Primula Elatior Jacquin: Its Distribution in Britain Author(S): Miller Christy Source: Journal of Ecology, Vol

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Primula Elatior Jacquin: Its Distribution in Britain Author(s): Miller Christy Source: Journal of Ecology, Vol. 10, No. 2 (Nov., 1922), pp. 200-210 Published by: British Ecological Society Stable URL: http://www.jstor.org/stable/2255741 Accessed: 27-06-2016 10:58 UTC

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PRIJIMULA ELATIOR JACQUIN: ITS DISTRIBUTION IN BRITAIN

BY MILLER CHRISTY.

(With Map: Plate XVIII.)

In 1897, in a lengthy paper on " Primula elatior in Britain-'," I defined, with considerable exactitude, the highly-remarkable distribution in this country of this particularly-interesting species2 -the "True" or "Bardfield" Oxlip, so long overlooked in Britain, because it was confused here with the much more widespread and somewhat-similar, but quite distinct, hybrid between the Cowslip and the Primrose (P. veris x vulgaris). In the paper referred to, I showed that the plant, though wide-spread on the Continent, is, in Britain, confined (apart from a couple of very small outlying localities) to two "Districts" (as I called them), forming a single "Area," within which it grows, in immense abundance, in all old woods and, exceptionally, in small numbers, in boggy meadows beside streams. The two Districts may be defined as follows3: (1) a large eastern District, with an extremely irregular outline, covering some 475 square miles in area, and lying mainly in the counties of Essex and Suffolk, but extending a little way into Cambridgeshire and to a minute extent into Hertfordshire; and (2) a much smaller western District, roughly triangular in outline, extending to some 45 square miles in area, and lying mainly in Cambridgeshire4, but extending a little way into Huntingdonshire5. These two Districts are separated from one another, as I showed, by a broad gap, varying from 15 to 20 miles wide, formed by the valley of the River Cam. I showed also that both Districts lie entirely upon the Chalky Boulder Clay6. I Journ. Linn. Soc. Bot. 33 (1897), pp. 172-201, and map. 2 I had previously defined its range in the county of Essex (see Trans. Essex Field Club, 3, 1884, pp. 172-178, and map). 3 They were shown very clearly on the map accompanying my paper above mentioned and reproduced here with modifications and additions (P1. XVIII). 4 It seems probable (see post, p. 208 n.) that, two or three centuries ago, this District covered a slightly larger portion of Cambridgeshire than it does now. 5 The Oxlip Area extends (it will be found) to six of Watson's 112 counties and " vice-counties" (namely, Nos. 19, 20, 26, 27, 29, and 31), instead of the four Watson mentions (Topogr. Bot. p. 334, 1883), one of which (No. 30, Bedfordshire), I reject through lack of evidence as to the occurrence of the plant therein. 6 I am greatly indebted to Mr William Whitaker, F.R.S., for assistance in tracing the intimate connection between the Oxlip and the Boulder Clay.

This content downloaded from 130.63.180.147 on Mon, 27 Jun 2016 10:58:34 UTC All use subject to http://about.jstor.org/terms JOURNAL OF ECOLOGY VOL. X, PLATE XVI I 1.

