AESTIVATION IN RANUNCULUS REPENS L.

Transcription

1 ESTVTON N RNUNCULUS REENS L. BY G. J. CUNNELL Birkbeck College, University of London {Received September 1) (With figures in the text) SUMMRY The aestivation of the caljrx and corolla in mature flower buds of Ranunculus repens from tvo sites near London is recorded. Only two forms of quincuncial arrangement of the are found and in almost equal numbers. One form is the mirror-image of the other and they continue the spiral from the prophylls in the left or right direction respectively. ll thirty-two possible arrangements of the corolla are found in both samples but their frequencies are very unequally distributed. There are more quincuncial and less apotactous and convolute forms than is expected by chance alone. t the three posterior positions the two possible overlaps are more or less equally frequent overall, but there is a high correlation between the type of calyic and direction of the overlap. The predominating overlap is the eutopic one, i.e. the overlap at each position found in the corolla arrangement which continues the f spiral from the caly^x. Overlaps involving the anterior petal appear to be entirely due to chance although in the site sample there is a significant tendency to metatopy where the anterior and right lateral petals overlap. These observations are compared with published work on aestivation in other species with variably imbricate pentamerous corollas and their significance is briefly discussed. METHODS n June 1 over mature lateral flower buds of Ranunculus repens were collected from each of two sites about \ mile apart near Hampstead, London. large number of plants of the species were present at each site and the lateral flower buds were collected randomly and preserved in per cent alcohol. Three hundred and twenty buds from each site were carefully dissected under a binocular microscope. Only pentamerous flowers were recorded, all those with less or more than five sepals or petals being rejected. The few flowers in which reversal of the overlap at one or more points occurred were also rejected. Great importance was attached to orientating the flower correctly and identifying the posterior sepal. This was done by following a ridge or groove on the posterior side of the pedicel up from its insertion in the axil of the subtending bract to the base of the flower. Eurther, the two prophylls are not inserted opposite each other but in such a way that the smaller angle between them is on the posterior side of the pedicel (Eig. i). fter a little experience correct orientation became a simple matter even when the pedicel was twisted. The sepals were bent back and the closely packed petals gently teased apart.

2 estivation in Ranunculus repens L. 1 s well as having primary contact with its immediate neighbours each petal also extends round and over the bud to overlap or be overlapped by the other two petals. Only the primary overlaps resulting from first contacts of the developing petals are considered in this investigation. Fig.. Diagrams of mature flower bud of Ranunculus repens to show orientation,, posterior view; B, lateral view; C, view from abo\e. a, inflorescence axis; b, subtending bract; p, pedicel; pr, prophyll; s, posterior sepal. TERMNOLOGY n the literature on aestivation a great deal of confusion has resulted from the use of different terms for the main types of arrangement and from different uses of the same term by various authors. This has been discussed at length by Gray (1), Henslow (), Church (1), Schoute (1) and many others. However, in this paper propose to use the terms suggested by Riley (1) who studied aestivation in Ranunciihts bitlbosus and R. acris. The four main types are: 1. Oitinciincial. Here, two petals are wholly outside, two are wholly inside and the other petal has one edge overlapping and the other overlapped (e.g. Fig., type i). This arrangement corresponds to a % spiral.. aratactous. Only one petal is wholly outside and one wholly inside, these two petals being adjacent to each other. The other three petals are half overlapped (e.g. Fig., type ).. potactotts. This is similar to the paratactous type but the outside petal is not adjacent to the one wholly inside (e.g. Fig., type ).. Convolute. Here each of the ffve petals has one edge outside and the other overlapped (e.g. Fig,, type ). t each of the ffve points of overlap there are two possible arrangements. Therefore, as Church (1) has pointed out, there are a'^ = possible configurations of the pentamerous corolla. These are all illustrated and numbered for reference in Fig,, From this it can be seen that there are quincuncial types, paratactous, apotactous and convolute. Schoute (1 s) pointed out that of these thirty-two types there are two, one being the mirror-image of the other, in which both and corolla are quincuncial and in which the spiral can be followed without interruption or reversal from the subtending bract, via the prophylls and sepals and through the corolla (Fig. ). These he termed eutopic.

