O* c\* so: OF THE * U N I VERS ITY or ILLINOIS wa-3 BTOlOOV SIOL06I Return this book on or before the Latest Date stamped below. Digitized by the Internet Archive in 2018 with funding from BHL-SIL-FEDLINK * https://archive.org/details/reportofconferen3195bota THE CHANGING FLORA OF BRITAIN f THE CHANGING FLORA OF BRITAIN BEING THE REPORT OF THE CONFERENCE HELD IN 1952 BY THE BOTANICAL SOCIETY OF THE BRITISH ISLES EDITED BY J. E. LOUSLEY 1953 Printed by T. Buncle & Co. Ltd., Market Place, Arbroath, for the BOTANICAL SOCIETY OF THE BRITISH ISLES AND OBTAINABLE FROM THE SOCIETY, c/o DEPARTMENT OF BOTANY. THE UNIVERSITY, OXFORD. rf/ • f 3 CONTENTS Editorial Nbt© ... ... ... ... ... ... ••• Programme of the Conference List of Botanists who attended the Conference ... The Significance of a Changing Flora. Rev. Canon C. E. Raven ... ... ... ... ... ... Natural Factors contributing to a Change in our Flora. Prof. T. G. Tutin Human Factors contributing to a Change in our Flora. Prof. A. R. Clapham ... Page 7 8 11 14 19 26 Possible Human Historical Factors determining the Distri¬ bution of Eriophorum latifolium in the North-west Conway Valley. Dr. R. Elfyn Hughes ... ... 40 ^ Some Recent Modifications in the Flora and the Vegetation of the Valois. Dr. Paul Jovet 1 Recent Additions to the British Flora. R. D. Meikle ... V A Zoologist’s Approach to a Changing Flora. Dr. Maurice ■v Burton British Vegetation in the Full-glacial and the Late-glacial Periods. Dr. H. Godwin . v» \ Some Late-glacial Plants. D. Walker & R. G. West Present-day and Late-glacial Distribution of some Alpine Vascular Plants in Scandinavia and their interpre¬ tation. Dr. Eilif Dahl Glacial Relics in the Netherlands. Dr. Ch. H. Andreas ... Some Parallels between the British and Scandinavian Mountain Floras Dr. A. Melderis ^The North American and Lusitanian Elements in the Flora of the British Isles. Dr. J. Heslop-Harrison ^The Continental Element in our Flora. Dr. S. M. Walters 46 49 52 59 75 77 84 89 105 124 Page A Changing Flora as shown in the Study of Weeds of Arable Land and Waste Places. Sir Edward Salis¬ bury ■ ii> tia a • • . .. . .. ... 130 The Recent Influx of Aliens into the British Flora. J. E. Lousley 140 Wool Aliens in Bedfordshire. Dr. J. G. Dony ... ... 160 Epilobium pedunculare in Britain. Miss A. J. Davey ... 164 Epilobium adenocaulon in Britain. G. M. Ash ... ... 168 A Changing Flora as shown in the Status of our Trees and Shrubs. Dr. E. F. Warburg . 171 Human Influence on Hybridisation in Crataegus. A. D. Bradshaw . 181 Is the Box-tree a Native of England? C. D. Pigott & Dr. S. M. Walters . 184 The Conservation of British Vegetation and Species. Sir Arthur Tansley 188 Concluding Remarks by the President ... ... ... 197 Field Meeting to the Neighbourhood of Ashford, Kent ... 198 I n dox ... ... ... ... ... ... ... ... 200 7 EDITORIAL NOTE The papers read at the third Conference arranged by the Botanical Society of the British Isles proved of such outstanding interest and importance that the Council of the Society decided to make them available to a wider public. The pages of this volume include a very high proportion of information and original thought not available elsewhere. “ The Changing Flora of Britain ” was selected for the title of the Conference as a theme likely to bring together studies of very diverse aspects of the study of British botany. The record in this book will show how successfully this was achieved and how each paper contributed to the general theme. Approaches to the subject include the evidence derived from ecology, palaeobotany, phytogeography, the recent introduction and spread of aliens, and the special study of trees and shrubs. The papers have been arranged for publication in the sequence stated — the order in which they were delivered at the Conference is set out in the Programme printed on the next two pages. The valuable contri¬ butions of botanists from abroad and of a zoologist have been included in appropriate positions in the book. Scientific names used in the papers are those selected by the speakers and it has not been thought advisable to attempt to standardise them. Where authors’ names are omitted the nomen¬ clature is generally that adopted in current British ecological work as given in the Check List of British Vascular Plants (1946: J. Ecol., 33, 308-347) and Clapham, Tutin and Warburg’s Flora of the British Isles, 1952. Distribution maps are printed as sub¬ mitted by the contributors. The arrangements for the Conference were in the hands of the Meetings Committee of the Society and most of the work fell on Dr. J. G. Dony, Honorary Field Secretary, and Mr. W. R. Price, Honorary Assistant Secretary. The success of the Conference was due to their energy and enthusiasm, together with that of the other officers and members who assisted in the organisation. We are indebted to the British Council for grants which made it pos¬ sible to invite Dr. P. Jovet and Dr. Ch. H. Andreas to come to the Conference to read their papers. We are also grateful to all the other people and bodies who assisted. I should like to take this opportunity of acknowledging the assistance of all those who kindly gave permission for repro¬ duction of maps or base maps used in connection with the illustra¬ tions. Thanks are also due to the members of the Publications Committee who read the proofs of this book and to Mr W. R. Price who prepared the index. J. E. Lousley. 8 CONFERENCE PROGRAMME 1952 THE CHANGING FLORA OF BRITAIN FRIDAY, April 4th First Session 10.30 a.m. The Significance of a Changing Flora The President : The Rev. Canon C. E. RAVEN 11.00 The Historic Element in our British Flora: Full- Glacial and Late-Glacial Floras Dr. H. GODWIN 11.50 A Changing Flora as shown in the Study of Weeds of Arable Land and Waste Places Sir EDWARD SALISBURY 12.45 p.m. Interval for Luncheon Second Session 2.15 Exhibit: British Late-Glacial Plants Mr. D. WALKER and Mr. R. WEST 2.30 Natural Factors contributing to a Change in our Flora Prof. T. G. TUTIN 3.10 Glacial Relics in the Netherlands Dr. CH. H. ANDREAS (Groningen). 3.25 The Continental Element in our Flora Dr. S. M. WALTERS 4.15 Interval for Tea Third Session 5.00 Exhibit : Some Post-war Additions to the British Flora Mr. R. D. MEIKLE 5.15 The North American and Lusitanian Elements in our Flora Dr. J. HESLOP-HARRISON 6.00 * Exhibit: Some Parallels between British and Scan¬ dinavian Plants Dr. A. MELDERIS 6.15 Exhibit: Subfossil and Present-day Distributions of some Scandinavian Alpine Plants and their Inter¬ pretation Dr. E. DAHL (Oslo). 9 10.30 a.m. SATURDAY April 5th First Session Human Factors contributing to a Change in our Flora Prof. A. R. CLAPHAM 11.15 Exhibit: Epilobium adenocaulon in Britain Mr. G. M. ASH 11.30 The Zoologist’s Approach to a Changing Flora Dr. MAURICE BURTON 12.15 p.m. Exhibit: Possible Human Historical Factors in the Distribution of Eriophorum latifolium and other Species in the Conway Valley Dr. E. HUGHES 12.30 Interval for Luncheon 2.00 Second Session A Changing Flora as shown in the Status of our Trees and Shrubs Dr. E. F. WARBURG 2.55 The Recent Influx of Aliens into the British Flora Mr. J. E. LOUSLEY 3.45 Exhibit : Wool Aliens Dr. J. G. DONY and Mr. J. E. LOUSLEY 4.00 Interval for Tea 4.45 Third Session Exhibit : Is the Box Tree a Native of England ? Mr C. D. PIGOTT and Dr. S. M. WALTERS 5.00 Exhibit: The Changing Botanists of Britain Mr. D. E. ALLEN 5.15 The Conservation of British Vegetation and Species Sir ARTHUR TANSLEY 6.00 Closing Remarks by the President 10 "V • SUNDAY, April 6th FIELD MEETING TO THE NEIGHBOURHOOD OF ASH¬ FORD (KENT) TO STUDY THE STATUS OF THLASPI ALLIACEUM (The programme printed above is as circulated before the Conference. It was carried out as stated. One additional paper was read during the Third Session of Friday, April 4th: — Some Recent Modifications in the Flora and the Vegetation of the Valois. Dr. P. JOVET Two additional exhibits were included in the Second Session of Saturday, April 5th: — Exhibit: Man’s Influence on Hybridisation in Crataegus A. D. BRADSHAW Exhibit: Epilobhim pedunculare A. Cunn. in Britain Miss A. J. DAVEY) 11 LIST OF MEMBERS AND GUESTS WHO ATTENDED THE CONFERENCE, April 4 and 5, 1952 (The following list includes only those who attended the meetings held at the Royal Horticultural Society’s New Hall, Greycoat Street, Westminster, London, S.W.l. It is known to be incomplete and we have been unable to give the names of some of the guests in full). G Miss D. M. Allen Miss W. J. Cornwell G K. L. Alvin G Miss E. Coster G J. S. Anderson Miss F. E. Crackles G Dr. C. H. Andreas G Miss R. Crowe G. M. Ash G Dr. E. Dahl Miss D. E. Ashhurst G D. K. Dalby G Associated Press G Miss A. J. Davey G — Austin Miss E. W. Davies G Miss A. Baigent Mrs H. R. Davies Dr. H. G. Baker G R. K. Davies Miss 0. Balme G R. V. Davies E. B. Bangerter Mrs. M. L. Davis G R. Barrett Miss A. M. Davison G Miss M. Baulch G Miss J. Dawson Miss D. Baylis G Miss J. Dilnot Miss D. Bexon Dr. J. G. Dony G Miss S. Billowes G B. M. Doouss Miss N. M. Blaikley G B. Douglas G Miss P. A. Body G B. D. Dowker R. A. Boniface R. B. Drummond M. Borrill G B. F. T. Ducker G J. M. Boutwood G T. R. Eagles A. D. Bradshaw Rev. E. A. Elliot J. P. M. Brenan Dr. A. G. Erith D. Brett G Miss E. M. Evans Miss W. M. A. Brooke G C. Farmer G Miss Brown Mrs. P. R. Farquharson G. M. Brown G J. Farrand G J. M. B. Brown G Miss S. Feinsilber 0. Buckle R. S. R. Fitter G Miss Burbidge G Miss M. Fox Dr. R. C. L. Burges Miss L. W. Frost G Dr. M. Burton Miss H. D. Garside Dr. R. W. Butcher P. Gay G Miss Bywater Miss E. J. Gibbons J. F. M. Cannon Mrs. A. N. Gibby G Mrs. B. K. Chadwick G D. R. Glendinnlng G N. L. Chadwick K. M. Good way G P. A. Chalk W. B. Gourlay G Miss K. M. Chalklin R. A. Graham G Miss M. Charlton P. S. Green J. Chidell P. Greenfield Prof. A. R. Clapham G Miss R. M. Greenhow Dr. W. A. Clark H. C. Grigg G M. J. Cole J. D. Grose G R. G. Coleman Miss C. Gurney G Miss B. Coles G — Hadley G C. P. Colles Mrs. E. M. Haines T. G. Collett G Dr. G. Haskell G — Collins Mrs. B. F. Hassall G R. Comber G Miss M. J. Hawkins Miss A. Conolly F. N. Hepper D. E. Coombe Miss M. J. Herbert 12 G Miss E. A. Herridge Dr. J. Heslop-Harrison G Mrs Heslop-Harrison Miss O. Holbek B. Hopkins G J. Hughes Dr. M. G. Hughes Dr. R. E. Hughes G Miss M. J. Humphreys G Miss Humphrys G H M. Hurst H. A. Hyde Miss M. Isaac Miss E. Isherwood G B. Ivimy-Cook G W. Jackson G Miss F. Jarrett G Dr. P. Jovet G Mme. Jovet D. W. Jowett D. II. Kent G Miss M. L. Kenyon Dr. J. M. Lambert G Miss J. M. Laptain G G. F. Lawrence G Miss P. Lewis G — Limbird Miss S. M. Littleboy Miss C. Longfield J. E. Lousley J. D. Lovis Dr. A. G. Lyon D. McClintock G Miss C. C. D. MacDonald J. MacDonald Prof. R. C. McLean Dr. K. N. G. MacLeay G Miss V. A. Martinson R. D. Meikle Dr. A. Melderis G Dr. Melouk Dr. R. Melville Dr. B. MerTiman D. F. S. Miles E Milne-Redhead J. Moor Miss B. M. C. Morgan G G. H. Morgan Miss C. W. Muirhead G — Nathani E. Nelmes Miss S. Nelmes G Miss J. E. Nettleton-Hill P. J. Newbould P. M. Newey G A. H. Norkett P. R. Norman G D. Oldroyd G Prof. T. G. B. Osborn P. H. Oswald J. Ounsted G J. G. Packer Miss P. A. Padmore G R. E. Parker G Miss S. Parkinson G M. J. Parr G Miss A. K. Patrick G D. J. Payne G H. W. Payton G — Pearson G Miss M. Philips C. D. Pigott G Miss J. Pistel G Miss F. A. Pomeroy M. E. D. Poore D. L. H. Porter G B. Potter G G. Pozniak W. R. Price Dr. C. T. Prime G N. M. Pritchard G Miss J. P. Pugh Rev. Canon C. E. Raven R. C. Readett G Dr. W. Rees Prof. P. W. Richards Miss C. M. Rob G C. F. Roberts G Miss M. Roberts N. K. B. Robson G Miss N. W. Rofe F. Rose Miss E. M. Rosser G Royal Society (Secretary) Mrs. B. H. S. Russell G J. S. Ryland G Sir Edward Salisbury R. E. Sandell N. Y. Sandwith G Mrs. K. N. Sanecki G J. Sansome G J. A. Sargent G J. R. K. Savige Miss M. Scholey G S. Seagrief H. K. Airy Shaw G — Shibko N. Douglas Simpson G — Skellam G Miss J. Skinner Dr. W. J. L. Sladen Mrs. L. M. P. Small G J. Smart G Miss P. M. Smith Dr. E. Smithson Mrs M. Southwell J. S. L. Stephens G D. A. Sturdy Y. S. Summerhayes Miss A. K. Swaine G G. L. Swales E. L. Swann Miss A. C. Tallantire Sir Arthur Tansley 13 Miss Taylor G P. Taylor G J. A. Thelwall G Dr. A. S. Thomas G M. P. Topping Prof. T. G. Tutin J. G. Vaughan C. G Miss M. Viewing G A. E. Wade D. Walker G T. G. Walker E. C. Wallace Dr. S. M. Walters Dr. E. F. Warburg Mrs. Warburg B. T. Ward Dr. A. S. Watt Mrs. W. Boyd Watt Dr. E. V. Watson G P. Watson Dr D. A. Webb Mrs. B. Welch J. D. Weller Dr. C. West R. West A. W. Westrup Miss D. M. Wethered Miss C. A. Whallcy A. W. Wheeler Dr. J. B. White Miss M. M. Whiting Miss M. Wickson Wild Flower Society (Secretary of) Miss J. E. Wilkinson I. A. Williams Miss B. Wilson Miss A. F. Wood S. R. J. Woodell J. F. Woolman Mrs. D. A. Wright P. F. Yeo Dr D P Young 14 THE CHANGING FLORA OF BRITAIN THE SIGNIFICANCE OF A CHANGING FLORA The Rev. Canon C. E. Raven. The President of the Society in opening the proceedings of the Con¬ ference read the following paper : — It is a terrifying honour, for one whose claims to the title of botanist are of the slenderest, to be asked to introduce a Confer¬ ence on so large and fascinating a theme and of so distinguished and expert a personnel. Nor does the work that I have been able to do on the early students of the British flora give me as much material as might be expected. For, as you all know, the Cata¬ logues compiled by the greatest of them, John Ray, and even the less reliable lists by Thomas Johnson or the Herbals of William Turner, John Gerard and John Parkinson, testify rather to persistence than to changes. Apart from the loss of the two fen Senecios and one or two other residents, the plants which Ray recorded so meticulously can still be found, like Eryngium cam - pestre or Veronica spicata, in the same precise localities as in his day. Some of his aliens have been lost and of the very many more that have since been added it is by no means usual for them to establish themselves permanently; species like Epilobium angustifolium, or Senecio squalidus or Juncus tenuis are a rela¬ tively small number. Some years ago I sent to Mr. A. J. Wilmott a list of additions and corrections to Clarke’s First Records, and am probably not alone in hoping that a fully revised edition of that valuable work will soon be undertaken. But, all things considered, the number of emendations is not large. Before leaving early records I may perhaps report one that surprised me. Bound up with the original manuscript of Mouffet’s Theatrum Insect ovum y now in the British Museum, is a holograph letter to Thomas Penny, Mouffet’s friend and the principal author of the volume, from his friend, the Somersetshire doctor William Brewer, In this, along with information about insects, is a detailed and exact account of a weed, which had appeared in his garden and which from the description of its seed-vessel and seed-dispersion and from its name, is beyond any doubt Oxalis corniculata. It was interesting to discover that this denizen, which is commonly regarded as a recent arrival, was a garden weed in the west country nearly four centuries ago — in or about 1585. Obviously, with the colossal changes that have taken place in speed and range of transport, the invasion of Britain by aliens of every kind has been enormously increased. Problems like the assortment of mid-European species in the bomb-crater at Box Hill, or the arrival and hybridising of Australian Junci in the THE SIGNIFICANCE OF A CHANGING FLORA 15 gravel-pits at Eaton Socon, or the strange appearances of the New Zealand Epilobium pedunculare in Northern Ireland, on Plynlimmon and in Ross-shire almost simultaneously, seem to defy explanation. Those like the American denizens of lease- lend carrot fields at the close of the war, or the Australasian con¬ comitants of shoddy, or the mixed intruders which make the sidings at Burton such a happy hunting-ground, are more likely to yield permanent additions. But I confess that such obviously human-borne seedlings do not seem to me to deserve much con¬ sideration. I am not convinced that we ought not to advocate definite action to prevent their settlement — instead of which, alas, I waste my time in painting their pictures. There ought at least to be a clearer policy in determining their claim to inclusion in our flora. Among these casual introductions is one — Spartina cdtemiflora — which though of little scientific importance in itself seems very significant in its offspring. The original species has apparently almost died out — why, in view of its vitality on the mud-flats in Massachusetts Bay, is difficult to explain. But in producing Spartina Townsendii it has raised an issue not only for the geographer but for the theoretical biologist. Of its immense vigour those of you who know how seriously its appearance off the mouth of the Manchester ship-canal endangered our national safety in the war will be fully aware. It is obvious that like other famous hybrids, Poa annua and Galeopsis Tetrahit for example, it has a vitality and invasiveness out of all proportion greater than its parents. One is obliged to ask what part such hybrids have taken in the whole course of evolution? What is the cause of their amazing efficiency? and how far do they supply an analogy for similar developments in zoology? I have long suspected that fertile hybrids between distinct species might be a not unimportant factor in the process of creation, but the only zoological example that I have investigated — the moth now called Arenostola brevilinea — if a hybrid is one whose metamor¬ phosis makes it very ill-suited for laboratory study. Botanical geneticists should have a better chance of investigating such pro¬ blems. At risk of seeming to go beyond the scope of our programme — I must add that, while the changes in our flora by invasion give rise to a number of fascinating ecological, physiological and chemical problems which deserve full investigation, for my own part I must draw attention to changes which raise rather different issues. Here is the point to which I specially desire to draw attention — the changes taking place in our flora not by introduction from outside, nor by changes in the status and distribution of native species, but by the extreme variability of many of our most familiar groups. In Britain we have a relatively small area, widely varied in soil, altitude, character and climate, closely 16 THE CHANGING FLORA OE BRITAIN studied over a long period, and the home of a remarkable number of still varying aggregates. I need hardly remind you of the great apomictic groups — Hieracium, Taraxacum, Rubus, Rosa, Alchemilla, and of the (usually) normally sexed groups Ranun¬ culus aquatilis agg., Viola, Euphrasia, Polygonum, Salix, Orchis, Carex flava agg., Bromus secalinus agg., Festuca and Poa. But it is worth drawing attention to the fascinating problems which these present not only to the systematist but to the biologist, and to the need for far wider and deeper study of them than has yet been made. We all know how elaborate has been the work of students like Ley and Marshall and Pugsley on the Hieracia , or of Riddels- dell, Watson and a host of others on the Rubi; we know, too, of the hundreds of named forms in both genera and of the enormous difficulties of identification and nomenclature that have resulted. For “our changing flora” it is pretty evident that new varieties are still being discovered and indeed are almost certainly coming into existence. (I cannot speak with knowledge of Rubus: but my son’s work clearly indicates this in Hieracium). I should be the last to decry the value of this intensive study or of the interest of the questions that arise from it : those who dismiss apomictic variants as infinite and meaning¬ less can hardly have given the subject much attention. But nevertheless it remains true that quite insufficient work has been done in demonstrating what are the characteristics that are genetically significant, and it is not easy to show which of the differentia employed (for example in Pugsley’s great monograph) represent a real variation and which are merely due to local and environmental influences. The fact is that almost no cytological and physiological study of the genus has been carried out in this country, and that even the cultivation of the varieties has been casual and directed chiefly towards the noting of its superficial effects. Nor does the treatment of the genus by biologists reveal much except guess-work and speculation. When for example Professor Stebbins in his joint monograph on the American members of the genus Crepis deals with its apomictic species he is content to describe the general problem of apomixis, to dismiss the details of the variation as unimportant and to claim that the loss of sexual propagation and the consequent greatly increased varia¬ bility indicates the last struggle of a type which like his one example, Houttuynia cor data, is on its way to extinction. When in his large and more recent volume, Variation and Evolution in Plants, pp. 396-419, he sums up the subject, he supports this verdict by a piece of remarkable special-pleading. For he claims that whereas sexually reproduced forms have both a wider range of gene-combination and the possibility of mutations, apomicts are dependent only upon the combinations in the original parents from which they as hybrids are derived. He omits altogether the two facts (1) that even if apomicts have theoretically a smaller THE SIGNIFICANCE OF A CHANGING FLORA 17 range of combination yet in fact they do display a much larger incidence of variation and in consequence a much greater power of adaptability, and (2) that apomicts, as C. H. Ostenfeld has demonstrated, are as liable to mutation as any other plants. Moreover, though there may be in Houttuynia an example of a dying type, it is ridiculous to speak of Hieracium or Rubus in such a category. It would, in fact, be much easier to argue that, although no doubt the stabilising influence of sex-reproduction may generally be of value to a species, there is plain evidence that, in an environment like Britain where soil, climate, altitude and other conditions vary so widely, a plant that has developed apomictic reproduction and the consequent increased power to perpetuate variations has gained more than it has lost. Obviously the question whether biologically apomixis is to the advantage or disadvantage of the species is one on which presup¬ positions about the worth of sexual reproduction are wholly in¬ sufficient. Professor Stebbins’ guess is as good as any other, but not any better. And the analogies from Drosophila which have overshadowed and dominated Genetics too long are in this case at least meaningless. Obviously, too, we who have so large a number of highly vari¬ able species are in a strong position. Instead of following con¬ tentedly the conclusions of Scandinavian, Danish and German research we should ourselves mobilise a team which could tackle the problems, genetical, cytological, physiological, ecological and chemical, and see whether out of the available mass of material we can not only reach a settled nomenclature and taxonomy (this is relatively unimportant — little more indeed than bare collect¬ ing) but make a serious contribution to the general problems of evolution. It is, to any botanist who comes over to botany from zoology, a sad thing to see how relatively poor has been the con¬ tribution of botanists to the more general study of science and to the answering of the questions on which they ought to have something important to say. May I close these precarious