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The Oxlip is, indeed, strongly calciphilous, and never grows upon a non- calcareous soil-at least, not in Britain. In the small western District, says Mr Adamson', it is even absent from those patches of the Boulder Clay from which the lime has been leached out, leaving it a mere loam. The plant requires also a high degree of moisture, such as it finds in abundance in the Boulder Clay2. Yet, as I have often observed, it avoids the chalk wherever it is not overlain by the Boulder Clay, probably because the surface of the chalk has not a sufficiently high water-content for its requirements. I showed, further, that the two Oxlip Districts occupy only the highest and most unbroken portions of the Boulder Clay. Of the large eastern District, no part lies, I believe, below 275 feet, while the highest part (that near Depden and Wickhambrook) rises to just over 400 feet-a considerable elevation for the Eastern Counties. The smaller western Oxlip District occupies almost completely an isolated patch of Boulder Clay, lying between the valleys of the Cam and the Ouse, and having a lesser elevation-from about 150 feet up to about 250 feet. Nowhere (except in certain outlying localities to be mentioned hereafter) does the plant descend much below these levels; nor does it occupy the low gravelly valleys of the rivers running out of these stretches of high ground-a fact which accounts for the deep indentations already mentioned in the margins of the large eastern District; while, as stated, the large, low-lying valley of the Cam actually divides the Oxlip Area into its two Districts. The close relationship between the Oxlip and the Boulder Clay is shown clearly by the accompanying map. How exceptionally elevated these Oxlip Districts are, as compared with the country surrounding them, may be gathered from the large number of streams which rise within them and flow out in all directions. Several considerable streams have their sources within the very small western District; while most of the principal rivers of East Anglia rise within the much larger (but still comparatively small) eastern District; and these flow out of it on all its four sides, as follows: on the north, the Kennet, the Lark, and a tributary of the Little Ouse; on the east, the Gipping, the Brett, the Stour, and the Colne; on the south, the Pant, the Ter, the Chelmer, the Roding, and the Stort; and, on the west, the Granta. In regard to the plant itself, I showed that: (a) both the Districts forming the Oxlip Area are very sharply defined; that, (b) within its Area, the plant grows everywhere (that is, of course, in all suitable habitats) in immense abundance. Equally remarkable is the fact that, 1 Trans. Bot. Soc. Edinb. 24 (1912), p. 85. 2 Mr Adamson says (op. cit. p. 84) that, in the Oxlip Woods in the small western District, the Boulder Clay has a lime-content sometimes slightly exceeding 7 per cent., with an average of about 4 per cent.; that it becomes in winter super-saturated, the " water-content never falling much below 30 per cent. at any time of the year"; also that the Oxlip ceases to flourish on it where its water- content falls much below 25 per cent.

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(c) while the Primrose grows abundantly all round the Oxlip Area, it is (through causes suggested hereafter) entirely absent from that Area; but that, (d) all round the boundary of that Area, where the two species come into contact, they produce hybrids in great abundance (except along one short stretch, where exceptional conditions prevail). On the other hand, (e) the Cowslip grows abundantly, not only all round, but also throughout the whole Oxlip area; yet (f) these two species, though everywhere in contact with one another, hybridize very rarely1. In regard to the two outlying localities for P. elatior, referred to above: these were (1) a very small group of plants in a wood at Great Livermere, in Suffolk, and (2) an equally-small patch at Dickleburgh, in Norfolk2. It is a matter of some gratification to me that, in the 25 years which have elapsed since the appearance of my paper, no one has seriously called in question (so far as I know) either the facts I recorded or the conclusions I expressed; nor has anyone succeeded in extending, to any appreciable degree (so far as I know) the boundaries of either of the two Districts I defined. The publication of my paper has, however, led to the discovery of several new outlying localities for the plant and to the acquisition of additional information in regard to the two I noted. The outliers (ten in number) now known to exist are of considerable interest; and my chief object in the present paper is to place on record what I have been able to ascertain in regard to them. They are indicated by means of red dots on the accompanying map. All are in the county of Suffolk, with the exception of that (already mentioned) in Norfolk; and all lie within an extension of the Boulder Clay which exists to the north and north-east of the eastern Oxlip District (that is, between the valleys of the Rivers Lark and Gipping on the south and that of the Little Ouse on the north)3. This extension of the Boulder Clay lies almost everywhere at a considerably lower elevation than that which it reaches within the Oxlip Area. Indeed, some of 1 Much information in regard to the hybrids produced between our three common British species of Primula was given in my paper above mentioned. Further information in regard to them may be found in a paper I am contributing to a forthcoming number of The New Phytologist. 2 The information given above is recapitulated for convenience, inasmuch as my paper is now out of print and practically unobtainable. 3 I do not say that all the Oxlips growing in these outliers are actually rooted in the Boulder Clay itself; for they are not. Many of the plants grow (as the following will show) in damp peaty alluvium beside small streams. But all the outliers are within the area which the Drift Maps of the Geological Survey indicate as Boulder Clay; and, in the case of all, that deposit must exist no more than a few feet below the surface; or, if it lies deeper than that, there is very likely present a deposit of calc-tufa (derived from the Boulder Clay) which often lies just below the peaty alluvium in the bottoms of the valleys of those of our East Anglian streams which flow off the Boulder Clay. Some of these Oxlip outliers lie, however, only just within the Boulder Clay area -one, at least, of them only a few yards within it; while another is situate on a very small outlier of Boulder Clay. There is not in Britain (so far as I know) a single Oxlip plant growing off the Boulder Clay.