3 G. J. CuNNELL Fig.. Diagrams of the possible arrangements of the petals of a pentamerous corolla., quincuncial;, paratactous;, apotactous; C, convolute.

4 estivation in Ranunculus repens L. The members of the floral envelopes are numbered from i-io in the sequence of the spiral in each type. From above one has a right and the other a left spiral and they are named as such in this work. This follows traditional practice although Schoute himself adopted the reverse definition. The right eutopic corolla is type i of Fig. and the left eutopic corolla is type of Fig.. ll the other types Schoute termed metatopic. f the caljrx is stable then the degree of metatopy is variable in the different corolla types. For example, if type i. Fig. is eutopic then type, which differs from it in only one position, can be described as - eutopic and type, which differs from it in all five positions, is g eutopic, i.e. completely metatopic. THE CLYX This is remarkably stable and only two types were found. They are both quincuncial with the posterior sepal overlapping at both edges. One is the mirror image of the other and they continue the spiral from the prophylls in the left and right direction respectively (Fig. ). Fig.. Diagrams of the floral envelopes of the two possible types of eutopic pentamerous flowers., right eutopic; B, left eutopic; b, subtending bract; a, p, prophylls; 1-, sepals and -, petals, numbered in the f spiral sequence. The occurrence of the two types appears to be entirely due to chance. The first flower in an inflorescence may have a right or left and the later flowers do not follow any recognizable sequence of the two types. This is supported by an analysis of the dissected flowers. n neither site do the numbers of the two types differ significantly (Table i). Table. numbersof types Right Left X- Site Site O Once the constancy of the was established the arrangement of the sepals provided further guide to the orientation of the flower. lthough in each type there are two

5 G. J. CUNNELL sepals outside at both edges it is only the posterior one which has the two adjacent ones entirely inside. Thus the posterior sepal can be easily identified and the flower correctly orientated. THE COROLL The first stage in the analysis was to determine the frequency of the four main corolla types at each site (Table ). Table. Main corolla types at each site Expected frequency at each site Site Frequency X^ Site a Frequency X- uincuncial aratactous. los.s potactous.. Convolute.. -. t both sites = <o.ooi and therefore the frequencies differ significantly from those expected on the theory that all thirty-two configurations are equally likely. t is clear from Table that the quincuncial type occurs more frequently than expected. With the small exception of the paratactous type in site the other types are not as common as expected. This does not take into account either the distribution of corolla types within the four groups or the relationship, if any, with the. The frequencies of the thirty-two corolla types with left or right calyces in both sites are given in Table. Several points emerge from an inspection of this table. There is a general similarity between the two sites and all thirty-two possible types of corolla were found at both of them. f the types were equally likely to occur a fairly even distribution would be expected. However, this is obviously not so, as. per cent fall in the types 1-. Six of these eight are quincuncial and are responsible, in part, for the overweighting of this group indicated in Table. t is also noticeable that the quincuncial types 1 and are well represented. still more striking point concerns the distribution of the corolla types within the two types. Of the total of 1 flowers with corolla types 1-, 1 had a right and only 1 had a left. With the corolla types - the reverse is found. Here 1 flowers had a left and only a right. Thus, although the two types of are almost equally represented in each sample, they are very unequally distributed among the corolla types. This analysis may be carried further by applying the method used by Schoute (1). Corolla type i is eutopic for the right and corolla type is eutopic for the left. Therefore, within each type each possible corolla arrangement can be designated by the number of eutopic overlaps it shows.

6 estivation in Ranunculus repens L. Table. Frequencies of all possible and corolla types found at each site Site Site Both sites Corolla no.* Corolla type Right Left Right Left Right Left C C ^^ quincuncial; = paratactous; ^= apotactous; C ^ convolute. * s shown in Fig., Table. Frequencies of corollas shozving different degrees of etttopy Site bite expected frequency at each site Right Left Right cau'x Left calvx Eutopic 1 1! % Eutopic Eutopic o.i 1. f Eutopic! - 1. i Eutopic Metatopic 1,) jj 1 1 J!. 1,