and perhaps impertinent remarks by a personal confession? As primarily an ornithologist I have spent many years pleading that the business of adding new and casual visitors to the Fair Island list or of splitting the Tits into insignificant subspecies was a relatively childish and scientifically valueless pursuit — as compared at least with the study of be¬ haviour. I cannot but make a similar plea to a Conference like this. By all means let us collect and identify and classify our flora, and note additions to it, and calculate their chances of sur¬ vival. But let us remember that this is only preliminary investi¬ gation : we do not learn from it anything of scientific value, un¬ less we use our experience to throw light upon the problems of the relationship of the plant to its environment, of its adaptation and survival, and of the parts played by nature and nurture in its constitution. b 18 THE CHANGING' FLORA OF BRITAIN And here for us in this Society there is a special point to hold in mind. Botany, as I was told recently by a professional botanist who is a colleague and friend to many of us, has always been an amateur’s field of study. “This,” he said, “has its drawbacks if it means that the professional is left to do the strictly scientific work in isolation.” We do not, I fear, make full or wise use of the help that only the man whose whole life is spent on plant-problems can give us. I hope that this Conference, bringing together so large and varied a group of botanists, may do something to bridge the gap that is always liable to open between the field-worker and the expert, the amateur and the professional. NATURAL FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 19 NATURAL FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA T. G. Tutin. I find this a difficult subject to discuss because of the impos¬ sibility of drawing a reasonable distinction between ‘natural’ and ‘artificial’ factors. It is rather like asking “When is an introduced plant not an introduced plant?” There are various unsatisfac¬ tory answers to that question such as “When it was not intro¬ duced by man”, or “When it has been here as long as anyone knows”. Now that it is realised that our records go back for less than a tenth of post-glacial time and that man and other animals have been carrying plants backwards and forwards at least since the end of the Ice Age, it is obvious that these distinctions are neither real nor natural. One may perhaps attempt to distinguish between deliberate introductions by man and unintentional intro¬ ductions. On this basis one may say that natural factors contributing to a change in our flora are all those other than the deliberate actions of man. Whatever one’s views about ‘natural’ and ‘artificial’ or ‘native’ and ‘introduced’, it is clear that two kinds of change can be distinguished : qualitative change and quantitative change. Since the factors involved are largely different these must be considered separately. The three main causes of qualitative change in any flora are evolution, climatic changes and the introduction or extinction of species. The processes of evolution produce the most funda¬ mental, though probably the slowest, changes and since a good deal is now known about them I will spend a short time giving you a few examples of what is going on in our flora at present. There seem to be three main processes at work. The first of these is the gradual differentiation of species through mutation and selection without change of chromosome number, producing in time what Valentine has called g-ecospecies. Then there is the well-known process of doubling, quadrupling and so on, of chromosomes, which appears often to occur in hybrids between species and probably sometimes within species. This produces polyploid series and gives rise to a-ecospecies in Valentine’s con¬ venient terminology. Finally, there is the less well-known and apparently rarer process of aneuploidy which entails the gain or loss of one or a few pairs of chromosomes and also gives rise to a-ecospecies. A comparatively late stage in the first process is to be seen in the primrose ( Primula vulgaris Huds.), oxlip (P. elatior (L.) Hill) and cowslip ( P . veris L.), and a somewhat earlier stage in 20 THE CHANGING FLORA OF BRITAIN the red and white campions (Melandrium rubrum (Weig.) Garcke and M. album (Mill.) Garcke). What appear to be still earlier stages in differentiation which, if my guess is right, is taking place before our eyes in this country, are shown by Veronica spicata L. and Helianthemum canum (L.) Baumg. The former is on the Continent a variable species showing a distinct preference for a continental climate. In this country, on the other hand, there are two distinct populations differing somewhat morphologically and occupying quite separate areas. Subspecies spicata is a small plant of dry chalky heaths in East Anglia where rainfall is low and the annual range of temperature great: subspecies hybrid a (L.) E. F. Warb. is a larger plant with a strongly oceanic distri¬ bution in W. England and Wales where the rainfall is high and the annual range of temperature small. There seems no reason why the isolation of these two should break down and every reason to suppose that as long as it does not, differentiation will continue. There does not appear to be any published information about whether these subspecies are completely interfertile, though recent experiments by Dr. Walters indicate that this is so. Helianthemum canum is another somewhat similar case, though here the Continental as well as the British distribution is markedly discontinuous and, as far as my observations go, each population differs somewhat from the others. Plants from Tees- dale, and Scout Scar near Kendal, may be taken as typical of the kinds of differences which occur and are maintained in cultivation. In the former, the oblong leaves are nearly glabrous on top and reach a length of 10 mm. The stems and sepals have little anthocyanin and the petals are pale yellow, about 5 mm. long and strongly reflexed. The longest branches under garden con¬ ditions grow about 23 cm. a year and the flowers regularly open 7-10 days before those of the Kendal plant when the two are grown side by side. The Kendal plant is densely grey- 1 omen to se and the ovate leaves reach a length of 7 mm. The stems and sepals have abun¬ dant anthocyanin and the petals are deep yellow, about 7 mm. long, and spread horizontally. The longest branches grow about 8 cm. a year, but the majority of them die back in autumn. Both populations have the same chromosome number (n= 11) and appear normally to be selfed and to breed true for the char¬ acters mentioned. Populations of this kind are presumably derived from a formerly widespread and variable species; they seem to me to indicate clearly one method of the production of very local endemics, such as are commonly found in unglaciated regions where there has been far more time for speciation to occur than in N. Europe. NATURAL FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 21 Evolution through polyploidy, when it occurs, is a more striking process because of its abruptness. One of the best known recent examples in this country is, of course, Spartina Townsendii H. & J. Groves, which arose in Southampton Water in the latter half of last century. S. alt emi flora Lois., an American species, became established there, hybridised with our native S. maritima (Curt.) Femald, and the hybrid, through chromosome doubling, gave rise to S. Townsendii, a vigorous plant which is far more successful than either of its parents. This example illustrates the great importance for this method of evolution of any factor (e.g. climatic change or human interference) which brings together allied but geographically isolated species. This has undoubtedly been one of the major factors involved, and it is probably true to say that a-ecospecies are produced most commonly in periods of drastic change while g-ecospecies develop in ages of compara¬ tive stability. Apomixis, and particularly the type known as agamospermy or the production of seeds without fertilisation, is a common, though rather minor, factor involved in the development of new species in some genera in our flora. This process enables hybrids, notably triploids and pentaploids, which would otherwise be sterile, to reproduce successfully, and also produces populations which differ constantly but only to a small extent from others. It largely accounts for the great number of “small” species in genera such as Hieracium and Rubus. It also occurs, though to a lesser extent, in a great number of other genera, for example Ranunculus, Potentilla, Sorbus, and Poa. In certain genera, particularly Carex, aneuploidv is far com¬ moner than polyploidy. Miss E. W. Davies has shown, for instance, that it has probably played a large part in the isolation of Carex flava L., C. lepidocarpa Tausch and C. demissa Homem. from one another. The same process appears to be going on in C. caryophyllea Latour. where Miss Davies has found n = 33 and 34, while Tischler records n = 31 from continental plants. These numbers are associated with considerable size differences and other smaller morphological differences. Turning now to the question of climatic changes, it is impor¬ tant to bear in mind how profound these have been even during the last 12,000 years and what a great effect they have had on the composition of our flora. Dr. Godwin has made this point clear (see pp. 59-74). There is no reason to suppose these changes have ceased, and we would expect some of their effects to be visible. Seven species are stated to have become extinct in this country in recent times and I propose to examine for a moment the case of two representatives from this list, Senecio paludosus L. and Trichophorum alpinum (L.) Pers. These show some similarities in that they are both commonly stated to have been lost through drainage and they both grow in damp base-rich habitats. 22 THE CHANGING FLORA OF BRITAIN Senecio paludosus formerly occurred in fen ditches in four eastern counties. Its distribution on the Continent is fairly wide, extending north to S.E. Sweden, the Baltic States and N. Russia. It is extinct in Denmark and is quite absent from Norway, the west of France and the whole of Portugal; it clearly has a some¬ what ‘Continental’ type of distribution. Fen ditches still exist in abundance, and in S. Sweden the plant can be seen growing in ditches at the margins of fen woods, a type of habitat which is not uncommon in this country. It seems clear to me that it occurred in East Anglia as a relic of a period when our climate was more continental, and that its diminution and ultimate ex¬ tinction was due primarily to climatic change, though the final blow may have been the destruction of one particular habitat or even the excessive attention of some 19th Century botanists. Trichophorum alpinum is predominantly a northern species of lowland habitats which thins out in the south of its range (France, Switzerland, etc.) where it seeks refuge in the mountains and, according to Hegi, reaches altitudes of 2,000 m. It is not so continental in its distribution as Senecio paludosus, but in Scandinavia increases in abundance towards the east, and is entirely absent from Iceland. This continental tendency is more marked in the southern part of its range. It formerly occurred in Angus, which has a less oceanic climate than most of Scotland. Its extinction and its absence from other apparently suitable areas such as the damp, peaty, base-rich habitats which are not in¬ frequent in the neighbourhood of Ben Lawers all suggest that it is another victim of a changing climate. It seems impossible to get any satisfactory evidence about new arrivals, partly because chance plays so large a part and partly because it is never possible to say that a certain species has often before arrived in the country but has been unable to establish itself until the present. Sir Edward Salisbury and Mr. Lousley are dealing with the influx of alien species into this country in detail, but a word or two must be said about it here as at least some plants arrive by what are known as natural means. It seems likely that Alisma gramineum C. C. Gmel. found its way to its one known station near Droitwich on the feet of migrating water-fowl. The fact that it grows in an artificial pond may well be due to the probably less intense competition in such a pond, which would make the initial establishment of the seedlings easier. It has survived in this place for more than thirty years and it is probably only a matter of time before it spreads to other suitable habitats. Scutellaria hastifolia L. is another example of recent introduc¬ tion by unknown but probably ‘natural’ agency. This also has every appearance of being a successful species in this country, as it is known to have spread considerably since its original discovery. In a garden it is all too successful and not only spreads vegeta- tively with great rapidity but produces an abundance of seed. NATURAL FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 23 There are, of course, many examples of unsuccessful introduc¬ tions, among which Inula Britannica L. may be mentioned. This is believed to have arrived in the same way as Alisma gramineum and, like the latter, became established in a man-made habitat, the margin of Cropston Reservoir near Leicester, where competi¬ tion is not severe. It survived for about forty years but has now disappeared completely. It seems undoubtedly to have been some climatic factor which finally killed it, as the habitat has suffered no obvious change and there is no evidence of over-collecting. It may well have been that the summer temperatures were too low to allow adequate seed production and that the original plants reached the end of their normal life. On this point, as on so many other similar ones, there appears to be a complete lack of evidence. It is perhaps worth pointing out that the extinction or increase in abundance of rare plants may be determined by some exception¬ al fluctuation in climate, while the effective establishment of a new migrant probably requires a more lasting though less striking change. It is well known to gardeners, especially after the winter of 1947, that a plant may thrive for a hundred years and then be completely destroyed by exceptionally low temperatures. It would appear to be largely the extremes and not the means of the climatic factors which are of significance in this respect. Quantitative changes in our flora are always going on, though, of course, at varying rates ; in trees they are slowest and in annuals most rapid. They are seldom noticed except among rare plants, or plants that were formerly rare. Such changes are due to two main causes : changing climate or, in annuals, fluctuations in weather from year to year; and drastic changes in habitats, due directly or indirectly to man. The latter, though really outside the scope of this contribution, cannot altogether be separated from the former. One of the most accurately recorded changes of this kind is the spread of Himantoglossum hircinum (L.) Sprengel, which has been described by Good. It confirms the statement made by meteor¬ ologists that there has been a slight but definite improvement in climate since about 1900. The decrease of Scheuchzeria palustris L. is probably primarily due to the same shift in climate, though it is complicated by the drainage of some of the bogs in which the plant formerly occurred. It is, all the same, clear that Scheuch¬ zeria was, and still is, at its extreme south-western limit in this country. To take one former locality as an example, there are still, in spite of drainage, apparently suitable habitats for it in Shropshire. It may also be worth pointing out that some of the New Forest bogs with their abundant Carex limosa L. seem to meet its edaphic requirements, while it is known from Somerset as abundant remains in the peat of the Levels. Man has blamed himself too much and climatic changes not enough for the decrease or extinction of rare species. Cyperus fuscus L. is a good example of an annual which fluctuates greatly in abundance with variations in weather from 24 THE CHANGING FLORA OF BRITAIN year to year. In cultivation it is found to need a relatively high temperature for germination and sets little or no seed at Leicester in a cool summer. Man has undoubtedlv caused its extinction in Middlesex, but there is otherwise no evidence for any permanent change in abundance. Ranunculus ophioglossifolius Vill. shows similar fluctuations both in Gloucestershire and in its northernmost station on the island of Gotland in the Baltic. In both places, however, the amount of bare mud provided by the trampling of cattle seems to be an even more important factor than the weather. In cultiva¬ tion at Leicester, seed was produced abundantly even in the cool summer of 1951. Finally the dramatic spread of certain species in the last hundred years must be mentioned. Two good examples of this are Chamaenerion angustifolium (L.) Scop, and Crepis taraxaci- folia Thuill. The first of these occurs as two so-called varieties, var. macrocarpum Syme and var. brachycarpum Syme. Sower - by’s English Botany says of the former: “in borders of woods, damp places and on rocks. Sparingly, but generally distributed from Somerset and Hants, to Orkney.” Of the latter it says “ in damp woods and by river-sides. Much rarer than var. a, and probably either planted or escaped from cultivation. It occurs in several places in Shropshire; in N. Wales; Hampshire; by the banks of the Swale, Bichmond, Yorkshire; Colinton Woods, near Edinburgh .... it is very commonly cultivated under the name of French -Willow or Bose-Bay.” In Lapland, var. macrocarpum is a common plant while var. brachycarpum is found only beside the railway and in similar dis¬ turbed places. It seems clear that the present great abundance of the plant in this country is due to two factors : first, the intro¬ duction of a new ecotype or subspecies and, secondly, the great increase in suitable habitats due to felling, bombing and other similar factors. It is interesting to note that var. macrocarpum does not appear to have spread from its original habitats and that var. brachycarpum is no longer cultivated in the south, but is sternly discouraged by gardeners, though it may be seen in gar¬ dens and on sale in markets in the Highlands. Crepis taraxacifolia shows a somewhat similar state of affairs though, since it was first recorded as late as 1713, some doubt has been expressed about its status as a native plant. However, as it occurs throughout west Europe, from Spain and Portugal to N.W. Germany, it is possibly indigenous. Turning once more to English Botany we find its habitat and distribution given as “ In chalky places and by roadsides, and in waste places in limestone districts. Local. Plentiful in Kent. It occurs also at Bookham in Surrey ; in Suffolk ; in the south of Essex ; at Scarborough ; and in Caernarvonshire”. This distribution may indicate that it had recently crossed the Channel or that it was successful only in the area of high summer temperatures. Scarborough and Caernar¬ vonshire may have been adventive localities. In any case its NATURAL FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 25 distribution seems to have been much the same in 1884 (J. D. Hooker. Student’s Flora of the British Islands). Since then it has increased in abundance greatly, either owing to climatic change, or the introduction of new ecotypes, though there is no evidence for the latter. It is now one of the two most abundant species of Crepis in England and Wales northwards to Yorkshire and Lanca¬ shire. In conclusion, I would suggest that the two most important natural factors producing changes in our flora are evolution and altering climate, both very powerful and far-reaching, but both slow-acting. There is a great need for more observations about the effects of these factors, and many of these observations can be made by amateurs. The kind of thing that is needed is in¬ formation about flowering, seed production, germination and sur¬ vival, if possible correlated with real meteorological information, not temperatures in a Stevenson Screen, which has never been a plant habitat. This can provide the essential basis for experi¬ ments, which are perhaps best left to the professional who has usually more means, and sometimes more time, at his disposal. REFERENCES. Baker, H. G., 1948, Stages in invasion and replacement demonstrated by species of Melandrium, J. Ecol., 36, 96-119. Clapham, A. R., Tutin, T. G., & Warburg, E. F., 1952, Flora of the British Tales. Cambridge. Coste, H., 1937, Flore de la France. Paris. Coutinho, A. X. P., 1939. Flora de Portugal. Lisbon. Good, R., 1936, On the distribution of the Lizard Orchis (Himantoglossum hir- cinum Koch), New Phytol. 35, 142-170. Hegi, G., 1906-29, Illustrierte Flora von Mittel-Europa. Munich. Hooker, j. D., 1884, The Student’s Flora of the British Islands. London. Hulten, E., 1950, Atlas of the distribution of vascular plants in N. W. Europe. Stockholm. T.id, J., 1944, Norsk Flora. Oslo. Lindman, C. a. M., 1926, Svensk Fanerogamflora. Stockholm. LOve, a., 1945, Islenzkar Jurtir. Lund. SOWERBY, J. E., et al., 1863-72, English Botany. London. Tischler, G., 1950, Die Chromosomenzahlen der Gefdsspfanzen Mitteleuropas. The Hague. Valentine, D. H., 1947, Studies in British Primulas, I, Hybridization between Primrose and Oxlip (Primula vulgaris Huds. and P. elatior Schreb.), New Phytol. 46 , 230-253. - , 1948, Studies in British Primulas, II, Ecology and taxonomy of Primrose and Oxlip (Primula vulgaris Huds. and P. elatior Schreb ), New Phytol. 47, 111-130. 26 THE CHANGING FLORA OF BRITAIN HUMAN FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA: THE FORMER ECOLOGICAL STATUS OF CERTAIN HEDGEROW SPECIES A. R. Clapham. Some years ago Mr. Charles Elton asked me where, in this country or elsewhere, Lamium album was a constituent of un¬ doubtedly natural vegetation, and I found that I could not answer his question. Similar problems about other hedgerow and wayside species had already occurred to me and I began to consider the matter more seriously. This paper embodies reflections on five such species. Since hedges are man-made habitats, and since there is a threat that they may soon become much changed floristically, I claim that my topic lies well within the subject of this conference. Druce, in his Comital Flora (1932), gives the following notes on the species considered in this paper: 1. Aegopodivm Podagraria L. Viatical. British. Alien. Europe. Waysides, hedges, waste ground. P. A persistent garden pest; chiefly near habitations. Lowland, up to 1300 ft. in Yorks. Throughout the British Isles. 2. Chaerophyllum temulentum L.* Septal. British. Hedgebanks, fields, waste places. P. Low¬ land, ascending to 1200 ft. in Yorks. All save 96, 97, 102-104, 107, 108, 110-112. 3. Anthriscus sylvestris (L.) Bernh. Septal. British. Roadsides, hedge-borders, fields under shade of trees. P. Lowland, up to 1200 ft. in Derby; 1750 ft. in Atholl ; 2500 ft. on Brandon cliffs. Throughout Britain save Jersey and Guernsey. 4. Tanacetum vulgare L. Viatical. British. Banks, hedges, waste places. Common. P. Lowland, to 1200 ft. in Scotland. Throughout Britain save 51 ?, 69. 