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the outlying localities have an elevation of scarcely 50 feet, and one only lies above 200 feet. A peculiarity of these outlying localities for the plant is that most of them are in the open, chiefly in damp boggy meadows beside streams; whereas, within the Oxlip Area proper, a vast majority of the plants grow in woods'. The outliers (taking them in order as one passes from east to west) are: (1) At Tuddenham, at a spot about 4- miles north from the nearest point on the margin of the Oxlip District, and situated, at an elevation of about 50 feet only, within a tiny outlying patch of Boulder Clay not shown on the map through an unfortunate oversight. Here a few plants grow in a small and very swampy strip of wood, through which runs a stream, just below the village. The locality was discovered on 7 April, 1912, by Dr C. E. Moss and myself, as a result of information supplied to me by Miss F. P. Goddard, late of East Dereham, Norfolk, to the effect that she had found Oxlips of some kind growing there. (2) At Cavenham, at a spot two miles east from Tuddenham, about five miles north from the nearest point on the margin of the Oxlip Area, at an elevation of about 50 feet, and situated on the extreme margin of the Boulder Clay area. Here, in a small, damp, boggy meadow, surrounded by bushes and trees (chiefly alders and willows), on the very bank of a small tributary of the River Lark, are several patches of Oxlip plants (perhaps 30 altogether), inter- mixed with a few Cowslips and several hybrids between them. The locality was discovered, on or about 5 May, 1911, by a party led by Dr C. E. Moss, and comprising the late Rev. E. S. Marshall, Mr R. S. Adamson, and Mr A. J. Wilmott. I visited it in company with Dr Moss on 7 April, 1912. (3) At Westley, at a spot about five miles south-east from the Cavenham locality, about one mile only from the nearest point on the margin of the Oxlip Area, at an elevation of a trifle over 200 feet, and only just within the extreme margin of the Boulder Clay area in this direction. Here, near the eastern end of Old Warren Wood, on 14 April, 1911, Mr Guy Maynard, Mr George Morris, and myself, discovered a small patch of plants (probably less than a dozen) among many Primroses, having been directed to them by the game-keeper, who had noticed that they were different from the Primroses around them. (4) At Fornham, at a spot on the bank of the River Lark, about five miles east from Cavenham, about four miles from the nearest point on the margin of the Oxlip Area, at an elevation of rather less than 100 feet, and on the Boulder Clay, which here comes down to the very bank of the river. Here the Oxlip grows (or grew formerly) in some abundance, in the damp riverside meadows, as I am informed by Mr Henry Miller, of Ipswich, who remembers seeing it there many years ago. Skemner also reported it2 from (apparentlv) the same locality. ' I observed long since (op. cit. pp. 199-200) that, wherever the plant grows in the open within the Oxlip Area, it always does so in boggy meadows beside streams, and generally, if not always, at the points at which these streams leave the Oxlip Area-that is to say, near the heads of the deeper indentations formed by their valleys in the margin of that Area. 2 See Hind's Flora of Suffolk, p. 282 (1889).