7 G. J. CUNNELL For each site Table shows the frequencies expected, if randomly distributed, of the six possible categories from complete eutopy to complete metatopy and the figures actually obtained. t is clear that there is a significant departure from the expected frequency at both sites ( = <o.ooi). n fact there is a marked tendency for eutopy to occur at the expense of metatopy as can be seen from the line diagram of Fig.. = Expecled frequency = Observed frequency Site ]? = Observed frequency Site E Europic 'i Eutopic ' V Eutopic ' - Eufopic ' " Eutopic Fig.. Frequencies of flowers with different degrees of eutopy. Metatopic Overall there are three and a half times as many completely eutopic flowers as expected and less than one-third of the expected number of metatopic flowers. There are less -J and eutopic flowers and more eutopic flowers than expected. t is only at the central eutopic position that the sites differ slightly, site i having more and site less than expected. Table. number of eutopic and metatopic overlaps expected frequency at each site Right Left Site X" Right Left Site X^ Eutopic overlaps Metatopic overlaps

8 estivation in Ranunculus repens L. The extent of eutopy can be further illustrated by calculating the total number of eutopic and metatopic overlaps at each site. Table clearly shows this preponderance of eutopy in flowers with both types of at both sites ( = <o.ooi). Of the total of overlaps in the flowers examined 1 were eutopic and 1 metatopic. However, this does not give any information about the distribution of eutopy at the five points of overlap. The data set out in Table provide the first step to determine this. The frequency of the two possible types of overlap at each of the five positions is given for the flowers of each type at each site. Table. Frequencies of the two possible arrangements at each of the five overlap positions Site Site Right Left Right Left Rt T T * R X^ p O T,* T,T, LLf L x' p <o.ooi Rt RL RT * R X^ p 1-1 ". <o.ooi 1 1.l O.O-O.OO LL 1 1 *t LT, O.O O.O O..-. RL *t RL O.O R = right posterior petal. L = left posterior petal. RL = right lateral petal. LL = left lateral petal. = anterior petal. * Overlaps eutopic for flower with right. t Overlaps eutopic for flower with left. The only overlap on the median plane is that between the two posterior petals. t neither of the sites is there a significant difference between the total number of right

9 G.J. CUNNELL posterior over left posterior overlaps and the total number of left posterior over right posterior overlaps. When, however, the type of is taken into account a strikmg difl'erence is found. t both sites, of the flowers with a left about three times as many have the right posterior over left posterior overlap as have the left posterior over right posterior overlap. Conversely, of the flowers with a right about three times as many have the left posterior over right posterior as have the reverse overlap. Thus to a great extent the overlap between the two posterior petals 'follows the ' and the important point here is that the predominating petal overlap is the eutopic one. The right posterior over left posterior petal overlap is eutopic with a left and is far more common in flowers with this type of. Conversely, in flowers with a right the eutopic left posterior over right posterior petal overlap predominates. very similar situation is found where the left posterior and left lateral petals overlap. t both sites there is a highly signiflcant preponderance of left posterior over left lateral petal overlaps in flowers with a right and left lateral over left posterior petals in flowers with a left. Here again these are the eutopic combinations. Though not statistically signiflcant there are more left posterior over left lateral petals than vice versa in the site i sample but the reverse is true for the site flowers. Taking the two sites together the two overlaps are almost equally represented (1 left posterior over left lateral, left lateral over left posterior). gain, the overlaps between the right posterior and right lateral petals have this relationship with the ahhough the difference between the frequencies in the flowers with a left at site is only signiflcant at the = o.oi level. This causes a signiflcant difference between the total frequencies of the two types at site with the right lateral over right posterior petal arrangement being more common. n contrast, the relationship between the anterior petal and the two lateral ones is rather different. s with the other points of overlap there is no signiflcant difference between the total number of left lateral over anterior and anterior over left lateral overlaps. Neither is there a signiflcant difference between the frequencies of these overlaps in flowers with a right or left. Thus it appears that the type of overlap found at this position is entirely due to chance and cannot be related to the type. Table. Distribution of eiitop] ' and metatopy at the five points of overlap Site Site osition Eutopic Metatopic Eutopic Metatopic X" < < O.O-O.OO 11 1 O.O.-. The same kind of thing is found in the site sample where the anterior and right lateral petals overlap. However, at site i the flowers with a left have a highly signiflcant preponderance of right lateral over anterior petal overlaps which also makes the totals signiflcantly different.