5. Tussilago Farfara L. Agrestal, etc. British. Clayey soils. P. Lowland, ascends from near sea-level to 1950 ft. on Highfield ; 2550 ft. on Snowdon; 3500 ft. on Ben Lawers; 1900 ft. in Co. Down. Abundant throughout the British Isles. All, it will be seen, are species widely distributed in the British Isles but more or less confined to secondary, man-made habitats, so that it is not clear what was their ecological status before *This is as given in Comital Flora. (See also Sprague, Proc. Cotteswold Nat. Fid. Club for 19/.8, 30, 28 (1950)). The spelling used in this paper is C. temulurn L.— ED. HITMAN FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 27 these habitats came into existence. Of Aegopodium, indeed, it is stated that it is not a native species. This, however, is a view which must be reconsidered in the light of recent work on the history of the British flora (e.g. Godwin, 1950). Thus Druce, again in the Comital Flora, writes of Centaurea Cyanus L. : “Agrestal. British. Native or colonist. . . . Probably of oriental origin and perhaps native in Sicily, Greece and Cyprus”. Yet pollen of this species has recently been found in peat of Late Glacial age, both in Denmark (Iversen, 1947) and in this country (Godwin, 1949). During a visit to Sweden in the summer of 1950, all the five species listed above were seen growing as constituents of little- disturbed natural vegetation, and this prompted an enquiry into their history as members of the British flora. 1 Aegopodium podagraria L. During the excursion in Scania (S.E. Sweden), which preceded the 7th International Botanical Congress, Aegopodium Podagraria was seen on two occasions as an important constituent of the woodland ground flora. It was locally dominant in a Carpinus- Corylus wood near Stenshuvud close to the coast just north of Simrishamn, its associates being Galeobdolon luteum (f), Anemone nemorosa (f), Stellaria Holostea, Oxalis Acetosella, Allium ursi- num, Vicia sepium and Poa nemoralis. The site was damp and the soil a heavy calcareous loam. On the second occasion, it was seen in a mixed wood of Fraxinus excelsior, Ulmus glabra and Fagus sylvatica near An- drarum. Here, again on a damp calcareous soil, it was locally abundant with Polygonatum verticillatum, Geum urbanum, Fili- pendula Ulmaria, Car ex sylvatica, Geranium sylvaticum, Rubus saxatilis, Thalictrum aquilegiifolium and Equisetum sylvaticum, with Petasites albus in great quantity nearby and a few plants of Lysimachia nemorum and Car ex remota. There was no reason to doubt that Aegopodium was a natural constituent of these two woods. Lindquist (in Hubei, 1934), indeed, recognizes an Aegopodium Podagraria synusia of Swedish beech-forests, and gives its pH range as 5. 6-7. 2 ( — 7.6). Aegopodium also occurs as an occasional ground-flora species in Allin delille Fredeskov, a mixed deciduous wood in N. Sjaelland, Denmark, chiefly on cal¬ careous soil. In his valuable floristic studies of the vegetation of Lower Saxony, Tiixen (1937) recognizes a variant of the Salix alba- Populus nigra association in which Aegopodium is one of the most abundant species of the ground flora. This is a streamside woodland community, now usually persisting only in fragments, where dominant woody plants are Salix alba and various osiers, with Populus nigra and Alnus glutinosa also present. The asso¬ ciated species include many strongly nitratophilous plants such as Humulus, Solanum Dulcamara, TJrtica and Galium Aparine. 28 THE CHANGING FLORA OF HRITATN Tiixen also lists Aegopodium as a constituent of several com¬ munities of the mesophilous deciduous forests (Fagetalia sylva- ticae) and in particular of the mesophilous mixed forests (meso- phile Laubmischwalder : Fraxino-Carpinion), dominated by Quercus Robur and Carpinus Betulus or by Fraxinus excelsior and Acer Pseudoplatanus, but usually containing Fagus as well, and often as an important constituent. Using the nomenclature adopted by Tiixen, Aegopodium is a characteristic species (Ver- bandscharakterart) of the Fraxino-Carpinion and is most pro¬ minent on the moister base-rich soils, often calcareous and often gleyed below. It attains its highest constancy and abundance in those forest types which Tiixen regards as the climax commun¬ ities both on siliceous and on calcareous soils, and is more pro¬ minent in Central Germany than in N.W. Germanv. These woods are floristicallv rich, both in woody and in herbaceous species, and include a large majority of the species found in British woods on limestone, chalk and base-rich clavs. Aeaopodium also occurs in woods of the true beech zone, at higher altitudes than the oak- hornbeam and ash woods, but is there no more than an occasional component of the floristicallv richest tvpes on calcareous soils. (Markgraf, in Bubel, 1932: Diemont, 1938). In Switzerland, too, Aegopodium is found in streamside woods (Alneta incanae) and in oak-hornbeam woods of the mixed de¬ ciduous forest belt, but not in those on more definitely acid soils (Stamm. 1938). It occurs also in beechwoods on calcareous sub¬ strata: Liidi (1921) lists it on a steep scree-slope in the Lauter- brunnental at 700-830 m. above sea-level. Here the tree-layer contains Ulmvs glabra , Acer Pseudoplatanus. Fraxinus. Picea and Tilia olaUiphvUa as well as the dominant Fagus , and there are rich shrub and herb layers. But it appears to be a more constant comnonent of the mixed Tilia : woods (Tilieto-Asperuletum taur- inae), and especially of those damper tvoes in which Acer plata- noides is freouent (Trepp, 1947). These are again floristicallv rich woods on base-rich soils, and the species-list resembles that of the oak-hornbeam and beech woods in which Aegopodium occurs, though including in addition a number of warmth- demanding species. Mixed deciduous forests, with Quercus Robur, Q. petraea and Carpinus as the most important of a considerable number of tree snecies, are found throughout the lowlands of Central and Eastern Europe, and Aegopodium is a frequent component of their ground-flora, Klika (cited in Stamm, 1938) describes an example of his Querceto-Carpinetum-bohemicum and includes Aegopodium amongst the herbs: and the same author (Klika; in Bubel. 1930) records it for three forest communities at Bialowicza, Poland : Carpinetum-typicum, Carpinetum-pinosum, and Quer- eetum-sessiliflorae. Finally Keller (1927) describes a mixed de¬ ciduous forest from the Voronezh District of C. Bussia, far beyond HUMAN l1' ACTORS CONTRIBUTING TO A CHANGE IN OUR i LORA 29 the eastern limits of Fag us and Carpinus, in which it is a signi¬ ficant constituent. Aegopodium is often present in Fagus and Fagus-Carpinus forests of C. Europe, but appears to be more local in them than in the mixed forests of lower altitudes. Domin (in Riibel, 1932) does not mention it at all in his account of beech forests in Czecho¬ slovakia, but von Soo (in Riibel, 1930) gives lists which show it to be a constituent of beech and beech-hornbeam forests through¬ out the length of the Carpathians, though it is impossible from his paper to get detailed information about its associates and its habitat-preferences. While never more than occasional it attains a frequency (i.e. percentage occurrence in quadrats within the sample areas) ranging from c. 10% to c. 80%, and von Soo in¬ cludes it in his list of ‘Charakterpflanzen des Buchenwaldes in den Karpathen’. It is also included by Stoyanoff (in Riibel, 1932) amongst ‘typical and commonest representatives of the herbace¬ ous vegetation’ of Bulgarian beech-woods. Markgraf (in Riibel, 1932) and Vierhapper (in Riibel, 1932) also list it for certain beech woods in C. Germany and Austria respectively, Vierhapper classing it as characteristic of the moister beechwoods in which Fraxinus is prominent. This summary makes it clear that Aegopodium Podagraria is a natural constituent of deciduous forest on base-rich soils throughout Europe from south Sweden, north-west Germany and Switzerland, eastwards to central Russia, apparently being most prominent in moist Eichenmischwalder and in valley-bottom and stream-side woods, especially in central and eastern Europe. It is also found in beechwoods, and occasionally in coniferous woods. In north-west Europe, however, Aegopodium is by no means confined to forests. Tiixen (1937) includes it in his list of a com¬ munity characteristic of the sides of streams and ditches on heavy nitrogen-rich soils (Cirsium oleraceum- Angelica sylvestris Associa¬ tion, Sub-Association of Petasites hybridus). The ecologically most significant species of this community are Petasites hybridus, Urtica dioica, Anthriscus sylvestris, Dactylis glomerata, Angelica sylvestris, Filipendula Ulmaria, Aegopodium Podagraria and Glechoma hederacea. The same author lists Aegopodium as an important constituent of two ruderal communities of the Cheno- podietalia medio-europaea, both included in the Arction lappae. One of these, the Chaerophyllum bulbosum Association, is found where Salix alba, Populus nigra, etc., have been cleared from stream-valleys in country where oak-hornbeam woods form the natural vegetation. Besides Chaerophyllum bulbosum and Aego¬ podium other prominent species are Carduus crispus, Urtica dioica, Artemisia vulgaris, Myosoton aquaticum, Calystegia sepium, Galium Aparine and Rumex obtusifolius. The other is called by Tiixen the Chenopodium Bonus-Henricus — Urtica urens Associa¬ tion, and is a strongly nitratophilous and very widespread weed- community in which Lamium album, Urtica dioica, Plant ago THE CHANGING FLORA OF BRITAIN ;u) major, Poa annua, Rumex obtusifolius, Malva neglecta, and Tarax¬ acum officinale are other prominent species. These or closely simi¬ lar communities are known in large parts of Europe, including this country, and it is the frequency with which Aegopodium occurs in them that gives it its reputation as being primarily a weed. Its true status has been further obscured by its tendency to bulk largely in the vegetation of woods in which human interference has been considerable. Thus Domin (1928), in a list of species in a Carpinus-Corylus wood in the Valley of Radotin, near Prague, divides the ground-flora herbs into ‘wood-herbs’ and herbs of a weed character, the latter including Aegopodium, Anthriscus syl - vestris, Chaerophyllum temulum, Galium Aparine, Geum urbanum, Campanula rapunculoides , Chelidonium majus and Taraxacum officinale. But there are no good grounds for doubting that Aegopodium is a genuine constituent of undisturbed deciduous woodland in many parts of Europe, and the same may well be true of all the species in Domin’s list. % In the British Isles Aegopodium is an abundant hedgerow plant in the neighbourhood of villages, conspicuous northwards at least to central Scotland; and is too well known as a pernicious weed of gardens and shrubberies, difficult to extirpate because of its numerous and brittle stolons. Not infrequently it becomes prominent in open scrub and streamside swamp-woods near human dwellings, but I have never seen it looking other than secondary in such localities. I have, however, found it in ash-elm woods in the Evenlode valley, in Oxfordshire, on the deep moist colluvial soils at the foot of limestone slopes, and I can see no good reason for doubting that it may be native there. Horwood and Gainsborough, in their Flora of Leicestershire and Rutland (1933), write : “As this plant occurs in damp oak wood and in ash oak wood, it may be considered native”, and authors of other county floras make similar statements. The similarity of these habitats to some of those in which Aegopodium seems undoubtedly native in continental Europe strengthens the case for regarding it as native also in this country. I am informed by Dr. H. Godwin that Miss Allison has found fruits of Aegopodium on a Roman site at Cottenham, near Cambridge. The significance of this find is made somewhat doubtful, however, by the fact that Aegopodium was long used in various parts of Europe as a green vegetable and as a medicinal plant with a great reputation especially for curing gout. It has certainly been cultivated for these purposes and might have been introduced to the country during the Roman occupation, but its general continental distribution and habitat- preferences seem in favour of the view, put forward here, that it has been a constituent of our native flora at least since the estab¬ lishment of mixed oak forests in the south. 2. Chaerophyllum temulum L. Chaerophyllum temulum resembles Aegopodium in its Euro¬ pean distribution but extends less far north, having only a handful HUMAN FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA ;n c-f localities north of 60° N. in Sweden and Finland, and being absent from northern Russia. Nor does it attain the importance of Aegopodium as a constituent of woodland floras in central and eastern Europe. Tiixen (1937) includes it in his list for the Fagetum boreo-atlanticum allietosum ursinae, beechwoods on moist calcareous substrata in north-west Germany, its constancy being 12%. It occurs also with about the same constancy in the Cicerbita alpina sub-association of Tiixen’s Acereto-Fraxinetum, a community in which Acer Pseud oplatanus, Picea, Fraxinus and Fagus constitute the tree-layer and which occurs on moist slopes in the Harz Mts., in the upper part of the Fagus zone. Its rich and luxuriant herb layer resembles that of certain subalpine woods in the mountains of Central Europe. Chaerophyllum is also listed for the related streamside ashwoods in the middle and upper Fagus zones which Tiixen has named Cariceto remotae — Fraxi- netum chrysosplenietosum, though here its constancy is only 5%. It is also a “Charakterart” of Tiixen’s Querceto-Carpinetum medioeuropaeum but is a significant constituent only of the moister sub-associations and especially of those beech-hornbeam- oak woods on calcareous or circumneutral soils in which Aegopo¬ dium also attains its maximal abundance. Markgraf (in Riibel, 1932) records it for two Mercurialis- beechwoods in Central Ger¬ many, and Domin (in Riibel, 1932) for mixed Fagus- Acer -Ulmus woods in the west Carpathians whose chief ground-flora species are Galeobdolon, Glechoma hirsuta and Asperula odorata. It is rare in Austrian beechwoods, not recorded by Meusel (1935) in the oak and oak-hornbeam woods of the Grabteld nor by Stamm (1938) in oak-hornbeam woods of Switzerland, listed by Domin (1928) as one of the ‘herbs of a weed-character’ in a Carpinus-Corylus wood near Prague, and by Klika (1930) as a constituent of Carpinetum typicum at Bialowicza in Poland. The general impression given by these records is that Chaero¬ phyllum temulum is a rather unimportant natural constituent chiefly of moist deciduous woods on base-rich substrata, often associated with Aegopodium but absent from the drier woods in which that species occurs. Like Aegopodium, Chaerophyllum temulum is conspicuous in certain ruderal and semi-ruderal communities. Tiixen (1937) assigns it a constancy of c. 20% in a widespread community of clearings in moist Querceto-Carpineta, the Epilobium angusti- jolium-Senecio sylvaticus association of the Atropion, sub-associ¬ ation of Deschampsia caespitosa; and it is still more prominent in the nitrophilous shade-loving weed-community of hedges, wood-margins, etc., which he terms the Alliario-Chaerophylletum temuli (Tiixen, 1950) and whose most important constituents are Alliaria, Chaerophyllum temulum, Lapsana communis, Bryonia dioica, and Viola odorata. In the British Isles Chaerophyllum temulum is a plant of hedgerows and wood-margins on better soils through much of the country, though absent from some of the northernmost vice- THE CHANGING FLORA OE BRITAIN 52 counties and much less common in Scotland than Aegopodium. It is occasionally found in woods in circumstances suggesting that it may be an original constituent of the ground-flora, but much more generally it is a human associate. I can find no record of its use as a food plant ; it has, indeed, been described as poison¬ ous to stock. But it was certainly used medicinally and Hegi (1908-31) states that it was planted in German gardens, ap¬ parently for this purpose, around 1560. Fruits of Chaerophyllum temidum have been recorded from interglacial beds at West Wittering, Sussex (Reid, 1899). 3. Anthriscus sylvestris (L.) Bernh. Of the three umbellifers included in this enquiry, Anthriscus sylvestris is certainly the most widespread, the most abundant and the one whose original ecological status is the most evident. While Aegopodium and Chaerophyllum temidum can be regarded as native no further north than Central Sweden, Anthriscus ex¬ tends to the shores of the Arctic Ocean and throughout Scan¬ dinavia as a clearly natural constituent of communities which have suffered little or nothing from the hand of man. Important works by Nordhagen (1928, 1943) and Kalela (1939) provide a great deal of information about its role in Scandinavian vegeta¬ tion. In the mountains of Norway, Anthriscus sylvestris is charac¬ teristic of the tail-herb communities of base-rich habitats which are grouped by Nordhagen (1943) into his Mulgedion alpini, though it occurs in a wider range of communities at lower levels. The Mulgedia alpini are found either as woodland ground-flora communities, or associated with shrubby willows, or in subalpine meadows with no associated woody plants; and Anthriscus oc¬ curs in all three situations. It has a constancy of 33 % in sub¬ alpine birch-woods of Betula tortuosa at c. 1020-1100 m. above sea-level in Sikilsdal (Nordhagen, 1943), its chief herbaceous asso¬ ciates being Aconitum septentrionale , Geranium sylvaticum , Saus- surea alpina, and, more locally, Mulgedium alpinum ( Cicerbita alpina), with Alchemilla vulgaris agg., Angelica sylvestris, Chamaenerion angustifolium, Cirsium heterophyllum, Equisetum pratense, Filipendula Ulmaria, Geum rivale, Gnaphalium norvegi- cum, Melandrium dioicum, Myosotis sylvatica, Polygonatum ver- ticillatum, Ranunculus acris, Ruhus saxatilis, Rumex Acetosa, Solidago Virgaurea, Trientalis europaea amongst the other herbs present. Further north Trollius europaeus, Stellaria nemorum, and Viola biflora become important constituents, and Anthriscus is more prominent. Birchwoods of this type were seen on moun¬ tains in Swedish Lappland, west of Abisko, and the components of the herb layer, including Anthriscus, extended above the woods into scrub of Salix lanata and other willows, and locally formed subalpine meadows above the willow belt. Kalela (1939) de¬ scribes ‘Hochstaudenwiesen’, of essentially the same composition, as characteristic of the more base-rich soils in the ‘arctic’ zone, HUMAN FACTORS CONTRIBUTING TO A CHANGE IN OUR FLORA 33 north of the tree-limit, in the Fischer Peninsula of northernmost Finland. They are regarded as truly spontaneous and are de¬ veloped most typically on steep sunny slopes and on screes and only where the snow melts early. The most demanding of these communities, found on moist calcareous slopes, is dominated by Anthriscus sylvestris and Angelica Archangelica, with Geranium sylvaticum, Rumex Acetosa, Stellaria nemorum, Viola biflora , Milium effusum, and Trollius europaeus as other species of high constancy. This is the most productive community of the area, often attaining almost 2 m. in height. Manuring by sea-birds increases its luxuriance locally. Anthriscus is also prominent in Kalela’s Geranium sylvaticum-Wiese (with Geranium sylvati¬ cum, Viola biflora, Trollius europaeus, Alchemilla vulgaris agg., Rumex Acetosa, Chamaenerion angustifolium and Filipendula Ul- maria as species of highest constancy), but less so in other related Hochstaudenwiesen, though fairly well represented in some rela¬ tivity oligotrophic communities characterized by the abundance of Athyrium Filix-femina and Cicerbita alpina. Elsewhere in Europe Anthriscus appears to play no very im¬ portant part in woodland communities, though it is occasionally listed for high level beechwoods on base-rich soils, as by von Soo (1930) for certain woods in the east Carpathians. But it is wide¬ spread and locally very abundant in the rich grassland communi¬ ties (Fettwiesen) which have often replaced forest at all levels from valley-bottoms to the tree limit. These communities fall into two main groups, the Arrhena there ta and Triseteta, character¬ ized by the grasses from which they are named, the latter com¬ monly at higher levels than the former. Anthriscus is a con¬ spicuous component of all the types of grassland in which grazing is not very heavy, and especially of those which are mown first and grazed only towards the end of the season : it is most luxuriant where the grassland is dunged. Apart from these meadows Anthriscus sylvestris is also a prominent constituent of the luxuriant stream and ditch-side com¬ munity which Tiixen names the (Cirsium oleraceum — Angelica sylvestris Association, Sub-Association of Petasites hybridus’, and which has already been mentioned (p. 29) in connection with Aegopodium. In this country Anthriscus sylvestris lines our roads and fields over wide areas where the substratum is at least moderately base- rich, becoming a highly characteristic feature of hedgerows in April and May. It invades mowing-grass but is kept down by continuous grazing and so is rarely an important constituent of pastures. It is frequent on the drift-lines of rivers and brackish marshes, but I have so far been unsuccessful in my attempts to find it on those high rocky ledges and terraces, protected from in¬ tensive grazing by at least a partial inaccessibility to sheep, where flourish Trollius, Chamaenerion, Geranium sylvaticum, Rumex Acetosa, Ranunculus acris and many other late Glacial relicts. I have sought for it in vain on Ben Lawers and neighbouring hills, c 34 THE CHANGING FLORA OF BRITAIN on Lochnagar, in Glen Canness and in Caenlochan Glen. I shall be much interested to know whether any readers have seen it in such places, or in mountain birchwoods in Scotland. If it is really absent from such localities, it would be premature to regard it as a Late Glacial survivor, even though its absence might be the result of comparatively recent climatic change. It is perhaps significant that the common form in the north of Great Britain (var. angusti- secta (Druce)) is somewhat different from the southern form, more glabrescent, with more finely dissected leaves and larger fruit. It is said to extend southwards to Derbyshire, and it is a possible inference that this is the old indigenous form, the southern plant (var. latisecta (Druce)) having immigrated at a later date and per¬ haps through human agency. But further study is required of its morphological distinctness, and of its distribution inside the country and elsewhere, before such speculations can have real value. Anthriscus sylvestris is eaten by cattle and rabbits and, ac¬ cording to Church (1925) has been used as a pot-herb. It has been recorded from Interglacial beds at West Wittering, Sussex (Reid, 1899). 