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(5) At Great Livermere, at a spot about four miles north-east from Fornham, about six miles north-east from the nearest point on the margin of the Oxlip Area, and situated on the Boulder Clay, at an elevation of about 200 feet. Here, in April 1896, when in company with Mr J. C. Shenstone, F.L.S., I discovered, in a sloping wood known as "the Thicks," a small patch of Oxlip plants (perhaps no more than half a dozen) growing among numerous plants of the Primrose. This wood was afterwards visited and more fully searched by Mr (now Capt.) A. W. Hill, F.R.S., who saw in it many more Oxlips than I did. He says1 that, while Primroses occupy the higher southern end and the margins, the lower northern end (elevation about 200 feet) is occupied by Oxlips, Cowslips and numerous Oxlip-Primrose hybrids (P. elatior x vulgaris); also that, on 26 April, 1906, he found among these, growing beside a broad ride through the wood, a single large plant of the rare Oxlip-Cowslip hybrid (P. elatior x veris), of which he gives a good description and a very excellent figure. (6) At Great Livermere, at a spot about three miles north-east from Fornham, about five miles north-east from the nearest point on the margin of the Oxlip Area, and situate on the Boulder Clay, at an elevation of about 110 feet. Here, on 26 April, 1906, Capt. Hill discovered a patch of plants (the second in this parish) growing in a boggy spot, partly overgrown with bushes, on the edge of the lake in Livermere Park2. (7) At Tostock, at a spot about six miles south-east from Livermere, about one mile north from the nearest point on the margin of the Oxlip Area, situate on the Boulder Clay, and at an elevation of about 10 feet. For my knowledge of this outlier, I am indebted to the Rev. Julian G. Tuck, rector of the parish, who, when sending me undoubted specimens on 22 May, 1922, wrote: " This is the flower I have known as the Oxlip for quite 60 years. It grows in abundance in one field [a meadow] here and, I believe, in several places near; but I have never searched for it, knowing always where to find it near our church when it is wanted. Our children call it 'Five-fingers3.' 5 This locality (and any others in the parish) are in low meadows near the small stream (? nameless) which runs through Tostock northwards, joining the Little Ouse about 10 miles further north4.

1 New Phytologist, 6 (1907), pp. 162-166. 2 Capt. Hill informs me that he has not visited Livermere since the date indicated, so can give no additional information. This is the Oxlip's popular name wherever it grows in Suffolk. It seems, at first, particularly inappropriate; for the flowers of the plant bear no sort of resemblance to the fingers of the human hand when these are held fully extended and spread, as one usually thinks of them. If, however, the forearm be held upright and the hand bent over sharply at the wrist, with the fingers relaxed and slightly spread, the resemblance of the umbel of the Oxlip, with its characteristic one-sided droop, to the human hand becomes strikingly obvious. 4 Hind's Herbarium at Ipswich (see post, p. 205) contains a specimen, collected by him at Tostock on 27 April, 1891, which, though wrongly identified, appears to be a small meadow-grown example Qf the True Oxlip.

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(8) At Honington, at a spot slightly further north than any of the foregoing, about eight miles north from the nearest point on the margin of the Oxlip Area, situate on the Boulder Clay, and at an elevation of about 75 feet. The Rev. W. M. Hind, though long rector of this place, clearly had not recognized it as a locality for the True Oxlip at the time (1889) when he published his Flora of Suffolk; for he does not mention it as such. Yet, very soon after that, he must have recognized the plant as occurring there; for his Herbarium, now in the Ipswich Museum', contains, among several doubtful specimens from the parish, at least two, collected there by himself, on 13 May, 1889, and 30 April, 1890, respectively, which were correctly identified and labelled by him. Doubt- less, the precise locality from which they came was some low, damp, stream-side meadow. (9) At Gipping, at a spot eight miles east from Tostock, about three miles north-east from the nearest point on the margin of the Oxlip Area, and situate on the Boulder Clay, at an elevation of about 135 feet. For my knowledge of this outlier, I am indebted to Mr Arthur Mayfield, F.L.S., of Mendlesham, who has kindly searched the parish and has sent me undoubted specimens from the Great Wood, the Little Wood, and the Grove, in all of which the Oxlip is abundant and there are no Primroses. All these lie quite near a small stream which, rising in the adjoining parish of Mendlesham (where there are plenty of Primroses, but no Oxlips), forms one of the sources of the River Gipping. (10) At Dickleburgh, Norfolk, at a spot about 16 miles north-east from the nearest point on the margin of the Oxlip Area, and situated on Boulder Clay, at an elevation of about 90 feet. Here a very limited number of plants occurs at a certain spot of very limited extent in "the Moor," a low boggy flat in the valley of a small tributary of the River Waveney. This outlier is certainly, in every respect, the most interesting of all. Not only was it the earliest recorded, but it is the most limited in extent, and it is situated at a far greater distance from the Oxlip Area than any of the others. It is confined to a small hummock, oval in shape, perhaps 150 square yards in extent, rising two feet and a half or three feet above the level of the surrounding meadow-land, which is swampy and frequently flooded in winter, producing Caltha palustris in abundance. The hummock itself is of a peaty soil, always remains spongy and wet (even when the surrounding meadow-land is dry in summer), and is covered with a species of Carex2. The first to call attention to this outlier was Miss A. R. Smith, of Dickleburgh, to whose family the fact that Oxlips grew there had been known since the " Forties " of last century. Specimens supplied by her to the Rev. F. W. (now Canon) Galpin in 1886, and carefully verified by him, enabled him, after personally visiting the locality, to record it soon