10 estivation in Ranunculus repens L. n both right and left eutopic corolla configurations the anterior petal has both its edges outside (Fig. ). Thus from the data of Table it appears that eutopy and metatopy are equally likely to occur between the anterior and left lateral petals but that metatopy is more common in site i fiowers (although not in site fiowers) where the anterior and right lateral petals overlap. To determine the degree of eutopy at the points of overlap in each sample as a whole it is necessary to combine the data for the right and left types in each sample. For convenience the petals are numbered - in the spiral sequence (Fig. ). To get a single figure for the - position the data for the overlaps between the anterior and right lateral petals of flowers with a right are combined with those for the overlaps between the anterior and left lateral petals of fiowers with a left. The other four positions are treated similarly giving the figures shown in Table for eutopic and metatopic overlaps in each of the five positions at each site. Observed = frequency Site 1 Number of Eutopic overlaps Number ol Metalopic overlaps pjg ^ Frequencies of eutopy and metatopy found at each of the five points of overlap. t is quite clear from Table and from Fig. that there is a significant tendency to eutopy in the three posterior points of overlap -, - and -. t the two anterior points of overlap there is no such tendency. t the - position overlap appears to be entirely due to chance and although there is a slight tendency to metatopy at the - position at site i the average of the two sites is not significantly different from that expected from random overlapping.

11 O G. J. CUNNELL DSCUSSON fter preliminary observations which showed that the aestivation in flowers of Ranunculus repens L. was variable the main object of this investigation has developed. That is, to examine a sufiiciently large sample at two sites in order to obtain some idea of the type and extent of this variability. s far as can be discovered from the literature, aestivation in this species has not been investigated previously. However, there are several papers dealing with other species of Ranunculus and the data in these may be usefully compared with mine. Henslow () gives the following percentages for the fiowers of R. bulbosus. Right quincuncial per cent\ ^^ uincuncial per cent Left quincuncial 1 per cent / Right imbricate 1 per cent\ i.e. aratactous per cent ' Left imbricate 1 per cent J Right imbricate per cent\ ^_^_ potactous 1 per cent Left imbricate per cent J Right convolute per cent\.^ Convolute 1 per cent Left convolute per cent f The author makes no comment on these figures and does not indicate how they were obtained. t is clear, however, that the quincuncial type is over-represented and the apotactous type under-represented when compared with the 1. per cent expected if the aestivation was due to chance alone. The percentage of convolute fiowers is twice that expected (. per cent). Henslow makes no mention of the and therefore no further comparison with my data is possible. Riley (1) examined many fiowers oi R. acris [R. acer) and R. bulbosus. summary of his figures is as follows: R. bitlbosus ( fiowers) R. acris ( fiowers) uincuncial. per cent. per cent aratactous 1. per cent.1 per cent potactous. per cent. per cent Convolute. per cent. per cent He declares that the percentages of the four phases are such as might be expected were the direction of the overlap of the petals purely fortuitous. However, he does not take into consideration the large size of his sample. t is true that the percentages of the types in the R. btdbosus sample do not differ significantly from those expected by pure chance (x" =.) but if the frequency of the totals are compared X" = - which is significant at the =. level. gain it is the quincuncial form which is over-represented and the apotactous form under-represented. The totals for the sample of R. acrisfiowersdo not suggest that the aestivation is not purely due to chance (x" =.) (for d.f =, =., X" = -). He states that, for both species, the is normally quincuncial, only one out of fiowers of R. bulbosus having an apotactous arrangement. He could find no relationship between the direction of overlap of sepals and petals although he notes that the homodromous and antidromous arrangements are equally frequent. Evidently he did not record the orientation of the corolla so that further analysis of his data into the thirty-two forms is not possible. Schoute (1) in a long paper, which surveys the whole problem of aestivation, deals