4. Tanacetum vulgare L. Tansy is a locally important component of the Geranium sylvaticum- meadows described by Kalela (1939) from the Fischer Peninsula in northernmost Finland. These occur chiefly on sunny scree and detritus -slopes below cliffs or on stream-banks. Ger¬ anium sylvaticum and Trollius europaeus are the dominant species, and Chamaenerion angustifolium , Poa nemoralis and Anthriscus sylvestris are conspicuous. Tanacetum also occurs in a community dominated by Chamaenerion on the sandy bank of the Pummanginjoki river. Here Deschampsia caespitosa, Rumex Acetosa, Trollius, Ranunculus acris, Alchemilla vulgaris agg., and Geranium sylvaticum are its chief associates. Further south, Tanacetum is listed by Almquist (1929) for several maritime and lake-shore communities in Uppland. It is regarded by him as indigenous in these habitats, and especially on the numerous islets off the coast. Amongst the most interest¬ ing of the communities on these ‘skerries’ are those dominated by Hippophae rhamnoides, of which Tanacetum is a frequent and often a prominent constituent. It occurs also in open wind- dwarfed Juniperus scrub on moraine with a great variety of as¬ sociated grasses and herbs. In one such example (Kallskar) the main species were Juniperus communis, Chamaenerion angusti¬ folium, Origanum vulgare, Festuca ovina and F. rubra, Tanacetum vulgare, Agrimonia Eupatoria, Cirsium palustre, Galium verum, Dryopteris Filix-mas and D. spinulosa, with Cladonia spp. Yet again, Tanacetum is often in Uppland on maritime cliffs. One list (Kalmar; Getberget) includes Tanacetum with Berberis vul¬ garis, Cotoneaster integerrima, Rosa Afzeliana, Calluna, Artemisia campestris, Asplenium septentrionale, Calamintha Acinos, Clino- HUMAN J-AUTORS CON TR1B U TIN G TO A CHANGE IN OUR FLORA 35 podium vulgare, Cynanchum vincetoxicum, Geranium sangui- neum , Polygonatum officinale, Potentilla argentea, Sedum Tele- phium, Veronica spicata, Woodsia ilvensis, etc. These are all communities which have suffered little disturb¬ ance from man. Tanacetum is also a feature of species-rich maritime grasslands which may owe their freedom from woody plants in part to grazing, though exposure is undoubtedly the chief determining factor and is apparently the only one on some of the smaller islands. These ‘maritima ortsbackakr’ are com¬ monly tall-growing and their chief constituents are Arrhenathe- rum, Avena pubescens, Agrimonia Eupatoria and A. odorata, An- thriscus sylvestris, Chamaenerion, Hypericum perforatum, Ori¬ ganum, Veronica longifolia and Tanacetum. Lastly, Tanacetum is widely spread, in Uppland, in gardens, hedgerows, field-borders, railway-embankments, etc., and is often cultivated, so that it is sometimes difficult or impossible to distin¬ guish between native and secondarily established plants. Passing southwards from Uppland to north-west Germany, we find that Tiixen (1937) gives Tanacetum as a significant com¬ ponent of various drift-line communities by rivers, lakes and the sea. These include a maritime Atriplex litt oralis association, in which Atriplex spp., Matricaria maritima, Cakile and Salsola are the most constant constituents; and a Bidentetum tripartiti, of riverside flats, characterized by Atriplex hastata, Chenopodium rubrum, Bidens tripartitus, Rorippa spp., Polygonum spp., Rumex spp., etc. It is also recorded as attaining about 30% con¬ stancy m two more definitely ruderal communities, the Cheno¬ podium Bonus-Henricus — Urtica urens and Hordeum murinum associations, the former with Lamium album, Urtica dioica, Plan- tago major, Urtica urens, Poa annua, Chenopodium Bonus-Henri¬ cus, Rumex obtusifolius and Malva neglecta; the latter with Hordeum murinum, Capsella Bursa-pastoris, Sisymbrium officin¬ ale, Lolium perenne, Polygonum aviculare, Taraxacum officinale, and Artemisia vulgaris as the species of highest constancy. In a later classification of nitrophilous ruderal communities Tiixen (1950) recognises a Class Artemisietea vulgaris of which Tanacetum is one of the characteristic species. The Class con¬ sists of perennial nitrophilous herbaceous communities of drift¬ lines, hedgerows and wood-margins and of waste places through¬ out the whole of the Eurosiberian region of Europe, excluding only the alpine and subarctic zones. But Tanacetum may also attain a fairly high constancy in communities of at least two others of the Classes recognised by Tiixen, the Cakiletea mari- timae and the Bidentetea tripartiti, so that it is clearly a con¬ spicuous and very widespread constituent of these nitrophilous assemblages. Of special interest in this connection is the paper by Nord- hagen (1940) on the plant communities of drift-lines in Norway. Brackish lagoons in south Norway have a luxuriant drift-line vegetation which is commonly dominated by Filipendula Ulmaria, ;3G THE CHANGING FLORA OE BRITAIN though Euphorbia palustris or Festuca pratensis may dominate where the substratum is stony. Tanacetum is often associated both with Filipendula and with Euphorbia palustris. Nordhagen expresses the view that these drift-lines are ancient and wholly natural habitats and that many common ruderals may well have spread from them when man opened up comparable habitats in and around his settlements. The brackish drift-lines mentioned above support many other species which we now regard as rude¬ rals: Agropyron repens, Potentilla Anserina, Rumex crispus, Sonchus arvensis, Calystegia sepium, Artemisia vulgaris, Cir- sium arvense, Equisetum arvense, etc. It may be concluded that Tanacetum vulgare is probably a natural component of certain maritime, lake-shore and riverside communities, and especially of drift-lines, throughout much of north-west Europe. It is also a widespread ruderal and has been further favoured by its frequent cultivation. 5. Tussilago Farfara L. Coltsfoot, like Tansy, reaches the extreme north of Scandin¬ avia and is included in Kalela’s list (1939) for Chamaenerion angustifolium meadows in the Fischer Peninsula, where it is asso¬ ciated with Anthriscus sylvestris and Tanacetum in a community dominated by Chamaenerion and with Trollius, Geranium sylva- ticum, Rumex domesticus, R. Acetosa, Ranunculus acris and Solidago Virgaurea. I have seen it in essentially similar com¬ munities in and just above birchwoods near Abisko in Swedish Lappland. But its most characteristic habitats throughout Scan¬ dinavia are the calcareous seepage-fens dominated in the north and on mountains by Saxifraga aizoides, Epilobium alsinifolium and tufa-forming bryophytes, and in lowland localities in the south by J uncus subnodulosus. In Uppland Almquist (1929) reports Tussilago locally on mari¬ time sand and shingle, and as an occasional ground-flora species of certain Picea woods on moist base-rich drift soils. Sterner (1938) regards it as probably indigenous in Oland by streamlets (in the forest or otherwise) and on the drift-line amongst boulders. Both these writers record it also in many secondary habitats. Nordhagen (1940) lists it in drift-line vegetation in two localities in south-west Norway, and Hard av Segerstad describes it as native in seepage-fens, by streams and perhaps on the banks of rivers. Tiixen reports Tussilago as occurring in about one in four of the samples of a community characteristic of felled areas in decid¬ uous woodland on heavy calcareous soils in S. Hanover, a variant of the Atropetum belladonnae with abundant Calamagrostis epigeios; and, more constantly, in a widespread ruderal com¬ munity, on similarly heavy base-rich soils, in which Chenopodium spp., Polygonum spp., Sonchus spp., Senecio vulgaris, Capsella Bursa-past oris, Equisetum arvense, and Ranunculus repens are prominent. human factors contributing to a change in our flora 37 Turning to this country we find that Gerard (1597) says of coltsfoot that ‘This groweth of itselfe neere unto springs and on the brinkes of brookes and rivers, in wet furrows, by ditches sides, and in other moist and waterie places neere unto the sea almost every¬ where’, and it is not easy to improve on this statement. It is familiar enough as a weed on clays and heavy loams, luxuriating in base-rich and well-manured soils and often becoming a really per¬ nicious weed. But it is also an abundant colonist of boulder-clay banks and cliffs and of drift-line vegetation. And it is frequent at seepage-zones and in the water-washed turf or amongst the boulders by streamlets at all levels to 3,500 ft. or so on our base- rich hills and mountains. I have seen it for instance at seepage- zones between Malham Tarn and Arncliffe and in many spots high up on Ben Lawers and neighbouring hills, and here its native status cannot be doubted. Coltsfoot, as its Latin name implies, was for long used as a medicinal plant and may occasionally have been planted for that purpose, though we need hardly to suppose that its spread would have been much less than at present had it never been planted. It is of interest that it has been recorded from Post-Glacial beds at Redhall, near Edinburgh (Reid, 1898). Discussion. We see, then, that all these five species may very reasonably be regarded as ancient inhabitants of this country. All occur as un¬ doubted natives of neighbouring continental areas, all have been considered as at least probably native in some of their British localities, and for all of them their distribution and habitat- preferences on the European mainland make it a very reasonable inference that they have been in this country since before the beginning of the historical period. For three of them, Anthriscus, Tanacetum and Tussilago, it seems probable that they became widespread here during the Late Glacial times, since they are constituents of subalpine and near-arctic vegetation in northern¬ most Scandinavia, though Anthriscus may have flourished more particularly in the birchwoods of a slightly later date. The other two, Aegopodium and Chaerophyllum, are more warmth- demand¬ ing and more definitely woodland plants which would not have found optimal conditions until the spread of the mixed oak-forests of late Boreal and Atlantic times. All could have colonised drift¬ lines and banks by streams, rivers, lakes and the sea-shore, and all would have been available for, and capable of spread into, forest-clearings made by Neolithic and later man. They are all vigorously growing perennials with a strong capacity for vegeta¬ tive spread, all are nitratophilous and all react in a highly favour¬ able manner to nitrogenous manuring, and so all would become prominent constituents of the vegetation in the vicinity of human settlements. There they would attract attention as potential foods or medicines and might be introduced more widely on that account or unintentionally in carried fodder. Wayside banks and 38 THE CHANGING FLORA OF BRITAIN hedgerows persist to the present time as habitats providing the requisite conditions of base-rich, actively nitrifying soils, often with the light shade, which the three umbellifers seem to favour, and usually with protection from extremes of grazing and tramp¬ ling to which such tall-growing herbs are susceptible. And, in some localities, drift-lines also persist as relict habitats in which the species have been able to survive. We have still to consider why the species under consideration have so nearly disappeared from what seem to be their original woodland habitats. The chief factors operating here are clearly the replacement of so large a proportion of woodland on the better types of soil by arable land or grassland, and the mode of manage¬ ment of the residual woodland areas. The British Isles have suffered much heavier losses of their natural woodlands than most other European countries and much of what remains is on the poorer types of soil. Such ‘better’ woodland as does survive is almost all either coppiced or grazed, both modes of management inimical to tall-growing herbs. It is possible that climatic changes in early historic time have also operated adversely on some of the species. These problems cannot easily be solved until investigations such as those of Dr. Godwin and his collaborators have yielded more positive information about the early history of our British flora and about these hedgerow plants in particular. Meanwhile I can heartily recommend, as a valuable and fascinat¬ ing study, attempts to elucidate the status of the many other components of our wayside and hedgerow vegetation. BIBLIOGRAPHY. Almquist, e., 1929, Upplands vegetation och flora, Acta Phytogeogr. Suecica, 1. Uppsala. Church, A. H., 1925, Introduction to the Plant-Life of the Oxford District. II. The Annual Succession. Oxford University Press. Diemont, W. H., 1938, Zur Soziologie und Synoekologie der Buchen- und Buchen- mischwalder der nordwestdeutschen Mittelgebirge, Mitteil. d. Flor.- soziol. Arbeltsgemeinschaft in Niedersachsen, 4. Gerard, John, 1597, The Herhall or Generali Historie of Plants. London. Godwin, H., 1949, The spreading of the British flora considered in relation to con¬ ditions of the Late-Glacial period, J. Ecol., 37, 140-147. Druce, G. C., 1932, The Comital Flora of the British Isles. Arbroath. Hegi, G., 1908-1931, Illustrierte Flora von Mittel-Europa, Miinchen. Iverson, j., 1947, Centaurea cyanus-pollen in Danish Late-Glacial deposits, Meddelels. f. Dansk Geol. Foren., 11/2, 197-200. Kalela, A., 1939, Uber Wiesen und wiesenartige Pflanzengesellschaften auf der Fischerhalbinsel in Petsamo Lappland. Acta Forestalla Fennlca, 48/2, 1-523. Keller, b., 1927, Distribution of vegetation on the plains of European Russia, J. Ecol., 15. LUdi, W., 1921, Die Pflanzengesellschaften des Lauterbrunnentales und ihre Sukzession, Beitr. z. geobot. Landesaufn., 9, 1-364. Meusel, H., 1935, Die Waldtypen des Grabfelds und ihre Stellung innerhalh der Walder zwischen Main und Werra, Beih. Bot. Centralbl., 53, B, 1. Nordhagen, R., 1928, Die Vegetation und Flora des Syleneg ebietes . I. Die Vege¬ tation. Oslo. - , 1940, Studien fiber die maritime Vegetation Norwegens, I. Die Pflanzen¬ gesellschaften der Tangw&lle, Berg. Mils. Arbok, 1939*1940: Nature, rekke, 2- HUMAN FACTORS CONTRIBUTING TO A CHANCE IN OUR FLORA 39 - , 1943, Sikilsdalen og Norges Fjellbeiter. Bergen. Reid, Clement, 1899, The Origin of the British Flora. London. RUbel, E., 1930, Ergebnisse der Internationalen Pflanzengeographischen Exkur- sion durch die Tschechoslowakei und Polen 1928, Veroffentl. d. geobot. lnstit. Riibel in Zurich, 6- - , 1932, Die Buchenwalder Europas. Verdffentl. d. geobot. lnstit. Riibel in Zurich, 8- Stamm, E., 1938, Die Eichen-Hainbuchen-Walder der Nordschweiz, Beitr. z. geobot. Landesaufn. der Schweiz, 22, 1-163. Sterner, R., 1938, Flora der Insel Oland, Acta Phytogeogr. Suecica, 9. Uppsala. Trepp, W., 1947, Der Lindenmischwald (Tilieto-Asperuletum taurinae), Beitr. z. geobot. Landesaufn. der Schweiz, 27, 1-128. Tuxbn, R., 1937, Die Pflanzengesellschaften Nordwestdeutschlands, Mitteil. d. Flor.-soziol. Arbeitsg emeinschaft in Niedersachsen, 3. - , 1950, Grundriss einer Systematik der nitrophilen Unkrautgesellschaften in der Eurosibirischen Region Europas, Mitteil. d. Flor.-soziol. Arbeits- gemeinschaft in Niedersachsen, N.F., 2 This paper was discussed as follows : — Mr. Mf.ikle stated that he had seen Anthriscus sylvestris on moun¬ tain cliffs in Ireland. It grows in considerable quantity at about 2000 ft. altitude on the damp cliffs above Lough Muskry in the Galtee Moun¬ tains, S. Tipperary. Here it is associated with woodland plants such as Melandrium dioicum (L.) Coss. & Germ, and Orchis mascula L., montane species such as Saxifraga stellaris L., Oxyria digyna (L.) Hill, etc., and with Saxifraga rosacea Moench and S. spathularis Brot. Dr. Watt stated that in Aberdeen coltsfoot was widely used as a substitute for tobacco, and known generally as “ Tussilago.” He thought it was worthy of note that all five species reviewed by Prof. Clapham favoured habitats which, judging from the associated species, are strongly nitrifying; such associations are likely to be extended by human activities. Prof. Olapham replied that the strong response of the five species to nitrogen was likely to be responsible for their attracting human attention. Man was likely to find uses for plants brought so pro¬ minently to his notice. Dr. Dahl remarked that the best criterion we have that a species is natural in a country and not introduced by man is undoubtedly whether it is established in natural communities. One should be care¬ ful, however, not to press this criterion too far. Thus we have his¬ torical record of the introduction of Senecio viscosus L., but it is nevertheless established in perfectly natural communities along sea¬ shores just as well as Tanacetum vulgare L. and Tussilago Farfara L. Dr. Butcher suggested that the two varieties of Anthriscus sylnes- tris which had been mentioned seemed to provide an opportunity for somebody to do some biometrical research. Following a question from Dr. Walters, Dr. Dahl stated that on the introduction of agriculture into Scandinavia, the weeds were ap¬ parently recruited from two main natural vegetation types besides those man brought with him. One was the nitrophilous seashore com¬ munities, the other the tall herb communities essentially of subalpine, northern and continental types. In the south and west these are re¬ placed by fern communities. 40 THE CHANGING FLORA OF BRITAIN POSSIBLE HUMAN HISTORICAL FACTORS DETERMINING THE DISTRIBUTION OF ERIOPHORUM LATI FOLIUM IN THE NORTH¬ WEST CONWAY VALLEY (Exhibit) R. Elfyn Hughes. The choice of site for utilisation and occupation by man at any stage in the human settlement of a region is largely deter¬ mined by : a. the level of civilisation of the community as reflected in its technical ability. b. factors that are essentially ecological. (East (1935), Gradman (1931), Grimes (1945), and Mutton (1938)). Human settlement has been studied in the north-west Conway Valley (Hughes (1940, 1949b)). It has been shown that terrains characterised by basic igneous rocks (augite dolerite pumice tuffs, and spilitic agglomerates) — occurring either as outcrops or as major constituents of the glacial drifts, have been foci of human settlement at various periods in the past. These terrains are also foci of intense interference with the native vegetation. Within “basic” terrains, local drainage conditions, in particular, have an important influence on site selection by man. The collation of documentary and field evidence shows that, as one would expect, “basic” terrains with a preponderance of free-draining sites at altitudes of 700-1,000 ft. were occupied during the mediaeval period, while extensive areas of impeded drainage were occupied mainly in the 16th century. More difficult country at higher altitude was enclosed or occupied subsequent to the 16th century (sporadic “squatter” movement) and during the 19th century (statutory enclosure). Soils of impeded drainage, particularly those which are peaty and derived from the “basic” drifts, bear a Molinietum of eutro- phic affinities1, of subseral origin from upland alderwood. (The floristic composition of the community is given in Table I). Eriophorum latifolium, a species atypical of western Britain, is present sporadically in this community in the Conway Valley. The peats on which it occurs are moderately acid, and of a high nutrient status (table II). These soils are discussed in greater detail elsewhere (Hughes (1949a)) — and have affinities with fen peat. This cotton grass appears to be sensitive to anthropogenic influences. Therefore, since it occurs within “basic” terrains, the foci of major human interference at different periods in history — i The central group of species within the community are primarily eutrophic though some other species reflect a tendency to oligotrophism (e.g., Sphagnum spp. and Eriophorum angustifolium). PLATE I lloyal Air Force, Crown Copyright reserved. Valley A. \ alley 13. Human Settlements of Valleys A and 11. For key, see p. 45. PLATE II. Royal Air Force, Crown Copyright reserved. Human Settlement of Valley C. 45. For key, see p. DISTRIBUTION OF ERIOPHORUM LATIFOLIUM 41 the study of its distribution and ecology in the Conway Valley provides tentative evidence of the influence of past and con¬ temporary anthropogenic factors on the distribution of a species. On edaphic grounds the potential distribution of E. latifolium in the Conway Valley is greater than at present. Thus, potential habitats for the species are found in three major lateral valleys, A. (Porth llwyd), B. (Dulyn) and C. (south branch of Tafolog), but it is not found in A. The soils of the three valleys are of similar origin, being derived from “basic” drifts, but they differ in the general features of their topography, such that the pre¬ valence of soils of free drainage is in the following order: A>C>B. Documentary evidence shows that valley A was extensively oc¬ cupied in the mediaeval period ; C, to a limited extent during the mediaeval period, while the major part of it was enclosed and occupied in the 16th century with extensions to higher altitudes in subsequent centuries. In valley B, major occupation occurred in the 16th century with marginal earlier occupation, with post- 16th century expension at higher altitudes. The present-day intensity of summer grazing shows the same trend. Much of valley A will carry up to 5 ewe units to the acre, valley C is variable, with local areas carrying 5 (free draining soils) and others about 1.5 (wetter soils) ewe units to the acre.2 Valley B carries about 1.5 ewe units to the acre. It is, therefore, evident that since mediaeval times anthropogenic influences have been greater in A than in C and in C than B. It is tentatively suggested that this has an important bearing on the present-day distribution of E. latifolium in the three valleys. This species is absent in the eu trophic Molinietum of valley A, because it has been subject to intense anthropogenic influences from the mediae¬ val period — this continues to-day in the form of heavy grazing. On the other hand in valley B, E. latifolium occurs extensively, since it was occupied at a later period (16th century), subject to less intense settlement, and a lower grazing intensity to-day. Valley C occupies an intermediate position, as it was partly occupied in the mediaeval period and partly in the 16th century, and present-day intensity of grazing is variable, so that E. lati¬ folium is of limited occurrence, though its potential range is greater. The relevant details are set out in the aerial photographs (Plates I and II) and below. Valley A (Porth llwyd). The extensive human settlement of the valley is clearly evident in the photograph, and sites of mediaeval occupation are prevalent. Early settlement here is primarily due to the pre¬ valence of soils of free drainage. Eutrophic Molinietum occurs 2 Grazing intensity of all livestock is expressed In terms of a common ewe unit (vide Watson & Moore; 1949, Agriculture : The Science and Practice of British Farming, p. 795; London). 42 THE CHANGING FLORA OF BRITAIN in small hollows and along seepage lines, and is distinctly more anthropogenic than its equivalent in the other two valleys — i.e. the Molinia is shorter and more closely grazed (5 ewe units/ acre), and there is a greater prevalence of Holcus lanatus and Ranun¬ culus acris. Note the absence of E. latifolium sites. Valley B (Dulyn). The pre-mediaeval phase of settlement bears no relationship to the problem discussed here; details are presented elsewhere (Hughes (1940)). Major mediaeval settlement is confined to the south side of the valley — selecting outcrops of basic igneous rocks (I). Note the 16th century spread to acidic terrain (rhyolite) with a heath vegetation (II) and to glacial drift with impeded drainage (III) bearing an eutrophic Molinietum. The north side of the valley was occupied mainly in the 16th century. Here peaty soils abound, and bear an eutrophic Molinietum in which E. latifolium is frequent.3 The Molinia here is less heavily grazed (intensity 1.5 ewe units /acre) and is taller than in valley A. Here grazing intensity appears to be the optimum for the survival of E. latifolium. Any change in land utilisation leading to heavier stocking in summer, or a change in drainage conditions, would probably lead to the partial or total elimination of this species. Valley C. Here we have more intensive mediaeval occupation than in valley B. Note the occurrence of E. latifolium within an area of 16th century enclosure, and where grazing intensity has re¬ mained comparatively low (1.5 ewe units /acre). High level 16th century occupation has occurred in relation to the prevalence of basic igneous rocks on the flanks of Peny Gader (I). Post 16th century (“squatter” movement) and 19th century enclosure (II) occur at higher altitudes, and at lower altitudes on parts of the glacial drift which bears a Nardetum (gley pod- solic soils) (III). Conclusions. The most important factors which determine the presence of E. latifolium in the Conway Valley are primarily edaphic — these depending on the presence of basic igneous rocks in the district. Its distribution with the eutrophic Molinietum in which it occurs, appears to be dependent on past and present-day intensity of anthropogenic factors. The Molinietum of areas occupied in the mediaeval period, and still heavily grazed, bear no E. latifolium. But areas occupied initially in the 16th century and but lightly grazed, harbour abundant E. latifolium. The importance of these considerations in the conservation of the species is stressed. 