1 This was mislaid when I wrote in 1897 (op. cit. p. 187), but has recently come to light, and I have been afforded an opportunity of going through it carefully. 2 J believe the hummock to be either an old beaver-dam or an artificial mound thrown up to form the site of an ancient lake-dwelling (a "crannog").

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after'. A little later, Mr H. D. Geldart called further attention to this locality2, which he had visited (as he informs me) in company with Miss Smith and the late Mr Thomas Dix, a good field naturalist, who had lived formerly at Dickle- burgh. In 1897, Miss A. R. Smith was kind enough to send me fresh specimens, which enabled me to satisfy myself that the plant had really been identified correctly-as to which I had, I confess, a lingering doubt3. For yet further information, I was indebted to the kindness of the late Rev. C. E. Peck, of Diss, who had been familiar with the locality for eight or ten years. He it was who guided Dr Moss and myself to it, on 8 April, 1912, when we found the plants (probably less than two score4) growing in association with about as many Cowslips and perhaps a dozen hybrids between the two. The foregoing are all the outlying localities for the Oxlip which exist, so far as I know; but there can hardly be a doubt that careful search of the stretch of Boulder Clay lying to the north and north-east of the eastern Oxlip District would reveal the existence of other outliers, most likely in " carrs" and boggy meadows beside small streams5. In particular, it seems very probable that, in addition to Honington6, various other places in the valley of the (? nameless) stream running north from Tostock which Hind gives7 as localities for the True Oxlip, may really be such, as Hind thought, and are not merely localities for the Common Hybrid Oxlip, as I surmised when I wrote in 18978. This is all the more probable in view of the fact that Hind was rector of Honington, which lies in the centre of the localities in question. They are Fakenham Wood, Sapiston, Troston, Ixworth Thorpe, Barton, Nowton, Walsham, Pakenham, Gt Finborough, and Timworth Wood9. I suggest to local botanists that they should search out these localities and re-examine them with care. As to the question whether localities for the True Oxlip (P. elatior Jacq.) exist in other parts of Britain, I am unable to give any definite reply. The existence of such (either "Areas " or "outliers," in the sense in which I have used these terms) is certainly not impossible. There are, indeed, countless records of the occurrence of the plant in nearly all parts of Britain; but there I See his Flowering Plants, &c., of Harleston, p. 85 (1888). 2 Trans. Norf. and Norw. Nat. Soc. 4 (1889), pp. 579 and 722. 3 See post, p. 207 n. 4 Miss Smith believed they had decreased both in number and in size in recent years; but the Rev. C. E. Peck believed that there had been no decrease during the time he had known the patch. 5 Its occurrence at Exning, near Newmarket, has been reported to me; but Mr A. H. Evans of Cambridge, who has been good enough to search that parish has failed to find it. Again, I have been informed of its occurrence at BotesdaleandRickinghall,in Suffolk; butMrArthur Mayfield has carefully searched those parishes, together with the adjoining parish of Redgrave, and has found no trace of it. 6 See ante, p. 205. 7 Flora of Suffolk, p. 282 (1889). 8 Op. cit. pp. 186-187. ' All these are in Hind's District I, which covers the north-eastern quarter of the county. Stow Langtoft, in the same district, might probably be added; for, in Hind's Herbarium, there is a specimen from there, which, though labelled "P. veris," seems to be the True Oxlip. On the other hand, I doubt whether any single one of Hind's many records of "P. elatior" in other parts of Suffolk relates to the True Oxlip.