12 estivation in Ranunculus repens L. 1 with three Ranunculus spp. all of which have variably imbricate corollas. Of flowers of R. lingua he flnds quincuncial, apotactous, paratactous and mixed.* This suggests a chance distribution but the number of metatopic overlaps at each position are - (i), - {bl), - (i), - (io-i), - (i), giving a total of metatopic and eutopic overlaps. Thus there is a strong tendency to eutopy at all flve points of overlap. He examined flowers of i?. acris and found 1 quincuncial, apotactous, 1 paratactous, convolute and mixed. The metatopic overlaps were - ( i), - (), - (1), - (), and - (), giving a total of io metatopic and 1^ eutopic overlaps. This species therefore diflers from R. lingua in that there is no tendency to eutopy and that overlapping at all flve points is apparently due to chance. Fifty flowers of R.flammula gave very similar results with io metatopic against i eutopic overlaps. My data suggest that R. repens differs from the above species and falls between them. There is a signiffcant preponderance of quincuncial types and, as in R. lingua, eutopic overlaps are far more common. However, these are not equally distributed, the three posterior points of overlap -, - and - showing a marked tendency to eutopy whereas at the two anterior points (with the exception of some metatopy at the - position in the site i sample) overlap appears to be due to chance. Schoute deals with three species in the group with a marked tendency to eutopy which is weakened or altogether absent at one or more edges. For example, of flowers of Rosa canina 1 were quincuncial, apotactous, paratactous, i convolute and i partly open. Metatopies were - (), -io (ii), - (), - () and - (), giving a total of metatopic overlaps and ^ eutopic overlaps. Here there is a strong tendency to eutopy at four points but it is absent at the - position. So far in this investigation facts alone have been recorded and no attempt has been made to deduce anything from them. Riley (1) concludes from his data that the apparently fortuitous overlapping of the petals indicates that they are cyclically and not spirally arranged. The sepals are spirally arranged and he puts forward these points to support the idea that the sepals were derived from bracts and the petals from stamens. However, as the stamens themselves are spirally arranged (Tepfer, 1) this viewpoint seems to be untenable. Schoute (1) claims that the corolla in Ranunculus has a spiral origin, a fact which he states has been fully conflrmed again by the researches of Hirmer and of Schoffel (against this Riley refers to the earlier work of ayer which indicated that the primordia of the petals arise simultaneously). However, in two of the three species investigated by him there is no trace left in the older ffowers of the spiral origin of the petals. Further, Tepfer (1) states that in R. repens the flve petals are formed simultaneously soon after the last sepal is initiated. n R. repens it appears that the spiral origin, if any, has been obscured in the anterior part of the flower but not in the posterior part. Whether the primordia arise successively or simultaneously the fact remains that in the developing flower bud the petals grow slowly and are for some time not in contact with each other. s they expand they push between the enfolding and the large anthers of the outer stamens. t is diflicult to see how the growth rates of the petals, even if they are different, can greatly affect the subsequent overlapping when the edges come in contact. t the stage when the petals flrst come in contact with each other the bud is small and the pedicel is extremely short. The flower is enclosed on its anterior side by the curved * Le. with one or more edges open or different at different levels. These he records as s when determining the numher of overlaps.

13 G. J. CUNNELL base of the large subtending bract. t is possible that pressure on the anterior side may in some way affect the overlapping of the anterior petal. The two prophylls are much smaller than the bract and are positioned more towards the posterior side of the flower and do not seem to have any effect on the aestivation. Whatever may be the operative factors the variability of the corolla aestivation is clearly estabhshed. Further, the observations show, without doubt, that the distribution of overlaps is not random and can be related to the two types. w ish to thank rofessor C. T. ngold for his interest in this work and for critically reading the manuscript. REFERENCES CHURCH,, H, (1), Types of floral mechanism,. Oxford. GRY,. (1). estivation and its terminology. mer. J. Sci., rd Ser,,,. HENSLOW, G. (). On the origin of Boral aestivations. With notes on the structure ofthe Cruciferous flower, on that of doxa, and on the corolla ol rimula. Trans. Linn. Soc. Lond. {Bot.), nd Ser., i, 1- RLEY, L,, M, (1), Variable aestivation of Ranunculus bulbosus and R. acer. J. Bot. Lond., 1,. SCHOUTE, J, C, (1), On corolla aestivation and phyllotaxis of floral phyllomes, Verh. kad. Wet. mst. fd. Natuurkunde (b),, No,, i, TEFER, S,.S. (1). Floral anatomy and ontogeny in qiiilegia formosa var, truncata and Ranunculus repens. Univ. Calif. iibl. Bot.,, 1.

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