3 This side of the valley was described as alderwood in the 16th century. DISTRIBTTTION of eriophorum latifolium 43 Table I. Floristic Composition of the Eutropic Molinietum. (Number of sites studied =41). Constancy 5 Molinia caerulea a. to co-d. Juncus acutiflorus a. to co-d. Agrostis sp. f. la. Constancy 4 Holcus lanatus f. la. Anthoxanthum odoratum f. Festuca rubra f. Festuca ovina o. Potentilla erecta o. f. If. Constancy 3 Briza media o. f. la. Carex echinata f. Lotus uliginosus o. f. If. Luzula multiflora var. congesta o. f. Carex panicea f. la. Succisa pratensis f. Narthecium ossifiagum o. If. Sphagnum sp. f. la. Those species in the lower constancy groups include species of — non-acid peat species, e.g. Eriophorum latifolium (2. o. la.) Schoenus nigricans (1. If.) acid peats, e.g. Eriophorum angustifolium (2. o. la.) Trichophorum caespitosum (1. lo.) Juncus squarrosus (1. lo.) Nardus stricta (2. o.) wet soils generally, e.g., Cirsium palustre (2. o.) Hydrocotyle vulgaris (2. o.) Achillea ptarmica (1. lo.) heath, e.g. Vaccinium Myrtillus (1. lo.) Ulex Gallii (1. lo.) non-exacting species of agricultural grassland, e.g. Cynosurus cristatus (2. o. lo. f.) Plantago lanceolata (1. lo.) Luzula campestris (1. lo.) exacting species of agricultural grassland, e.g. Trifolium repens (2. o.) Trifolium pratense (1. lo.) Poa trivialis (1. lo.) (The numbers in the list refer to the constancy groups of the species referred to.) 44 THF. CHANGING FLORA OF BRITAIN Table II. Environment of the Eutrophic Molinietum. Altitude Community — 500-1100 ft. O.D. E. latifolium — 900-1000 ft. Rainfall 60-70" per annum Soil permanently wet, deep peat (depth at least V 6") pH — 5 to 6.5 The following are analytical data for two sites in which E. lati¬ folium occurs. Valley A. 0-8" Dark peaty material Valley B. 0-6" Dark peaty material 6" + Light Brown peaty pH Exch. CaO % Available P205 % Exch. K20% 6.20 0.8 0.0291 0.255 5.28 1.72 0.0045 0.235 5.41 1.28 0.0059 0.320 REFERENCES. East, G., 1935, An Historical Geography of Europe. Gradman, R., 1931, Sild-Deutschland. Grimes, W. F., 1945, Early Man and the Soils of Anglesey, Antiquity, 19, 165-175. Hughes, R. E., 1940, Environment and settlement in the commote of Arllechwedd Isaf, Trans. Caernarvonshire Hist. Soc., 2, 1-26. - , 1949a, The Vegetation of the North Western Conway Valley, N. Wales, Part I. Environmental Factors (Climatic and Edaphic), J. Ecology, 37 , 306-334. - -, 1949b, The classification of grassland plant communities and its relation to that of the soil. Mutton, a. F., 1938, Place names and the history of settlement in South-West Germany, Geography, 23, 113-119. The following sources have been used in determining the pattern of human settlement in the Conway Valley. 1. Ministers’ Accounts for Wales in the Public Record Office for the 13th and 14th century. 2. The Record of Caernarvon 1352. 3. The Account of Bartholomeiv of Bolde. Bangor MS. 1939 (Circa 1400). 4. Jones-Pierce T. The Gafael in Bangor Manuscript 1939, Trans. Hon. Soc. Cymrodorion, 1942, 158-188. 5. Various Manuscripts in the Baron Hill and Vaynol Papers, housed at the University College of N. Wales, Bangor. The former papers cover a period from the late 14th century to the present-day. A detailed statement of the material used will appear in a later paper in the Journal of Ecology. DISTRIBUTION OF ER10PHORUM LATIFOLIUM 45 Key to Aerial Photographs (Published by kind permission of the Air Ministry). Pre-mediaeval occupation P M Mediaeval limits of land occupation Mediaeval sites of habitation O Sixteenth century limits of land enclosure Sixteenth century sites of habitation a Post-sixteenth century “squatter” enclosures • • • and sites of habitation Nineteenth century enclosures are indicated as 19 C The sites of Eriophomm latifolium E 4(3 THE. CHANGING FLORA OF BRITAIN SOME RECENT MODIFICATIONS IN THE FLORA AND THE VEGETATION OF THE VALOIS Paul Jo vet (Paris). (The following paper was delivered by Dr. Paul Jovet of the Museum National d’Histoire Naturelle, Paris, in French. It was so clearly enunciated that most of those present had no difficulty in following the theme, but it is thought preferable to publish this translation kindly prepared by Mrs. A. N. Gibby. The scientific names are those in cur¬ rent use in France and in some cases differ from those familiar in this country. — Editor.) The flora and vegetation of the Valois country, situated to the north and north-east of Paris, have been the subject of a recent publication.1 When comparing the daily observations made by the Abbe Questier between the years 1843 and 1876 with those made by other botanists, as well as myself (from 1924 to 1949), one notes the disappearance of certain species, the substitution of one species for another, new introductions and the creation of new stations. An attempt will be made to deal briefly with several of these modifications. Disappearance : — Lycopodium Selago was destroyed in a landslide immediately after its discovery. Rare Hepatics have disappeared as a result of the quarrying of siliceous sandstone. The tapping of springs has destroyed stations for Alneta- Sphagneta and Zannichellia. The clearing of the surroundings of ponds has eradicated Littorella uni flora and Limosella aquatica and Botrychium Lunaria, already rather rare during the last cen¬ tury, has not been found again. Fires on calcareous slopes have eliminated Bunium Bulbocastanum and certain orchids. Walkers and campers are responsible for the diminution of Phleum aren- arium and Pulsatilla vulgaris and the disappearance of Her- minium monorchis. Through the scraping of a wall Cystopteris fragilis has never re-appeared. Houses have been built over woods of Quercus lanuginosa (Q. pubescens) with associated Thalictrum minus, Inula hirta and Gentiana cruciata. Collectors have exterminated Ranunculus Questieri and Antennaria dioica. Substitutions: — Siliceous pastures, where Questier used to collect Myosurus minimus, Delia segetalis, Gypsophila muralis, etc., have been drained and their character altered by the appli¬ cation of lime; now, plants are to be found which are either indifferent as to soil or slightly calcicole The cleaning of seeds has resulted in the very considerable reduction in the occurrence of ljovet, P., 1949. Le Valois— Phytosociolog ie et Phytogeographie. See review by J. E. Lousley in 1951, Watsonia, 2, 143-144. MODIFICATIONS IN THE Jf’LOKA AND THE VEGETATION OF THE VALOIS 47 Caucalis daucoides ( C . lappula) and Lolium temulentum. Man lias removed Daphne Mezereum, D. Laureola and Anemone Hepa- tica to transfer them to parks made in Querceta-Fraxineta. Forest paths, now too well cared for, have lost many species such as Equisetum sylvaticum, Alchemilla vulgaris, but Agrimonia odo- rata and J uncus tenuis have become very common. Silicicole oak assemblages have been replaced by woods of Pinus sylvestris and Abies alba, where Goody era repens and Monotropa hypophegea are not rare (Questier did not come across these). In cultivated fields Questier saw Veronica persica once only at the end of his life; this species has now spread everywhere. At present Amaranthus Bouchoni and Chenopodium striatum are replacing Amaranthus retrojlexus and Chenopodium album. Recently Galinsoga parviflora has invaded beetroot fields in the Aisne Departement. On podsolic soil (with Erica tetralix ), which has already been greatly altered by the digging of peat holes, poplars are to be planted. Foresters greatly change many Alneta- Sphagneta, so that two species of Drosera have disappeared, as has Osmunda regalis from most of such localities ; they accelerate the normal process of evolution by planting trees in clearings and are responsible for the loss of Campanula persicifolia and Filipen- dula vulgaris (F. hexapetala). About 1860, Questier noted the first plantations of poplars; now all the valleys have become poplar forests; meadows where Schoenus nigricans, J uncus obtusiflorus (J. subnodulosus) and Gentiana pneumonanthe and Liparis Loeselii used to be found hardly exist now. The removal of peat has left large trenches filled with water which are being populated by Chara and the larger species of Hypnaceae. Thus evolution is starting afresh. Swertia perennis has become rather rare and Carex dioica and Senecio spathulifolius are no longer to be found. Volumes could be written concerning biotic factors, inter¬ competition among plants resulting in the extermination of Den- taria pinnata, fungal diseases, the activities of rabbits, deer, boars, birds, insects, etc. Creation of new habitats: — Questier saw about 1860 the first excavations for the railway lines ; embankments, strengthened by calcareous stones, have created very favourable stations for small bryophytes, especially Southbya nigrella, Cephaloziella Baum- gartneri, and so the extension of these has been greatly helped. Calcareous slopes in the open have been populated with Bromus erectus, Galium glaucum (Aspervla galioides), Lathy rus latifolius and Poterium muricatum, species unknown to Questier. In the neighbourhood of large sugar refineries, Chenopodium glaucum, C. ficifolium and C. rubrum have appeared. The banks of the rivers Oise and Ourcq have been reinforced in places by calcareous walls, and now mosses such as Cinclidotus riparius, C fontinaloides and Fissidens crassipes are plentiful, where they could not live formerly on the earthy banks. 48 THE. CHANGING FLORA OF BRITAIN Agropyron glaucum, now frequently found along the Oise, is not mentioned by Questier, nor the following plants which are to be seen along railway lines : — Erucastrum gallicum, Salvia verticillata , Eragrostis minor and the very common Senecio vis- cosus. He knew Linaria repens ( L . striata) in but one station; now it has been spread by the railway. Several secondary rail¬ way lines are now disused and some of these species will eventually disappear. On the sides of roads Euphorbia Esula is often seen and the great extension of Matricaria discoidea ( M . matricari- oides) came about after the 1914-18 War; now it is to be found on roads everywhere. Yet other species, unknown in the Valois in Questier’s time, notably Coronilla varia and many cultivated garden plants, have become naturalised, e.g. several species of Aster, Solidago Vir- gaurea and S. glabra, and, recently, Buddleja variabilis has greatly tended its range. In his parish of Thury-en- Valois Questier saw Prunus Padus planted in large numbers for the purpose of re-introducing trees on land occupied by heaths. Since then, P. Padus has been intro¬ duced into parks and gardens, but birds have caused its spread into numerous valleys. Similarly Alnus incana, planted in peaty valleys and also on certain calcareous slopes, has become fairly common, but its hybrid with A. glutinosa remains a scarce plant. If Acer Pseudo-plat anus is planted here and there in forests, it assumes the appearance of being spontaneous in the east of the Valois; it is often introduced in parks and gardens and along road verges; its seeds germinate very readily on waste ground, among ruins, wood-sides, etc., and everywhere it is naturalised with great ease. Thus we find here three woody mid-European species which are extending more and more from east to west. Conclusions : — During the past century many localities in the Valois have been greatly altered by the creation of meadow land, the bringing of land under cultivation (with the resulting disap¬ pearance of Lycopodium clavatum ), the building of houses, the construction of railways (and now the disuse of some of them), the quarrying of rocks, the excessive collecting of the rarest plants, numerous plantations of trees (poplars, coniferous trees, Ameri¬ can oaks, Robinia pseudo-acacia ), the maintenance of paths, drainage, etc. However, a fairly large number of localities noted by Questier have been re-discovered. Many new stations have been brought into being. If most of the plants introduced by man, voluntarily or otherwise, thrive in artificial stations, others have established themselves in habitats which are semi-natural or hardly altered; they really now form a part of the present flora of the Valois. RECENT ADDITIONS TO THE BRITI8H FLORA 49 RECENT ADDITIONS TO THE BRITISH FLORA (Exhibit) R. D. Meikle. Those who consider the British flora completely known and worked out will be surprised, I am sure, to learn that the list of post-war additions is so long that I have been compelled, for reasons of time and space, to limit my paper to but a fraction of the total. It has been difficult to know how and where to make the cuts, but two groups I almost immediately excluded — aliens and microspecies — the first because they are coming and going in an endless stream, occasionally leaving a mark on our landscape, as in the case of Senecio squalidus, but more often mere waifs and strays left to perish on a dunghill. Of the making of many micro¬ species there is, seemingly, no end, and I am afraid I find at times that much study of them, or many of them, is, as with books, a weariness of the flesh. If I were to include all the more recently dis¬ covered Hieracia, Orchids, Euphrasias, Rubi and the like, I am afraid my list would never end. Of the remaining groups, one has been excluded through want of personal knowledge — Potamogeton epihydrus, a very interesting addition to the American element of our flora, recently identified by Prof. Heslop-Harrison from material which he collected in the Outer Hebrides. Two Irish finds, Orchis cruenta and Orchis Traunsteineri, which I have exhibited, are plants for the specialist, and I am not competent to discuss them. Nasturtium microphyllum is by now sufficiently well known to you all to require no further discussion. Homogyne alpina, Agropyron Donianum and Milium scabrum are not really discoveries, but interesting re-discoveries confirming old records, not strictly within the scope of my exhibit. Patriotism moves me to add that three interesting plants, Hierochloe odorata, the Holy Grass, Cirsium heterophyllum, the Melancholy Thistle and Scheuchzeria palustris have recently been recorded for the first time from Ireland, but, compared with Eng¬ land, Scotland and Wales, Ireland is, for a great part, scarcely known botanically, and additions to the Irish flora are likely to be numerous as botanical investigation proceeds. Having dispensed briefly with the above, four plants, all Linneons, remain for more detailed consideration — two of them species new to the British Flora, two new genera and one also a new family — they are : Diapensia lapponica, first collected by Mr. C. F. Tebbutt near Fort William in Inverness-shire on July 5th 1951, and identified at Kew by Mr. R. A. Blakelock, who has since published a preliminary note on the discovery in the Kew Bulletin for 1951, page 325. Subsequent search has shown that Diapensia is relatively plentiful in the area where it was first found, and un- P 50 THE (HANGING FLORA OF BRITAIN doubtedly native there. It may yet be found elsewhere in W. Scotland, though it is strange that a plant, so conspicuous when in flower, should have escaped attention for so long, unless very rare and local. The Scottish plants have not yet been seen in flower, and it is hoped that further notes on the plant will be published when information is available. Diapensia lapponica (belonging to the family Diapensiaceae, new to the British Flora) has a circumarctic distribution, the var. lapponica (which includes the Scottish plant) occurring in Eastern N. America, Greenland, Iceland, Norway, Sweden, Finland, Russia and N. W. Siberia, the var. obovata in Western N. America, Kam¬ chatka, and N. E. Siberia. Diapensia was discovered, not by a botanist, but by an orni¬ thologist, in an area which many botanists considered “worked- out” or too dull to be worth a visit. The moral is obvious, and one can only hope that Mr. Tebbutt’s find will lead others to re¬ examine unpromising ground and give Clova and Lawers a rest. Koenigia islandica is one of the few British plants to have been first discovered in an herbarium. Specimens collected by Mr. H. M. Montford and Dr. Montford near the summit of the Storr on the Isle of Skye, on the 31st August 1934, and erroneously labelled Peplis, were found by Mr. B. L. Burtt in the Kew herbarium in 1950. Since that date Mr. J. E. Raven has re-found the plant in several localities and in considerable quantity in Skye, and sug¬ gests that Koenigia may be found elsewhere in Scotland. It is an inconspicuous herb, readily passed by as Montia or Peplis but quite distinct on closer examination, the nutlets are trigonous and typical of Polygonaceae. Koenigia, according to Mr. Raven, will grow in a variety of habitats, providing it is free from competition with more vigorous species. It is generally associated with plants such as Cherleria, Salix herbacea, J uncus triglumis, Sibbaldia, Arabis petraea and other common northern or montane species. Like Diapensia, it has a circumarctic distribution, occurring in both the Old and the New Worlds, but extends further south than Diapensia, to Tibet and Kashmir, and has been reported from Tierra del Fuego in southernmost America, though this record may refer to a closely allied species. Equisetum ramosissimum. A full account of this interesting discovery has been published by Mr. A. H. G. Alston in Wat sonia (1949). The Horsetail occurs along a limited stretch of river- bank near Boston, Lincolnshire, growing amongst long grass. It was first seen by Mr. H. K. Airy Shaw in July 1947. Although related to Equisetum hyemale and E. Moorei, Equi¬ setum ramosissimum differs from both of these in bearing a con¬ siderable number of lax, slender branches, and looks, at first sight, rather more like the hybrid Equisetum litorale, though the rough stems and apiculate cones show that it belongs to the subgenus Hippochaete. RECENT ADDITIONS TO THE BRITISH FLORA 51 Equisetum ramosissimum has a very wide distribution, scat¬ tered here and there throughout Eurasia, and in temperate and tropical Africa. In Europe it occurs chiefly in the Mediterranean area and in Southern Germany, but it has outposts in Brittany, Holland and the Rhine Valley, so that the British station is not altogether outside the range of its natural distribution. Horse¬ tails are rarely recorded as aliens, and it is most unlikely that Equisetum ramosissimum should have been deliberately planted at Boston. Perhaps, as with the Oak and Parsley Ferns in Ire¬ land, the Lincolnshire colony of Equisetum ramosissimum has developed recently from wind-borne spores carried westwards from the Continent. On the other hand, investigation may show that the plant is more widespread in the area than present records suggest. Cerastium brachypetalum was discovered by Mr. E. Milne- Redhead on May 18th 1947 on the bank of a railway cutting in Bedfordshire, between Sharnbrook and Irchester. All the British material collected has been referred to the variety eglandvlosum of Fenzl, which lacks the glandular hairs of the type. Cerastium brachypetalum is widespread in Europe, extending from Southern Scandinavia to the Mediterranean, and from Spain eastwards to the Caucasus. It is also recorded from North Africa, but is ap¬ parently absent from the North coast of France. The var. eglandulosum is essentially a plant of Central Europe, so that from habitat and knowledge of its extra- British distribution, it seems likely that Cerastium brachypetalum is a comparatively recent arrival. Further search may yet show that the Bedfordshire rail¬ way-side colony is, in fact, derived from native British stock growing in a natural habitat, for, to the uninitiated, Cerastium brachypetalum might easily be passed by as a form of the com¬ mon Cerastium viscosum , though the dense silvery indumentum of stems and leaves gives it a distinctive look. The species was included by Salmon in the lists of plants he considered likely to be found in Britain, and I am giving it special mention to-day in the hope that it may be discovered else¬ where. A good description of Cerastium brachypetalum and a key to the British Cerastia was published by Mr. Milne-Redhead in The Naturalist, 1947^ pp. 95, 96. Canon Raven remarked that during 1951 he had painted three new and important British plants from fresh material. Mr. Milne-Redhead said that since he had published his paper on Cerastium brachypetalum, his attention had been drawn to its occur¬ rence in Holland and Belgium and these countries should be added to the distribution given. LIBRARY UNIVERSITY OF WLm& 52 THE CHANGING FJvORA OE BRITAIN A ZOOLOGIST’S APPROACH TO A CHANGING FLORA Dr. Maurice Burton. The Royal Parks Committee on Bird Sanctuaries has repeat¬ edly expressed the opinion that where an undergrowth, particu¬ larly of bramble, is allowed to grow, small song-birds are encouraged to take up residence, and to nest, to a greater extent than where only thickets of rhododendrons are available. This is a sufficiently striking instance of the zoologists’ awareness of the effect on animal populations of a change in the flora. Again, the numbers of mistle thrushes have increased and the cause is believed to be the increased supply of food derived from the fruits of ornamental shrubs and trees. It is natural, in this heyday of ornithology, that our two first examples should be concerned with birds. Nevertheless, they illustrate the two main impacts on animals generally of changes in the flora : through the food-supply, and the provision or with¬ holding of shelter. A third example illustrates a further principle, the relative adaptability of animals. In the course of human settlement there is a radical reduction in the number of old and rotten trees. Woodpeckers nest in such trees; also they obtain their sustenance from the insect grubs assisting the dissolution of the wood. It has been suggested that, as a result of the reduction in number of suitably old trees, the green woodpecker may have become largely a ground feeder, digging for ants and possibly other things in the soil. Adaptability in the matter of food is expressed, however, in a natural catholicity in diet, so that the loss of one thing as the main article of food is counter-balanced by the adoption of an¬ other. The green woodpecker’s menu, for example, as taken from the Handbook of British Birds is: “chiefly larvae of wood¬ boring insects and ants ; cases of serious damage to bees and hives also recorded. In one case 50-60 millipedes foimd in one stomach ; remains of a bird’s egg also once occurred and worms eaten. Vegetable matter also eaten, acorns, pine-seeds, oats, Pyracantha berries, cherries and apples recorded”. The complete carnivore or herbivore is very rare. Among mammals the most striking exception