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can be no doubt whatever that these refer (almost, if not quite, without exception) to the Hybrid Oxlip (P. veris x vulgaris), which occurs commonly, though always sporadically and nowhere abundantly, throughout Europe, wherever the two parent species grow in close proximity. During many years past, I have investigated, either by correspondence, personal visits, or other means, scores of these records, some of which appeared, at first sight, quite good; but, in every single instance, I have been able to satisfy myself (though absolute proof has generally been unobtainable) that the Hybrid had been mistaken for the True Oxlip1. Still, there may be in Britain other localities for the True Oxlip, as yet overlooked. It has been pointed out already that all the known outlying localities for the Oxlip lie to the north or north-east of the large eastern District: none (so far as is known) to the west, south, or south-east of it. The question naturally arises: Why is this: how does it come about? To this, it is impossible to supply an entirely satisfying answer. I suggest, however, that all the known facts go to show that, in Britain, the Oxlip is a declining species which is undergoing a slow, but steady, contraction of the Area occupied by it. I suggested long since2 that, in this country, it is gradually undergoing extermination through hybridization with the more potent Prim- rose all round the margin of its Area. In any case, the contraction must necessarily have gone on wholly or mainly from the north; for, to the north and north-east of the present Oxlip Area, there lies (as noticed above) a great extent of elevated and largely-unbroken Boulder Clay, the whole of which (one may fairly assume) was once occupied by the Oxlip-an assumption which is supported by the existence within it of the outlying localities described above; while, to the east, south-east, and south, the Boulder Clay extends no more than a few miles and lies everywhere at a very low elevation. Probably, therefore, the Oxlip Area never extended more than a few miles further east or south than it does to-day. On the whole, then, one may say with fair confidence that the Oxlip outliers described above are survivals from a time when the Oxlip's range extended further north than it does now, covering the region in which these outliers are found; also that they are apparently not newly-established colonies (so to speak) and do not indicate a tendency on the part of the plant to extend its Area3.

1 Such are, for instance, Miss Mary Kirby's record for various woods in Leicestershire (Leicest. Flora, p. 114: 1850); Mr J. E. Griffith's record for Great Orme's Head (Fl. of Anglesea and Carnarvonshire, p. 93: 1895); Trimmer's record for Flordon, Norfolk (Fl. of Norf., Suppt., p. 47: 1889); Woodruffe-Peacock's record for Great Ponton, Lincolnshire (Journ. of Bot. 44, pp. 242-243: 1906); and Howard Candler's statement that it is "generally distributed" in woods throughout Rutlandshire (V.C.H., Rutlandshire, 1, p. 31: 1908). My experiences in connection with these investigations have been such as to incline me to speak always of the Hybrid Oxlip as the "Hoaxlip." 2 Op. cit. pp. 195-196. 3 It is not impossible, however, that some of the Oxlip outliers which exist on boggy alluvium beside streams, may owe their origin to seeds carried down by these streams from the higher ground nearer the centre of the Oxlip Area.

