corolla primordia were being laid down it was not in sufficient concentration to stimulate the formation of large corollas. We may imagine here that excess food, together with its increasing quantity, stimulates the only structures still in a sensitive condition the carpels and that these form additional ovules. SUMMARY The structure of abnormal ovaries of Helianthus decapetalus and their distribution in the capitula are described. Suggestions are made that the cordulae may be regarded as the margins of the carpels, the abnormalities as reversions and the ancestral condition one with many parietal ovules. Reasons for upholding Small's view on the relationships of the Compositae are stated in so far as this research bears upon them. Suggestions are made as to the origin of the upright condition of the ovule in the Compositae and as to the reason for the abnormal ovaries found. REFERENCES (1) BAILEY, L. H. The Standard Cyclopedia of Horticuttuve, ^ (2) BROWN, R. Some observations on the natural family of plants called Compositae. Trans. Linn. Soc. 12, (3) COULTER, J. M. and CHAMBERLAIN, C. J. Morphology of Angiosperms, p (4) DON, D. An attempt at a new classification of the Cichoriae. Edin. New Pint. Journ. 6, 305. i82g. (5) On the origin of the ligulate rays in Zinnia. Trans. Linn. Soc. 16, (6) GRAY, A. Synoptical Flora of North America, ed. 2, p. 2S (7) GoEBEL, K. Outlines of Classification and Special Morphology, pp. 378, 379, (8) RENDLE, A. B. Classification of Flowering Plants. Vol. 11, p (9) ScHWERE, S. Zur Entwickelungsgeschichte der Frucht von Taraxacum officinale. Flora, 82, (10) SMALL, J. Anomalies in the ovary of Senecio vulgatis. Ann. Bot. 30, (11) Origin of the Compositae. New Phyt. Reprint, 11,-p. 2T,J{ (12) VAN TIEGHEM, P. L'Oeuf des Plantes. Ann. Sci. Nat. Bot. ser. 8, 14, (13) WARMING, E. and POTTER, B. C. Systematic Botany, p (14) Observations sur la Valeur Systematique de l'ovule. Mindeskrift /. Japet. Steenst

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