is the koala, the Australian Teddy Bear, which takes nothing but eucalyptus leaves. More¬ over, leaves at the wrong stage of growth are said to be lethal. Such dependence upon a single food-plant is very rare. It still does not prove, however, that the koala is one hundred per cent, vegetarian. Whether it takes animal protein — say insects — in¬ cidentally, and whether such protein is essential to it is not known. A typical herbivore such as a cow probably takes in a A ZOOLOGIST'S APPROACH TO A CHANGING FLORA 53 fair amount of animal protein from invertebrates living on the grass; even the giant panda, with its main diet of bamboo shoots, is known to eat fish and small mammals in its wild state. On the other hand, such a typical carnivore as a lion is known to seek out a particular bulb and eat it, and to take fruits fallen from a wild plum-tree In any survey of the effects of a changing flora, it is necessary to keep food chains in mind. The lower invertebrates need detain us hardly at all, for apart from the Protozoa, whose linkage with the flora is somewhat obscure, the invertebrates on the land are mainly earthworms, dependent upon vegetation after it is broken down, and the mollusca, that seem capable of eating anything — living or dead vegetation, each other, the label of a matchbox, paper, and so on. In other words, both are supremely indepen¬ dent of changes in the flora. Even the mollusca, such as the Clausilias we normally associate with beech woods, seem to be able quite readily to transfer to another environment if the need arise. In insects, we have, however, another situation. First of all, their study is important because they are so numerous. Their species, probably number more than a million throughout the world, so that they represent a high percentage — probably three- quarters — of the animal kingdom. In populations they are as countless as the sands of the sea-shore. They afford the main and direct subsistence for many fishes (e.g. mayfly, caddis and so on), all our frogs, toads and lizards, many species of birds and not a few of our mammals, especially when bats are taken into account. Indirectly, by nourishing these, which are eaten by other animals higher in the food chains, insects can be said to sup¬ port the many birds of prey and of predatory mammals. If we count also the berry and fruit feeders among birds and mammals, insects acting as pollinators form a factor by no means negligible. If anywhere in our native fauna we should expect to find animals narrowly linked with a food plant, and therefore occupy¬ ing a precarious position in relation to potential changes in the flora, it is among insects. The very names of many of them suggest this. Examination shows, however, that to a large ex¬ tent even this is delusory. We speak of the privet hawk moth, and imagine that its sole food is the foliage of privet. Yet its larvae will feed equally well on lilac, laurustinus, guelder rose, holly and ash, and to a lesser extent on willow, dogwood, hop, snowberry, rowan, wayfaring tree, evergreen oak, forsythia and others. The larva of the cabbage white butterfly, despite its name, will feed on a great variety of Cruciferae. It is true that others are more restricted. The poplar hawk moth, so far as is known, takes only poplar and Salix. The pine hawk moth is restricted to Scots pine and Norway spruce. The convolvulus hawk moth lives on either the lesser or the greater bindweed. Many species seem to live exclusively on oak, others exclusively 54 THE CHANGING FLORA OF BRITAIN on birch or beech. On the other hand, it has frequently been found that captive larvae will take foliage of species other than those eaten in a wild state, and it must remain an open question, whether the linkage with a particular food plant is as close as is sometimes supposed. Another possible line of enquiry to be correlated with changes in the flora relates to the fact that some insects prey on a differ¬ ent food plant at different stages, even of the larval life. And it could happen that the mere upsetting of a plant association — removing an essential plant link — might be disastrous to a par¬ ticular species of insect even though the remaining species of plants were unaffected. But food is not the only, or even the major consideration. Two other factors must be considered. The first is shelter, and the second is the innate behaviour at pupation. A caterpillar used to feeding and pupating inside a bullrush may be quite well able to feed on another plant whose stems are not sufficiently great in dia¬ meter to give it shelter. But this question of shelter leads to an even more important aspect of our survey. The caterpillars of the wainscot moths have a very elaborate behaviour pattern. They bore through the stem of the rush and, after having made an entry plug the hole with detritus. One of them travels up the interior of the stem and, having ascended a certain distance, turns about so that it is head downwards. Then, just before pupating, it spins a web of silk across the lumen of the rush, the purpose of which is to keep the pupa from slipping down. There is, however, yet another link. Before ascending, the larva prepares the exit for the moth-to-come. Just below its own point of entry into the rush it eats away the wall of the stem outwards as far as the cuticle, leaving as it were a circular exit covered with a tympanum. When the moth emerges from the pupal case, it has only to brush aside the silken web, crawl down the stem and rupture the tympanum, to make its entry upon the world. It is axiomatic that, in a chain of instinctive behaviour, each succeeding action is touched off by the performance of the one preceding it. If for any reason an one action of the chain cannot be carried out the whole sequence breaks down. An example of the deep-rooted nature of instinctive behaviour is seen in the Cynthia moth, which pupates on a leaf, the caterpillar spinning a silken cocoon and drawing the leaf around the cocoon. To prevent the deciduous leaf falling, the silk of the cocoon is carried along the petiole and round the stalk. A Cynthia caterpillar placed in a box just before pupation will spin a cocoon of silk and will carry the silk along an imaginary petiole and round an imaginary stem. To return to the wainscot moth, if compelled to feed on some¬ thing other than the bullrush, probably everything would be all right until the time for pupation drew near. Presumably, then, the absence of any one of the many normal factors can serve to deflect the working out of the instinctive chain. The lumen of the plant stem may be too large or too small, the wall of the stem too A zoologist’s APPROACH TO a (HANGING FLORA 55 thin or too thick and so on. In a highly specialised species there is no margin for adjustment and presumably the chain would break down. Insects, then, are likely to suffer from one or other of the follow¬ ing if a change occurs in the flora: (1) from inability to change to a new food-plant; (2) from purely mechanical causes, such as in¬ adequate shelter; (3) from upsets in the chain of instinctive be¬ haviour at pupation; (4) and from an ecological conservatism. It is convenient to use the terms eury plastic and stenoplastic, to describe organisms that are tolerant of a wide variety of en¬ vironment and those tied to a narrow environment. In consider¬ ing these, much more than food and shelter, or even chains of in¬ stinct, are involved. Relative humidity will depend upon vegeta¬ tion and particularly upon forest growths, so will the amount of illumination, the temperature and so on. The spread of agriculture encourages certain species of insects at the expense of others, and such changes are most evident in the great increase in their populations. As a result, insectivorous birds increase in the culti¬ vated areas. But then, other factors come in to confuse the pic¬ ture. At the same time as these things are happening raptorial birds decrease, partly through persecution and partly through the destruction of trees, and with them their nesting sites. Then again, so long as hedges are cultivated the passerine birds are en¬ couraged. When they are cut down, shelter is lost and the pas¬ serines suffer. With the spread of agriculture the oaks are reduced in numbers, and jays that are so largely acorn-eaters suffer, or they turn to robbing nests or killing small birds. The use of artificial fertilizers, and especially the cult of the clean stable, reduces manure heaps and the litter and untidiness of the old-time farm¬ stead goes, and with it the insects associated with animal ordure. These are mainly dipterous flies and with their loss comes a diminution in swifts, swallows and martins. The interests of the farmer demands — or so it is usually thought — the destruction of the carnivorous mammals, stoats, weasels, martens, badgers, foxes, and, in turn, the rabbit, rat and mouse enjoy a heyday. All such changes are, however, of greater or lesser degree accord¬ ing to whether the species is euryplastic, like the rat, or steno¬ plastic, like the jay. There is yet another heading under which changes in a flora might conceivably affect a fauna, perhaps even catastrophically: through the trace-element. On this we have no more than scat¬ tered evidence, and the following discussion must be regarded as highly speculative. The cyclic plagues of lemmings as well as of voles, mice, rats, Arctic hares, and grey squirrels, and with them the inevitable increases in the numbers of their predators, have attracted a good deal of attention but there has been virtually no analysis of them, of the numbers involved or of their causes. In the first stage there is a vast increase of population, building up over a period of years. Then come the mass migrations, and, in the lemmings, 56 THE CHANGING FLORA OF BRITAIN the columns of teeming millions fanning out on a broad front, marching on and on until they finally commit suicide in the sea in their hundreds of thousands. Apparently the gemsbuck, be¬ fore man thinned its ranks, was given to a similar behaviour, also ending in a mass suicide in the waters of the South Atlantic, and every now and then one comes across a similar story for an¬ other species, usually a small mammal. Usually the story is of a column of animals having been seen, say of water shrews, which are normally fairly solitary. There can be little doubt that all these, well-known or fragmentary, stories belong to a related plexus of behaviour. So far the only explanation advanced is based upon investiga¬ tions carried out in recent years on the lemmings. If the results obtained are correct then we must believe that these pheno¬ menal increases in population, the mass migrations and fantastic suicides are the result of eating a particular lichen. The story does not end there, however. Apparently the lichen contains a vitamin which affects the anterior lobe of the pituitary, and through it the reproductive organs, giving a tremendous fertility. This becomes cumulative over the years. Moreover, it seems to impart a fearlessness, which accounts for the fact that the timid lemming marches in column with no thought of individual safety. The sequel seems to be even more extraordinary. The pre¬ dators, the owls, hawks, foxes and so on, after gorging themselves on “vitamin-drunk” lemmings become almost as fearless as they. The lemming story does not differ fundamentally from that of the oyster, whose spat cannot survive in water containing copper in less than one part in 700 million. It is believed, though not proven, that certain species of diatom provide this in the oyster beds, and that oyster beds without these diatoms are likely to be barren. It is not known why the common frog emerges from hiber¬ nation simultaneously over a wide area for the breeding assem¬ blies. Weather conditions do not appear to offer an explanation : the time may vary from the end of January to the beginning of March. Nor is it known why, on occasions, the frogs may assem¬ ble at the pond, yet not begin to breed for several days. It is suspected that the smell from the algae necessary for feeding the tadpoles is the trigger which brings the frogs into breeding con¬ dition. It is known that lions dig up a certain bulb and eat it; that the intensely carnivorous polar bear sometimes fills its paunch with vegetation; that most carnivores take some vegetable mat¬ ter at some time or another. But nobody knows why, and no¬ body seems to have tried intensively to find out. Major Anthony Buxton has studied the roe rings, has collected all the plants in these rings and finds that the one species common to roe rings is ergot. He suspects that eating ergot is a stimulant to breeding. His suggestion has not met a ready acceptance. a zoologist’s approach to a changing flora 57 Yet, against all these things we have a counter-mystery. The cycle of reproduction has been traced from the secretion of a hormone by the anterior lobe of the pituitary. It has been com¬ pletely studied except for one thing: What stimulates the pitui¬ tary to secrete the hormone? Is it the result of an internal rhythm, inexplicable and beyond our comprehension, or is it the result of a trigger action from something in the diet, a lichen, ergot, a bulb, an alga, a paunchful of greenstuff or some such thing ? There may be nothing in all these things but coincidence. Or it may be that vegetable protein only is necessary. It may be that a small group of plants of widely differing taxonomic rela¬ tions is involved ; or it may be, in perhaps the minority of cases, that a single species is involved. These things we do not know, for apart from Major Buxton, nobody seems to have investigated a single case in sufficient detail to give an answer. Most birds have a uro-pygial gland at the base of the tail (the so-called parson’s nose). Its function has long been a mystery, and probably is still, but it appears to depend on a trace- element. Fabricius found that nestling tufted duck fed on Daphnia were healthy and could swim. When the diet was changed to crushed fish, hard-boiled eggs and bread-and-milk, they became unhealthy and their feathers waterlogged when placed on water. They were sufficiently unhealthy that three out of five died in a few days. When the survivors were fed on water snails and swan mussels, they regained their health but the plumage was still not waterproof, until they were fed on grasshoppers. A similar thing was found for other species of ducks, and there is the clear indication that the Arthropod (crustacean or Insect) protein is needed to keep the preen-gland of ducks functioning. But what is the ultimate source of the essential materials? Pre¬ sumably it is vegetable in origin and presumably common to a number of species of plants. It is not impossible, however, that a given species of duck could depend for the essential material for its preen-oil, through its insect food, on a single species of plant and if that were removed suddenly (“a Zostera- incident”) the duck could die out. The paper was discussed as follows : — Dr. Butcher said that he was very interested in Dr. Burton’s re¬ marks about the possibility that the smell from algae provided the “ trigger ” which brings frogs into breeding condition. Algae have characteristic odours which are sufficiently marked for the human sense of smell to be able to distinguish between those of certain species. He was impressed by the ability of animals sometimes to distinguish be¬ tween plants — for example the only grass which his dog would eat is Agropyron repens. 58 THE CHANGING FLORA OF BRITAIN Dr. Heslop-Harrison suggested that in connection with Dr. Bur¬ ton’s comments on the olfactory sensitivity of frogs and Dr. Butcher’s on the odour of algae, it is interesting to recall some recent American work on the river specificity of fish. As is well known, Salmon will return to the river in which they were born to spawn, even after long intervals at sea, and when there are a large number of possible rivers to choose from. It has now been shown experimentally that fish can detect and remember subtle combinations of river “ odours in the water, and that these odours are organic in nature. They are actually volatile organic products, almost certainly arising from the algae grow¬ ing in the higher reaches of the river, each river having its own special combination. Prof. Tutin stated that when Zoster a marina was abundant in parts of our coast it supported characteristic animals. When it diminished in 1930 certain molluscs and a hydroid associated with it disappeared from the neighbourhood of Plymouth. Dr. Burton, in reply, said that this was an example showing that the dying out of a plant species entailed reduction and hardship for animal species rather than their extinction. The hydroid Lucinaria which was associated with Zostera marina was now found on other food plants. Prof. Osborn said that when he was at Adelaide he was responsible with Wood-Jones for the introduction of the koala from French Island into part of Kangaroo Island. It was now thoroughly estab¬ lished there feeding on the shoots of Eucalyptus. There might perhaps be some species in common between the two islands, but the general assemblage of Eucalypts was somewhat different. Dr. Burton’s re¬ marks reminded him of another Australian example of the relationship between an animal and plants. He was with Bateson in the Adelaide Hills in 1913 when Bateson caught a wanderer butterfly. The larvae of this insect are believed to feed only on asclepiads and these were then unknown in the locality. Subsequently one introduced species was found. Dr. Gordon Haskell said he would like to add another example to those mentioned by Dr. Burton. Maize is indigenous to some parts of the United States. Sweet corn is a sugary form of maize sometimes grown in England, and this is sometimes violently attacked by frit fly ( Oscinella frit). Out of 80 different strains examined he had not found one completely resistant to the insect, yet the English strains of the fly, which normally attack oats, have never before had the opportunity of being selected for their ability to attack maize. This is especially interesting as frit flies in America, which are regarded as morphologic¬ ally similar to the English strains, do not attack maize there. Some experiments were made by growing sweet corn and oats together in the expectation that the frit fly would attack oats in preference to the maize. But the maize still suffered, and was perhaps even preferred. Thus it appears that we cannot predict what changes in our cultivated plants may do to the food habits of our fauna. This may, in turn, have repercussions on the natural flora. BRITISH VEGETATION IN FULL-GLACIAL ANI) LATE-GLACIAL PERIODS 59 BRITISH VEGETATION IN THE FULL-GLACIAL AND THE LATE-GLACIAL PERIODS H. Godwin, The penetrating and extensive studies of the Late-glacial period made throughout Western Europe in the last two decades have been richly supplemented by those of Jessen (1949) and Mitchell (1951) in Ireland, and by others somewhat less frequent in Great Britain. In consequence of these investigations, there can remain no doubt that the Allerod climatic oscillation at the close of the last Glacial period has been adequately identified over a large part of the British Isles and this carries with it the recog¬ nition of the immediately preceding and succeeding cold periods, which as Zones I and III of the pollen analysis zonation make up, with Zone II of the Allerod period itself, the ‘Late-glacial’ in its present restricted usage. Exactitude is given to this termino¬ logy by the fact that the Allerod has been clearly identified as the Gotiglacial stage of ice retreat from Southern Scandinavia, and Zone III (equivalent to the Upper Dryas clay) as the stage of formation of the Norwegian Raa, the middle Swedish moraines and the Finnish Salpausselka. In Ireland we have the Athdown Mountain Glaciation in Zone III separated by the mild Aller0d stage from the latest stage of the Midland General Glaciation of that country. This degree of assurance makes it desirable, and helps to make feasible, the separate recognition of deposits of the last glacial period itself as distinct from those of the Late-glacial above de¬ fined on the one side, and those of the last Interglacial on the other. From Denmark we have excellent evidence of the char¬ acter of the last, the Eemian, interglacial of which it suffices to say that it clearly represents a period of some thousands of years’ duration, during which there was a full climatic cycle from arctic tundra, through coniferous and birch forest stages to the decidu¬ ous forest phase of a climatic maximum, and back by coniferous forest again to arctic tundra. It was a long period characterised at its height by warmth-requiring species of plants and animals, and impossible, in well- developed form, of confusion with de¬ posits of the glacial period which followed it. In the British Isles it has been recognised in a few places, and at one (Histon Road, Cambridge) a moderately long segment of the interglacial has been subjected to pollen-analysis (Holling worth, Allison & God¬ win, 1950). Between the deposits of this interglacial and those of the Late- glacial period sensu strict o must come in point of time those of 60 THE CHANGING FLORA OF BRITAIN the last glacial period itself. One need hardly stress the signifi¬ cance of the recognition of such deposits, which we may term “Full-glacial”, for an understanding of the nature of climatic and bio tie conditions in the last glacial period, and for assessment of the possibilities of survival or extinction of biota through that time. There are two series of British deposits which have, in my view, very strong claim to be regarded as ‘Full-glacial’, the so- called ‘Arctic Bed’1 described from many sites in the Lea Valley, north of London, at the ‘Ponders End’ stage of the evolution of the valley (Warren, 1912, 1916, 1923; Reid, 1949), and the ‘Arctic Bed’ of Barnwell Station, Cambridge (not to be confused with the older Barnwell Abbey beds) (Chandler, 1921). The evidence upon which this assignment rests is threefold : geological, faunis- tic and floristic. Zeuner (1945) has already made a tentative correlation of the Lea Valley Arctic Beds with stages of the last glaciation, a cor¬ relation essentially based upon the levels and gradients of the Lea Valley and those of the later stages of the Thames valley. He accepts the view that the last Glacial period is represented by three cold phases and two interstadials, as indicated for instance by the Flaming or Warthe, the Brandenburg and the Pomeranian moraines of the Scandinavian glacial area. In the first cold period (Wiirm I or LG1) he places the erosion of the Hedge Lane Channel, and this was filled in during the following interstadial in consequence of the restoration of sea-level which built the ‘Lower Flood-plain Terrace’. In the second cold period (Wiirm II or LG2) came the cutting of the Ponders End channel to a gradient distinctly below that of the Hedge Lane channel, and this was filled in during the second interstadial (LG2/LG3). Finally, during the third cold period (Wiirm III or LG3) he sug¬ gests there was the cutting by the Thames of the Tilbury chan¬ nel which has been filled in during the Post-glacial period. With¬ out necessarily accepting this detailed correlation, we can take it as showing that the geological evidence points clearly to a Full- Glacial age for the Arctic Beds of the Lea Valley. When Zeuner made this correlation the Nazeing channel stage of the Lea Valley had not been described (Allison, Godwin & Warren, 1952), but