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One may regard the Oxlip as probably a species which reached Britain, among other hardy colonists, soon after the end of the last Epoch of Glaciation and occupied here a wide area, covering probably the whole extent of the Chalky Boulder Clay and perhaps other calcareous soils as well. Its once- extensive Area here is, however, now decreasing. That this is not due to climatic causes is clear; for, within the Area which the plant still occupies, it grows everywhere in immense profusion. Moreover, the plant has an extremely wide vertical range, showing that it is hardy and able to wfthstand widely- differing climatic conditions'. The decrease in the extent of the Oxlip Area in Britain is due solely, I believe, to the attacks (so to speak) being made upon it incessantly, all round its margin, byits more-potent nearallythe Primrose, which is, I hold, slowly, but steadily, hybridizing it out of existence in this country2. The Primrose, on the other hand, was probably a comparatively late arrival. It is a virile "pushful" species and is capable of flourishing upon a considerable variety of soils, not being dependent, like the Oxlip, upon one which has both a high lime-content and a high water-content. Consequently, it has a range which extends both further south and further north than that of any other species of the genus-from the north of Africa to the Faroe Islands. In the British Isles, no plant has a wider distribution, and it flourishes exuberantly, even in Shetland3. The foregoing observations seem to suggest a solution of the puzzling fact that the Primrose, though it grows abundantly all round the Oxlip Area, is entirely absent from that Area. One may surmise that, though the aggressive Primrose has completely surrounded and greatly reduced the ancient Oxlip Area, it has not yet succeeded in penetrating to its interior, where the Oxlip remains entrenched (as it were) upon the highest points of its once much more extensive Area, though gradually losing more and more ground, owing to the attacks being made upon it incessantly, all round its margin, by the ever-advancing Primrose.

1 Thus, I have seen it flourishing equally well (though differing much in size) in meadows near Alost, in Belgium, at an elevation of no more than 30 to 40 feet, and in the Alpine pastures of the Ober Engadin, in Switzerland, at an elevation of over 6000 feet. 2 Evidence that the small western District, at least, is becoming gradually more restricted is to be found, apparently, in Madingley Wood, about four miles west from Cambridge, about three miles east from the neare?t point on the margin of the western District, and lying on the Boulder Clay at an elevation of about 150 feet. Ray recorded the Oxlip as growing abundantly in the wood some 260 years ago (Cat. Plant. circa Cantab. nascent, p. 71: 1660). I visited it in 1896, when I could see Primroses only in it; and Mr I. H. Burkill, who had searched it previously, informs me that, as far as he could see, the Oxlip had become extinct. In any case, this western District is so small, and so large a proportion of its area is, in consequence, exposed to the hybridizing influence of the Primrose all round its margin, that one may fear it will, within a comparatively short time, either sink to the status of a mere " outlier " or disappear altogether. Mr Adamson's description of the intermingling of the plants as he saw it in 1912 (see Trans. Bot. Soc. Edinb. 24, p. 85) suggests that this process had advanced perceptibly since I visited the District in 1896. 3Watson says (Topoqr. Bot. p. 334) that "it is doubtless to be found in every county," and More says (Cybele Hib. p. 231: 1898) that it occurs "throughout Ireland."

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There is one other curious point in connection with the outlying localities for the Oxlip to which attention must be drawn: namely, the common occurrence in them of hybrids with the Cowslip (P. elatior x veris). Ordinarily, in Britain, this is a very rare hybrid and occurs in woods only. In the 40 years during which I have been studying our British Primulas (especially the Oxlip), I have certainly not seen as many as 40 plants of it, other than those I have seen in these extremely-small outlying localities. Yet, in them, plants of this rare hybrid are, though few in actual number, extraordinarily numerous in proportion to the number of plants of either of the two parents. Indeed, if my memory serves me right (for I have attempted no actual census of plants), there were present in the outliers at both Cavenham and Dickleburgh almost as many plants of this hybrid as of either of the two parents-a highly remarkable fact in view of the striking rarity of the hybrid elsewhere. Again, the question naturally arises: Why the exceptional profusion of this hybrid in these outliers: how does it come about? Hitherto I have been accustomed to explain its rarity in ordinary circumstances by citing the facts that the two parent species have different habitats (the Oxlip being almost always an inhabitant of woods: the Cowslip, of open meadows) and that the flowering-times of the two species are not quite synchronous (the Oxlip flowers being almost over before those of the Cowslip are fully out). Without doubt, these considerations hold good ordinarily; but, in the case of these outlying localities for the Oxlip (most of which are more or less in the open, often in boggy riverside meadows), the first consideration obviously does not apply (for, in them, both species grow together); while, as regards the second, the flowering-times of the two species are probably, in these circumstances, sufficiently synchronous to permit of hybrids between the two being produced.

POSTSCRIPT.

The Editor has raised a query as to what I mean when I assert my belief that the Primrose is slowly hybridizing the Oxlip out of existence in this country, and has asked exactly how I suppose this result is being brought about. I have long had ideas on this point, but have hesitated to express them, because they are mainly speculative and must, I fear, remain so; for it would be practically impossible (as it seems to me) to prove or disprove them effectively, either by observation or by experiment-at any rate, not without taking, actually in the field, an enormous amount of trouble spread over many years. However, as the point has been raised, I submit that the following is probably something approaching what occurs: Take the case of a wood full of Oxlips on the extreme margin of the Oxlip Area and having, immediately adjacent to it, a meadow with an abundance of Primroses on the banks and in the ditches around it. When the time comes for the wood to be cut, the Oxlips, stimulated bythe sudden access of abundant light

Journ. of Ecology X 14

This content downloaded from 130.63.180.147 on Mon, 27 Jun 2016 10:58:34 UTC All use subject to http://about.jstor.org/terms 210 Primula elatior Jacquin: its Distribution in Britain

and warmth, begin to grow and flower in extreme profusion, as I have described elsewhere. At the same time, the removal of the undergrowth enables bees and other insects to convey pollen from the Primroses outside the wood to the Oxlips within it; for there are species which are known to visit both. The result is that, in the course of a couple of years or so, a large number of very-vigorous hybrids between the two appear. By this time, however, the wood has begun to grow up; whereupon the Oxlips and the hybrids alike become largely dormant; and nothing happens for the next dozen years or so. Then the wood is cut down again; such Oxlips and hybrids as have survived soon come to life once more; the remaining Oxlips are exposed again to the hybridizing visits of insects; and the result is more hybrids. But, all this time, the original Oxlip plants have been steadily dying out; for their natural duration of life is probably no more than a few years, though I do not know exactly what it may be in actual fact. Anyway, by the time the wood has been cut twice or thrice, with the results described above, it seems likely that all the Oxlips growing within reach of the hybridizing action of the bees (which is known to extend to at least a mile) will have died off naturally, leaving no pure descendants, but a number of hybrids, in possession of the ground. But the hybrids also are mortal (so to speak)-possibly even more so than the pure Oxlips; and, in time, they also will have died out. Probably they would do so without leaving any descendants; for, though (like most first-cross hybrids) they are themselves particularly robust and vigorous in growth, they are, nevertheless, extremely sterile1-so much so that I am not conscious of having ever seen a plant which appeared to be a second-cross hybrid. In the course of time, therefore, the ground formerly occupied by Oxlips would become denuded of both them and their hybrids, and would remain unoccupied by any species or form of Primula, were it not reoccupied by either Oxlips from one side or Primroses from the other. But all observation goes to show that (in Britain, at any rate) the Oxlip, for some reason, never advances and never extends its boundary2. On the other hand, there is much to show that the Primrose is an enterprising and ever-advancing species (" aggressive," I have called it) which does, by some means, advance and extend its boundaries. It, therefore, is the species which comes ultimately to occupy the ground from which the Oxlip has been driven-"hybridized out of existence," as I have said.

1 Miss E. R. Saunders has demonstrated this by actual experiment (see a forthcoming paper in The New Phytologist). The great sterility of the hybrid P. veris x vulqaris has been noted by many observers. Kerner asserts (Nat. Hist. of Plants, 2, p. 404) that the same is the case with the hybrid P. elatior x veris. 2 See Journ. Linn. Soc. Bot. 33, p. 195.

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