there is no doubt that it agrees in level and in age with the Tilbury channel. Pollen-analyses through its infilling of peat and calcareous muds show uninterrupted progress of deposition from Zone III at the close of the Late-glacial period through to the deciduous forest stage of the Post-glacial. The base of the chan¬ nel contains some slightly older material, partly fluviatile and partly lacustrine, which may be Late-glacial or may represent the last cold period of the Full-glacial. The dating of the channel filling not only establishes the age of cutting of the Nazeing chan- iThe ‘Arctic Bed* of the Lea Valley has hitherto been written of as a ‘Late- Glacial’ deposit, but this does not conform with the more exact modern usage of that term, and ought, I suggest, to be abandoned. BRITISH VEGETATION IN FULL-GLACIAL AND LATE-GLACIAL PERIODS GL nel itself as within the last glaciation, but places the deeper-lying ‘Arctic Beds’ with certainty into the Full-glacial. Pollen-analysis of the ‘Arctic Beds’ themselves has not so far proved practicable, but an attempt at radio-carbon assay kindly made by Libby (Godwin, 1951) has given a result of >20,000 years, a value amply sufficient to place it earlier than the Late-glacial (s.s.), the date of which (the Aller0d period) has been independently determined by the same method for various sites in the British Isles and the continental mainland. Now that Iversen in Denmark, and Jessen and Mitchell in Ireland have assessed the animal life of the Late-glacial period, it has become clear that the ‘Park-tundra’ of these areas supported a fauna characteristically rich in large herbivorous mammals such as horse, elk, reindeer, bison and giant Irish deer. Although the mammoth (Elephas primigenius) has once been found in the Late- glacial, this animal and the woolly rhinoceros ( Rhinoceros anti- quitatis ) are more characteristic of the Full-glacial and certainly lived in Western Europe during the last glaciation. These re¬ mains are quite typical and abundant in the Lea Valley Arctic Bed, where to be sure, they are accompanied by frequent bones of horse, some reindeer and probably by bison. The smaller mammals afford a less certain basis for distinguishing between the Arctic Bed and the Late-glacial of the Lea Valley, but the mollusca, abundant in deposits of both periods, are of value for this purpose. Kennard (Warren, 1912) distinguished the rich Lea Valley Arctic Bed as¬ semblage from those of all other Pleistocene deposits and sug¬ gested that they indicated a July isotherm of 8° to 10 °C for the period of their origin. He distinguished two groups of mollusca, the one containing truly boreal species, such as Sphyradium colu¬ mella , Vertigo parcedentata, Planorbis arcticus and Jaminia mus- corum var. lundstroemi, and the other consisting of dwarfed in¬ dividuals of species having a wider distribution. The Late- glacial molluscan assemblage of the Nazeing Channel lacks repre¬ sentatives of the former (boreal) group but represents a “modified survival of the stunted fauna of the Arctic Plant Bed” and Mr. Warren (Allison, Godwin & Warren, 1952) points out also certain further notable modifications. We shall later see that the floristic evidence bears out the strong probability that the ‘Arctic Bed’ deposits belong to a period distinctly different from, severer than, and older than those of the Late-glacial s.s., and may thus most reasonably be referred to the ‘Full-glacial’. It has so long been customary to consider tne Arctic Bed of the Barnwell Station pit at Cambridge as of the same age as the Ponders End Arctic Bed that we need not reiterate the arguments on which this is based: we fully accept the view that it must be regarded as Full-glacial also. The correlation table given in fig. 1 expresses some of the main features of presumed correlation between the British or West European deposits with which we are concerned. It will be noted 62 THE CHANGING FLORA OF BRITAIN S . S cojiduicWLX Corru moa <£ro und. Irdoaid, [stages Grc&t Britain AND SITES] FINI GLACIAL PERIOD AGE POLLEN ZONES PERIOD numerous situ Very numerous sites Post oLjidsl 8,000 Vil ATLANTIC is 1 1 _ ‘ BOREAL ‘ IV 'PRE -BOREAL' MIDDLE SWEDISH MO HAINES ^IaoaL 111 YOUNGER DRY AS VALLEY GLACIATIONS PERTH READVANCE QOTI CLAC/AL II ALLER.(j>D BaUxjbtta^li Kda^uui etc. Wkitrif HocJJiam WincLemere Star Carr NetuJuun Gancadden, Hawklor NazsJnx} etc BALTIC END-MORAINE DAN/ QLAC/AL hLfUVU >+.000 ? 1 OLDER DRYAS ? BILLING asuttatun, ? SCOTTISH 1 t READVANCE POMERANIAN END MORAINE ' ? BRANDEN BURG END MORAINE Fait oUxiAl i VJE ICHSL CLA l :l Cl AT ION _ MIDLAND GENERAL GLACIATION NEW ^ ponders), end Lea, Valley Antic Bed BamWell Station, • C DRIFT Fig. 1. that the Late-glacial can be approximately dated as between 10,000 and 15,000 years of age, vastly shorter than the Full- glacial which preceded it. The correlation with continental stages, especially for the Full-glacial, is meant only as tentative and general. We have not elaborated the correlation or sub-division of the Post-glacial period, the stage of climatically improved conditions including the Post-glacial climatic optimum and extending to the present day. Throughout the lowlands of the British Isles it has been a period of woodland dominance, of birch and locally of pine in the earliest stage (Zone IV) but afterwards of pine and of the mixed-oak-forest components with Corylus and Alnus, later still with the addition of Fagus and Carpinus in southern England. The task of correlating the Full-glacial and Late-glacial stages with the direct field evidence for the position of the British ice of the last glaciation is as yet barely begun. It seems likely that Zone III, the cold spell closing the Late-glacial was represented BRITISH VEGETATION IN FUEL-GLACIAL AND LATE-GLACIAL PERIODS 63 by valley glaciations of small magnitude in the Scottish highlands, the Lake District and Wales. Zone I has been taken to correspond with the Scottish Re-advance (represented by the Boulder clays extending south from the Southern Scottish Uplands over the western Lake District and parts of the Isle of Man). Support is given to this view by the certain recognition of the Allered deposits within the area of the Scottish Re-advance at Whitrig Bog in Berwickshire, and at Garscadden Mains near Glas¬ gow (Mitchell, 1952). The equivalent of the Scottish Re-advance in Ireland is not yet certain, but may be the Athdown Mountain Glaciation in Wicklow. Far outside the limits of the Scottish Re-advance lies the boundary of the ‘New Drift’, extending from Filey in N.E. Yorkshire across the Vale of York, and diagonally across England to South Wales, and crossing Ireland from just north of Wexford to the estuary of the Shannon. We must suppose that the Full -glacial deposits formed in the period of the New Drift, in the milder stage between that and the Scot¬ tish Re-advance, and possibly within still undetected stakes of advance to, or oscillation within the New Drift. It will be recognised that, even were the Lea Valley and Barn¬ well Arctic beds formed at the period of greatest extension of the New Drift, the glacial margin of that time would, nevertheless, have been at least 100 miles (160 km.) to the northwest, and if they formed during a recession (as seems more likely) then the dis¬ tance may have been considerably greater. In either event, they appear to be sufficiently related to the maximum extension of the last ice sheet for their floras to be taken as characteristic of British plant life during the severest or almost the severest part of the last glacial period. Members of the fossil floras of the period may be taken in general to be either perglacial survivors or species which, if incapable of persistence in the most exacting stages of the glaciation, nevertheless were present by immediate colonisa¬ tion after amelioration. There are two ways of investigating the flora of the Late-glacial and Full-glacial deposits; for the Late-glacial beds, both pollen- analysis and identification of macroscopic plant remains have been practised; for the Full-glacial deposits, the latter method only. Whilst the strength of pollen-analysis lies in the general picture which it is able to convey of the vegetational picture and so of climatic and biotic conditions, that of the identification of macro¬ scopic remains lies in the much greater security of specific recogni¬ tion and the greater likelihood that the plants actually grew close to where their remains have been found. It goes without saying that there is a very great advantage in combining the two largely complementary methods. Pollen analyses from deposits of Late-glacial age have shewn that, taken as a whole, it had vegetation of the character of ‘Park- tundra’. The high ratio of non-arboreal to arboreal pollen be- 04 THE CHANGING FLORA OF BRITAIN speaks an open landscape with scattered clumps of birch trees, although closed birch woodlands (with pine in Holstein) charac¬ terised the milder Allerod period itself. Sedges and grasses con¬ tributed very largely to the herbaceous pollen, but along with these many other types occur with high constancy, and often with high frequency, for example Armenia, Artemisia, Campanula, Centaurea, Epilobium, Filipendula Ulmaria, Galium, Helianthemum, Plan- tago media, Polemonium coeruleum, Ranunculus, Rumex, Sangui - sorba officinalis, Succisa pratensis, Thalictrum, Valeriana officin¬ alis, Selaginella selaginoides, Botrychium, Lycopodium, and Ophioglossum. Pollen of Caryophyllaceae and Chenopodiaceae, of Labiatae, Umbelliferae and several types of Compositae occurs abundantly and confirms the general picture of a rich herbaceous vegetation. Less abundant but equally informative pollen records are those for Centaurea cyanus, Linum, Scleranthus and Pastinaca sativa. Empetrum nigrum pollen is often abundant, especially in the more Atlantic regions as Jessen has pointed out for N.W. Ireland during Zone II. The abundant birch pollen comes partly from Betula pubescens, partly from B. nana, and the willow pollen partly from Salix herbacea (which in Ireland strongly characterises Zones I and III) and partly from other species such as S. phylid- folia. Jessen and Mitchell have identified much macroscopic plant material of Late-glacial age from Ireland, Mitchell and Miss A. P. Conolly have made several records from two Scottish sites, and several workers have contributed to the records for various sites in different parts of England. Possibly the most prolific of these have been Hawks Tor in Cornwall and Nazeing in the Lea Valley, both sites of special interest lying far south and distant from the edges of the dying ice sheet. From these sources it has been possible to put together a floristic fist for the Late-glacial of the British Isles to set alongside the very full and careful records for the early Full-glacial worked out for Barnwell and the Lea Valley Arctic Bed. The following lists are based for convenience upon the phytogeographic cate¬ gories devised by Matthews (1937), but they include also species no longer native here. The species which Matthews placed in his category of wide European and extra-European range have not been dealt with. The question mark in the lists indicates a merely tentative identification and the bracketed records for Scotland are from old sites taken to belong to the Late-glacial upon somewhat doubtful evidence. It will be appreciated that with so much active research in progress these lists are out of date almost from the moment that they are made, and during even the last month [March 1952] Mr. Frank Mitchell has made many notable additions to the Irish list. BRITISH VEGETATION IN EULLr-GLACIAL AND LATE-GLACIAL PERIODS 65 TABLE 1. BRITISH FULL-GLACIAL and LATE-GLACIAL PLANTS. A. Arctic- Alpine “Historical Northern” (Matthews). Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. v ? • • Arabis petraea ... Arctostaphylo8 uva-ursi Betula nana Carex incurva (maritima) C. atrofusca (ustulata) C. capillaris Draba incana Dry as octopetala Empetrum nigrum Polygonum viviparum ... Salix lapponum S. reticulata Thalictrum alpinum + 4- + 4- + 4- + 4- + 4- 4- + 4- + 4- 4- 4- + + + 4- (+) 1 4- + + 4- 4- + 4- + + 4- 4- 4- 4- + 4- 4- 4- 4- + B. Arctic-Alpine “Historical Tertiary”. Arenaria ciliata agg. Carex atrata C. lagopina Cerastium alpinum Eriophorum angustifolium Loiseleuria procumbens . . . Oxyria digyna Potentilla Crantzii Salix arbuscula Saxifraga oppositifolia ... Vaccinium uliginosum ... Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. 4-4- + 4- + + + 4- + 1 1 • • ? ( +) + + + ( + ) + + 4- + + + C. Species no longer Native. 1. Montane, arctic and alpine. Arenaria biflora ... (Betula nana in Ireland) Papaver alpinum Potentilla nivalis P. nivea . Pedicularis hirsuta Ranunculus aconitifolius R. hyperboreus R. nemorosus Salix polaris . Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. 4- 4- 4* + 4- 4- 4- 4- • 4- 4* + + ( + ) fi 0(3 THL CHANGING FLORA OF BRITAIN Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. lr. 2. Totally extinct. Silene coelata Reid ... ... 4- + Linum praecursor Reid ... 4- 4- 3. Continental. Gentiana cruciata ... ... 4- D. Alpine. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Arenaria aedoides ... ... 4- Saxifraga hypnoides ...... + + E. Arctic Subarctic. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Cornua suecica ... ... ... ? Primula scotica ... ... ... 4- F. Northern Montane. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Arenaria gothica • • • + Polemonium coeruleum • • • + + Potentilla jruticosa 4* + + Primula farinosa ? • Rubus saxatilis ... • • • + + Salix phylicifolia + + Subularia aquatica • • • + 4- G. Continental Northern. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir Andromeda polijolia • • • + + ( + ) Betula pubescens • • • + + 4- 4- Carex disticha • • • + + C. pulicaris • • • + + + Cicuta virosa + 4* Cirsium heterophyllum + ? • ? • Comarum palustre • • • + + 4- 4- 4- Eleocharis midticaidis . . . + 4- Littorella lacustris ? • + ~f“ 4- Viscaria alpina ... + Menyanthes trifoliata ... ... + + + 4- 4- 4- Potamogeton fill] or mis ... + + + 4- 4- 4- P. obtusifolius + + + 4* 4* P. praelongus • • • + + 4" ? 4- Potentilla procumbens ... ? • • • • Salix aurita • • • ? • Sparganium angustifolium • • • + 4- Vida sylvatica ... • • • + Viola palustris ... 4- + 4- 4- 4- BRITISH VEGETATION IN FULL-GLACIAL AND LATE-GLACIAL PERIODS 67 H. Continental. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Holo8teum umbellatum ... + + Potentilla argentea ... + Ranunculus Lingua . . . •+* 4" -t + I. Continental Southern. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Oenanthe Lachenalii ? • • • • (+) J. Oceanic Northern. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Cochlearia danica ... *+- C. officinalis ... + + Naias flexilis ... + + Silene maritima ... ... + K. Oceanic West European. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ir. Carum segetum ... ... -f + E. tetralix ... + -t Myriophyllum alterniflorum ... ? + + + + Damasonium Alisma L. Oceanic Southern. Late Glacial. Barnwell. Lea V. Late Gl. Eng. Scot. Ip. 4- • • • • • • i M. Mediterranean. Not represented. A, B. Arctic-alpine. Taking the Full-glacial and Late-glacial records together, they include one-third of the present British Arctic-alpine element, 26 out of a total of 76, the Full-glacial contributing a somewhat larger proportion than the Late-glacial to this number. Some species occur both in the Full- and in the Late-glacial lists, but whilst chance must be largely responsible for this, it is note¬ worthy that the two Arctic willows, Salix arbuscula and S. lap- ponum, have not yet been found in Late-glacial beds. It seems highly probable that plants in this category survived the last glaciation in Britain. Their Late-glacial distribution areas were in many instances very much wider than their present ranges, a fact illustrated by the distribution maps for Betula nana, Thalictrum alpinum, and Salix herbacea. This restriction of rangr must be considered due to the conditions of the Post-glacis period, whether caused directly by climatic change or indirectly through the operation of other causes. 68 THE CHANGING FLORA OF BRITAIN C. Extinct plants. Two plants now no longer known living have been recorded from the Full-glacial deposits. One, Silene coelata Reid, rests upon evidence which makes it certain that it was a distinct species, the other, Linum praecursor Reid, is open to some doubt since it seems closely similar to L. anglicum. However, Miss J. Allison has found specimens precisely matching L. praecursor in East Anglian interglacial material. Among species still living but not found in Britain, Gentiana cruciata has a continental distri¬ bution, but the rest are montane, arctic and alpine. If we except the dubious record of Salix polaris from the Scottish Lowlands, all the extinct species come from the Full-glacial deposits, but one naturally cannot say whether the extinction was attributable to Post-glacial or to earlier conditions. That extinction of Arctic-alpine plants has occurred in the Post-glacial period is shown by the case of Betula nana which has now been found in Ireland in the Late-glacial, although the plant is no longer living there. Doubtless many more remain to be added to this list. It is interesting to note that Papaver alpinum L., Arenaria biflora L., Potentilla nivalis Lapeyr., are high alpine plants, Gentiana cruciata is also alpine and their presence in the Full-glacial is in line with a relict explanation for the present dis¬ junct northern distribution of alpine species. Potentilla nivea agg. is arctic-alpine, and Ranunculus hyperboreus a high arctic species. Pedicularis hirsuta is an ‘Amphi- Atlantic’ arctic plant of limited occurrence in northern Scandinavia. It is not quite clear to what groups the identifications of Ranunculus aconiti- folius and R. nemorosus refer. D. Alpine. One of the nine species in Matthews’ Alpine element is re¬ corded in the Full-glacial and one in the Late-glacial. E. Arctic- Sub arctic. Of the 30 species placed by Matthews in the Arctic- Subarctic element, two (one doubtful) have been recorded from the Full- glacial, none from the Late-glacial. F. Northern montane. Of 25 species in the Northern Montane element, two (and one doubtful) have been recorded from the Full-glacial, and five from the Late- glacial. Among them there are further instances of restriction of range since the Late-glacial period. Particularly notable is the case of Polemonium coeruleum which has a very restricted and scattered range to-day: its complex and charac¬ teristic pollen grains have now been found in a number of Late- glacial deposits in various parts of England from Cornwall, Sur¬ rey, and Shropshire to Yorkshire, lying far outside its present area. Subularia aquatica with a pronouncedly northern range in Britain has been recorded from the Late-glacial in Cornwall, and BRITISH VEGETATION IN FULL-GLACIAL AND LATE-GLACIAL PERIODS 69 Potentilla fruticosa with a notably restricted and disjunct distri¬ bution to-day occurred in both the Full- and Late-glacial outside its present range. G. Continental Northern. Matthews has placed 91 British species in his Continental Northern Group ; ten (plus two tentative recognitions) have been recorded for the Full-glacial, and fifteen (again plus two tenta¬ tive recognitions) from the Late-glacial. As might be expected, a number of these records lie to the south of the present range of the species concerned. H. Continental. Of the 82 species placed in Matthews’ Continental element one occurred in the Full-glacial, one in the Late-glacial, and Ranun¬ culus lingua was found in both. The most remarkable of these records is that made by Mr. P. A. Tallantire of Holosteum umbel- latum from the Late-glacial of East Anglia. I to M. Other geographic groups. The Continental Southern element, in which Matthews has placed 127 British species, has only a single dubious record from the Late-glacial, but the Oceanic Northern, containing 19 species, has two records from the Full-glacial, and two from the Late- glacial. Naias flexilis, however, is certainly more characteristic of the early Post-glacial than of the Late-glacial, and is often very abundant in Irish lake deposits of the younger period. The present restriction of range of this species must then certainly be regarded as a Post-glacial phenomenon The Oceanic West European element, which contains 76 species, has one tentative record only for the Full-glacial, whilst in the Late-glacial there are three. Myriophyllum alterniflorum has been doubtfully re¬ corded from the Full-glacial, but its pollen has been seen in Late- glacial deposits in England, Scotland and Ireland, and has indeed long been recognised as characterising deposits older than the Boreal period. The one record of Damasonium Alisma from the Full-glacial in the Lea Valley alone represents the 74 present species of the Oceanic Southern group: although the identifica¬ tion is beyond question and the fragile nature of the carpels seems to preclude the possibility that it has been secondarily in¬ corporated in the ‘Arctic Bed’ at Hedge Lane its presence then appears anomalous. Unfortunately, the stratigraphic situation at this site was complex and never properly resolved. The Mediter¬ ranean group, in which Matthews places 38 species, has no re¬ presentatives in the Full- and Late-glacial records. The percent¬ age Late- and Full-glacial representation of the present British flora in the different geographical groups is given in Table 2. The Arctic-alpine is most strongly represented; but the Northern Montane, Alpine, Continental Northern, and Oceanic Northern are almost as abundant. As we have pointed out, in the extinct 70 THE CHANGING FLORA OF BRITAIN species and Arctic-alpines the Full-glacial has the heavier repre¬ sentation, but in the Continental Northern and Northern Montane the preponderance is in the Late-glacial records. TABLE 2. BRITISH FULL GLACIAL AND LATE GLACIAL PLANTS. Analysis of Species Identified in Matthews's Groups. % of present Group size. Full Glacial. Barnwell. Lea V. L.G. Total. Br. flora in the category 38 Mediterranean 0 0 0 0 0 127 Continental Southern 0 0 ? ? ?1 74 Oceanic Southern 0 1 0 1 1 76 Oceanic W.-European 0 ? • 3 3 5 82 Continental 2 0 2 3 4 19 Oceanic Northern 1 1 2 4 21 91 Continental Northern 4? 9? 15?? 19 21 25 Northern Montane 1 1? 5 7 28 76 Arctic Alpine 14 11 13? 26 34 9 Alpine 1 0 1 2 22 30 Arctic Subarctic 1 • 0 2 7 — Montane- Alpine non¬ native 5 5? ? 10 — Extinct 2 2 0 2 — ( ? signifies a dubious identification) A further difference which emerges from comparison of the full records is that, apart from Juniperus (and pollen possibly derived or wind-carried from a distance), trees are unrepresented in the Full-glacial lists, whereas the Late-glacial records include Betula pubescens (the most abundant tree), B. pendula, their hybrids with Betula nana, Sorbus (most probably S. aucuparia), and Populus tremula. It is as yet uncertain whether Pinus was present, for macroscopic records are lacking and pollen, although often quite abundant, is insecure as an index of immediate pre¬ sence. It would appear from these comparisons that although the Full- and the Late-glacial records shew considerable similarity in floristic composition there is a definite indication of greater clima¬ tic severity in the Full-glacial, as already the molluscan and glacio- logical evidence have shewn. Certain other features emerge from a consideration of the records from a slightly different angle : when grouped ecologically rather than phytogeographically it becomes apparent that two categories bulk particularly large in the lists both of the Full- glacial and of the Late-glacial. The first of these is roughly de¬ fined as “Aquatic or Marsh plants,” their prevalence no doubt in part due to the preference given to such species by the condi¬ tions of preservation, and partly to the wide geographical and BRITISH VEGETATION IN FULL-GLACIAL AND LATE-GLACIAL PEKIODS 71 climatic range of plants in this category. Their abundance is reflected both in pollen and in seed records. The second group is that of ruderals or weeds, and here the very long list must indicate the prevalence of open conditions, bare soil surfaces and freedom from competition. It will be noted that Polunin has strongly emphasised that plants of his category of ‘Arctic’ species demand these conditions also. These identifica¬ tions make it evident that many weed species hitherto thought to be introductions to Britain by Neolithic and later agricultural¬ ists are of much older standing. We may note especially Linaria vulgaris, Galeopsis Tetrahit, Polygonum aviculare, Sonchus arvensis, Taraxacum officinale, Stellaria media, Cerastium vul- gatum, Ranunculus acris, and R. repens and the abundant pollen of Rumex, Artemisia, and other Compositae. Mr. Tallantire has found a single grain of Centaurea Cyanus (a species already known from the Danish Late-glacial) and we may recall the pollen identi¬ fications also of Plantago media and Pastinaca sativa. It may well be said that there is nothing here which disproves the sug¬ gestion that they may have been subsequently extinguished and later reintroduced, but in several instances repeated discoveries at all stages of the Post-glacial render such an hypothesis un¬ necessary. These positively dated records bear out in striking manner the opinion expressed by Salisbury as long ago as 1932 when he wrote of ‘the considerable area of morainic deposits that must have fringed the European ice front throughout the pleistocene glacia¬ tions’, that “It is not improbable that this was the primary home of species which to-day are mainly, if not exclusively, associated with the artificial conditions of cultivated and disturbed soil”. It is apparent that these species, suppressed and restricted by the closed forests which covered the lowlands, and the peat mires which covered much of the uplands, survived the greater part of the Post-glacial period on cliffs, beaches, river-banks and screes until the destruction of the native forest by prehistoric man gave them opportunity to expand once more. That such species can have a place in the British Flora irrespective of human introduc¬ tion is clearly shewn by the numerous ruderals and weeds repre¬ sented in the river channel deposits of the Clacton Interglacial, for although man was present then his numbers and influence were doubtless small. As a final comment upon the lists of identified species from Full-glacial and Late-glacial deposits it may be noted that species characteristic of the undergrowth of deciduous woodlands are totally or almost totally absent, and that the presence of such species as Calluna vulgaris, Erica Tetralix, Petroselinum segetum and Empetrum nigrum , the latter abundant, reinforces Jessen’s view that the Late-glacial climate of the British Isles must have had a definitely Atlantic character then as now. These species have not been found in the Full-glacial. 72 THE CHANGING FLORA OF BRITAIN To conclude, the evidence shews the Full-glacial landscape in Britain to have been a tree-less tundra and that of the late-glacial to have been treeless or lightly wooded ‘Park-Tundra’. In both, there was a herbaceous flora rich in species especially of the categories of ruder als and weeds, aquatic and marsh plants: the chief phytogeographical caegories present were Arctic-alpine, Northern Montane, Continental- and Oceanic- Northern, and Alpine, but there were present also large numbers of plants of wide general distribution. The flora in Late-glacial time had some oceanic tendency. At this time open habitats and fresh soils abounded, and dispersal was easy for species without exacting warmth requirements; since the North Sea basin was dry during Full- and Late-glacial time, spread from the Continent was also easy. The evidence shews that many plants were widespread at this time which now have a restricted and disjunct areal distribu¬ tion. In the Post-glacial period the spread of forest, coupled with progressive leaching of soils and the spread of mires in forest- free areas, has greatly restricted the range of all species requiring open habitats. Where dispersal had been easy and rapid for them, it now became slow or ceased. In short, we cannot doubt that these Post-glacial events have been responsible for some, and perhaps many, of the so-called ‘relict’ distribution ranges hitherto explained as due to survival “in situ” through the last glaciation. Although the Full-glacial records go far towards shewing us the nature of perglacial survivors in this country, the significance of this is lessened by the realisation that their present ranges have been determined not so much by the localities of such survival, but by later events. The realisation that phases of rapid and general dispersal may alternate with phases of fixity, adds much to our resources in interpreting contemporary distribution phenomena, especially when it is understood that phases favourable for the spread of one category of plants may be unfavourable for others. The analysis we have attempted has been restricted to data from the Full- and Late-glacial periods, but similar information is available and becoming more abundant for Interglacial and Post¬ glacial deposits also. The extension of the records for identified plant remains from all these periods, dated precisely by pollen- analysis or other techniques, and visualised against a clear picture of the events of the Pleistocene period, will clearly afford the in¬ formation we are entitled to regard as a factual basis for phyto- geographic theory. REFERENCES. Allison, J., Godwin, H., and Warren, S. H., 1059, Late-glacial deposits at Nazeing in the Lea Valley, North London, Phil. Tr. Roy. Soc., B., 632 , 236, 169. Chandler, M. E. J., 1921, The Arctic flora of the Cara Valley, Quart. J. Geol. Soc., 78. 4 BRITISH VEGETATION IN FULL-GLACIAL AND LATE-GLACIAL PERIODS 73 Godwin, H., 1949, The spreading of the British Flora considered in relation to conditions of the Late-glacial period, J. Ecol., 37, 140. - , 1951, Comments on Radiocarbon dating for samples from the British Isles, Am. J. Science, 249 , 301. Holling worth, S. E., Allison, J., and Godwin, H., 1950, Interglacial deposits from the Histon Road, Cambridge, Quart. J. Geol. Soc., 105 , 495. jessen, K., 1949, Studies in Late Quaternary deposits and flora history of Ireland, Proc. R. Irish Acad., B., 44, 205. Matthews, J. R.. 1937, Geographical relationships of the British Flora, J. Ecol., 25, 1. Mitchell, G. F., 1951, Studies in Irish Quaternary deposits : No. 7, Proc. R. Irish Acad., B., 53, 111. Reid, E. M., 1949, The Late-Glacial flora of the Lea Valley, New Phytol., 48, 245. Salisbury, E. J., 1932, The East Anglian Flora, Trans. Norf. and Norivich Nat. Soc., 13, 191- Warren, S. H., et. al., 1912, A Late-Glacial stage in the Lea Valley, Quart. J. Geol. Soc., 68, 213. - , 1916, Further observations in the Late-Glacial stage of the Lea Valley, Quart. J. Geol. Soc., 71. 164. - , 1923, The Late-Glacial stage of the Lea Valley (Third Report), Quart. J. Geol. Soc., 79 , 603. Zeuner, F. E., 1945, The Pleistocene period : its climate, chronology, Jaunal suc¬ cession-, (Ray Society), London. This paper was discussed as follows : — Dr. Dahl asked if Dr. Godwin could state the total number of species now recorded from the Late-glacial. Dr. Godwin replied that it was of the order of 200. Mr. Milne-Redhead enquired whether the pollen of Diapensia lappo- nica, a circumpolar plant recently discovered in Scotland, had been recorded from any of the deposits mentioned in the paper. Dr. God¬ win, in reply, said that the pollen of this species was not easy to dis¬ tinguish and he would prefer to identify it from macroscopic remains. It had not yet been recorded. Dr. Baker said that all fossil remains of Armeria maritima examined in this country have been of the dimorphic subsp. maritima, which now extends from the north of the Iberian peninsula to southern Greenland. Therefore, it should not be classed as a member of an “ Arctic-alpine ” element, but rather as “ Oceanic Northern.” Dr. Godwin replied that there would have to be modifications of Matthews’ lists but broad gene¬ ralisations could be made on this basis. He agreed that there was no reason to suppose that any fossil material identified as Armeria mari¬ tima could not be included in the subspecies now found on our shores. Mrs. M. L. Davis asked if the pollen of Stachys alpina had been found. Dr. Godwin replied that it had not. He said that the pollen of Labiates was particularly difficult to identify and it must be remem¬ bered that it was usually not possible to identify species from pollen alone. Pollen was valuable for giving a general view of the vegeta¬ tion : for the identification of species it was generally necessary to have macroscopic remains. The two methods had to be used together. Dr. Godwin said that in making identifications it was necessary to consider the whole background of the European flora and especially those species which now occur in Scandinavia. 74 THE CHANGING FLORA OF BRITAIN Mr. Rose enquired whether the “ Full-glacial ” of Dr. Godwin’s paper referred to the maximum glaciation in Britain when the ice sheet reached the vicinity of London. Dr. Godwin replied that this maxi¬ mum glaciation was earlier than the one he had spoken of as the Full- glacial, and represented a much greater period back in time. Oanon Raven asked if the speaker could give any indication of how far the sites identified and examined could be regarded as representa¬ tive and complete. Dr. Godwin said that for every site examined there must be thousands waiting to be done. For example, it was known that in Shropshire alone there were a very large number of end moraines full of material waiting to be worked. Seeds and fruits of dry¬ land plants were only preserved in steep-sided basins and the deposits could never be regarded as completely representative of the flora of the time they were laid down. Prof. Webb asked if there were any fossil records of sycamore ( Acer Pseudo plat aims) in Britain. This species was unique in the British flora, as a well-established alien, thoroughly at home here, whose native territory was not far away. Why it is not now native is rather puzzling, and it would be especially interesting to know if it ever had been. Dr. Godwin replied that fossil material of the sycamore had not been identified. He agreed that it was somewhat remarkable that it did not appear in the Post-glacial until introduced by man. SOME LATE-GLACIAL PLANTS 75 SOME LATE-GLACIAL PLANTS (Exhibit) D. Walker and R. G. West. Dr. Godwin has already drawn attention to the differences between the ‘full glacial’ and ‘late-glacial’ floras recovered from peat and mud beds in Great Britain. It is with the strictly Late- glacial period and the Post-glacial period which followed it that this paper is primarily concerned. Many Late-glacial deposits are now known in the British Isles but for the purposes of illustrating our main points we have chosen to consider a pollen diagram from the fen bordering Skelsmergh Tam, a little north of Kendal in Westmorland at 400 ft. O.D. The work at this site has only recently been started and nothing more than a preliminary account is yet available. The lowest metre of mud contains abundant pollen of her¬ baceous plants along with Salix , Betula and Pinus pollen. This stratum certainly covers the Late-glacial period, and the diagram clearly illustrates the threefold division into two tundra phases separated by a period of more or less closed birch woodland. Most of the Betula pollen belongs to the tree birches (fruits of Betula pubescens have also been recovered from these muds) but some certainly belongs to B. nana , a determination which we have been able to make following the publication by Terasmae (1951) and the close examination of our own type material. It is signi¬ ficant that Betula nana pollen has never been recorded from the Skelsmergh deposits above the Late-glacial layers. We had tentatively referred some of the Salix pollen to S. herbacea (Straka, 1952) and this suggestion was rendered more plausible by the discovery of Salix herbacea leaves in the muds of the upper tundra zone. Although grasses and sedges contribute much of the herbace¬ ous pollen to the Late-glacial spectra, Artemisia, Rumex, Thalic- trum and Caryophyllaceae contribute very substantial amounts ; whilst Helianthemum, Plantago media, Galium, Empetrum, Fili- pendula Ulmaria, Chenopodiaceae and Compositae (additional to Artemisia) are consistently represented. Whilst all trace of these herbs virtually disappears for the greater part of the Post-glacial period, some of them recover with the advent of human agriculturalists, probably during the Neo¬ lithic and subsequent periods (cf. Godwin & Tallantire, 1951). The grasses and sedges react most strongly to the clearance of the forests but Artemisia and other Compositae, Rumex, Cheno¬ podiaceae and Umbelliferae also reappear in the pollen diagram at the same level and in considerable frequency. Some quite new 76 THE CHANGING FLORA OF BRITAIN pollen types are also recorded and are very probably the result of human introduction, Plantago lanceolata, P. major and cereals being the most abundant. These are all herbs which to-day are widely distributed over the British Isles wherever there are suitable fields or other clear spaces. Their occurrence in the Late-glacial is associated with the open habitats, often on unstable frost-moved soil, which seem to have been characteristic of the period in this region. Their distribution areas became dissected and restricted during the Post-glacial forest period, but there seems to have been no climatic barrier to their expansion when suitable habitats became available again (Godwin, 1949). A number of plants which we have come to recognise as typi¬ cal of the Late-glacial period in northern England did not return to the lowlands after forest clearance and still have notably disjunct highland, coastal or northern distributions in Great Britain although apparently widely distributed during the Late- glacial. Betula nana and Salix herbacea are the most obvious examples of such plants which also include, in the Skelsmergh records, Armeria maritima, Hippophae rhamnoides, Selaginella cf. selaginoides and Lycopodium clavatum. For some of these plants (e.g. Armeria maritima ) it may be that some undetected feature of inland lowland ecology limits their extension, but with plants such as Betula nana it appears that it is a climatic bar¬ rier, perhaps the maximum summer temperature (Dahl, 1952), which is active now but was not active during the Late-glacial period. It remains for future research in both ecology and palaeo- ecology to shed further light on these problems. As Quaternary Research develops it becomes increasingly apparent where some of our major ecological problems lie. We wish to thank Dr. H. Godwin, F.R.S., for his encourage¬ ment of this work and Mr. E. F. T. Elbome for taking the photo¬ micrographs for the exhibit. REFERENCES. Dahl, E., 1952, Personal communication. Godwin, H., 1949, J. Ecology, 37, 140-147. GODWIN, H., & TALLANTIRE, P. A., 1951, J. Ecology, 30 , 285-307. STRAKA, H., 1952, Svensk. Bot. Tidsk., 46 : 2, 204-227. Terasmae, J., 1951, Svensk Bot. Tidsk., 45:2. 858-361. DISTRIBUTION OF SOME ALPINE VASCULAR PLANTS 77 PRESENT DAY AND LATE-GLACIAL DISTRIBUTION OF SOME ALPINE VASCULAR PLANTS IN SCANDINAVIA AND THEIR INTERPRETATION (Exhibit) Eilif Dahl (Oslo). There are reasons to believe that many arctic-alpine plants are absent from the lowlands of Scandinavia not only because of competition but also because the climate is unsuitable to them. A number are of types which it is difficult to imagine would be exterminated by competition, and many are difficult to grow in gardens in absence of competition. Observations on the behaviour of these plants in gardens as well as nature point in the direction that high summer tempera¬ tures are detrimental to them, for in gardens they tend to suffer during the particularly warm periods. A confirmation of this hypothesis can be obtained by compar¬ ing the distribution of the alpines with the meteorological obser¬ vations. The maximum summer temperature was selected for study since the plants seem to suffer during the warmest periods. From all meteorological stations in Norway, Sweden, Denmark, and Finland the average yearly maximum summer temperature has been calculated. This in itself will not help us much because the stations usually are situated in the valleys while the alpines grow in the surrounding mountains. The maximum summer temperatures on the summits can, however, be calculated because the temperature decreases with altitude in a fairly regular man¬ ner, 0.6° C. per 100 m. altitude. In this way has been calculated the maximum summer temperature in a very large number of the highest points in the terrain all over Scandinavia. From these it is possible to draw isotherms, the isotherm of 24° C. (see fig. 2) separates an area with summits with a maximum summer tem¬ perature of 24° or lower from an area where no such cool summits exist. And these isotherms are now compared with the distribu¬ tion of the species. As the first example (fig. 2), the distribution of Poa flexuosa Sm. is compared with the 24° C. isotherm. As will be seen the isotherm and the distribution limit coincides very closely. The absence of the species from the warm areas around Trondheim is especially instructive. As the second example the distribution of Sedum Rosea (L.) Scop, is compared with the 25° C. isotherm, (fig. 3). On the south coast of Norway the species is confined to the immediate proximity of the sea with its cooling effect on the extreme summer temperature ; the same applies to some localities in Bohuslan. 78 THB CHANGING FLORA OF BRITAIN Fig. 2. The Scandinavian distribution of Foa ftexuosa Sm., according to Nannfeldt, with the 24* C. isotherm. DISTRIBUTION OF SOME ALPINE VASCULAR PLANTS 79 Pig. a. The Scandinavian distribution of Sedum Rosea (L.) Scop., according to Lid Zachau, with the 25* C. isotherm. The strength of these arguments depends upon a detailed correspondence between the distribution limits and the isotherms. A very detailed mapping is, therefore, essential and any filling out of areas, especially along the borders, will blur the picture. 80 THE CHANGING FLORA OF BRITAIN Fig. 4. The present day and subfossil occurrence of Salix herbacea L. in Fennoscandia, according to Hulten, with the 26* C. isotherm. Shaded : Areas where S. her - bacea is common. Dots : Outlying localities. Rings and crosses : Subfossil late- glacial finds. In the next example (fig. 4), the distribution of Salix herbacea L. is compared with the 26° C. isotherm. In some outlying localities the plants are washed down from the mountains by the rivers and form hardy permanent colonies. Also the occurrence of Salix herbacea in Late-glacial and Post-glacial beds outside its present range is entered. In South Scandinavia such finds are DISTRIBUTION OF SOME ALPINE VASCULAR PLANTS 81 confined to Denmark and the adjacent parts of Sweden. This is a character it shares with other species, e.g., Salix reticulata. While the regional distribution of Salix herbacea can be under¬ stood in terms of climate alone, this cannot be done in the case of Salix reticulata L., which is a calcicole species. Its absence from large areas of the South Scandinavian mountains (see fig. 5) is indubitably due to dominance of archaean rocks giving no suitable soil for the species. Allowing for this the distribution corres¬ ponds fairly well with the 26° C. isotherm. Fig. 5. The present clay and subfossil occurrence of Salix reticulata L. in Fenno- scandia, according to Hultfin, with the 26° C. isotherm. Shaded, Areas where S. reticulata is common. Dots : Outlying localities. Rings : Subfossil late- glacial finds. F 82 THE CHANGING FLORA OF BRITAIN Fig. 6. The present day and late-glacial occurrence of Dryas octopetala L. in Fenno- scandia, according to Hulten, with the 27° C. isotherm. Shaded : Areas where Dryas is common. Dots : Outlying localities. Rings : Subfossil late-glacial finds. DISTRIBUTION OF SOME ALPINE VASCULAR PLANTS 83 Dryas octopetala L. (see fig. 6) is a still more calcicole species than Salix reticulata , hence the restriction of range due to edaphic factors is still more marked. In some areas it has a wider dis¬ tribution than Salix herbacea and reticulata , it has a wide range in North Finland and goes down to the lower mountains and the sea in South-east Norway. The distribution corresponds fairly well with the 27 ° C. isotherm. In contradistinction to Salix herbacea and S. reticulata , sub¬ fossil Dryas has been found in numerous places north of Scania and also on the Baltic coast. Botanists have for some time been aware that finds of real arctic-alpine species in Late-glacial beds are restricted to southernmost Sweden and Denmark. Besides the two Salices, this applies to Diapensia lapponica, Silene acaulis , Saxifraga oppositijolia and Ranunculus hyperboreus. Farther north only Dryas, Betula nana and Arctostaphylos alpinus have been found, and north of the Middle Swedish Moraines (running from the outer Oslofjord across Sweden to Stockholm) Dryas is absent, the characteristic Late-glacial fossil being Hippophae. All the available facts are consistent with an hypothesis that the summer temperature rose to between 26 and 27 degrees centi¬ grade when the ice withdrew from the areas north of Scania. Such high summer temperatures must have been combined with a rapid retreat of the ice, and geologists have found a rate of re¬ treat of 100-150 m. per year when the ice withdrew north of Scania. North of the Middle Swedish Moraines the figure is still higher. Most geologists agree that the Middle Swedish Moraines cor¬ respond to the climatic deterioration during the Younger Dryas Period, corresponding to zone III in Britain. The rapid retreat of the ice north of Scania would then correspond to the Aller0d period (zone II in Britain). It is likely that species with delimit¬ ing isotherm substantially lower than 26° C. would have a very bad time and probably become extinct during this period. This is a point of importance in connection with the problem of the origin of the Scandinavian alpine flora. It is likely that similar patterns will be found by the study of British Late-glacial plants. The abundance of Salix herbacea in Late-glacial beds of Ireland, its presence in Cornwall and in north Great Britain but its apparent absence in south-east Eng¬ land may perhaps be explained in a similar way. But more in¬ vestigations are needed to substantiate this. I am indebted to the British Council for the opportunity to be present at this meeting. REFERENCES. Dahl, E., 1952, On the Relation between Summer Temperature and the Distribu¬ tion of Alpine Vascular Plants in the Lowlands of Fennoscandia, Oihos, 3, 1-31. 84 THE CHANGING FLORA OF BRITAIN GLACIAL RELICS IN THE NETHERLANDS Dr. Ch. H. Andreas (Groningen). The changing of a flora may mean two different things. In the first place it may mean a geographic, a visual change — just as we say that a landscape changes during a train journey, let us say from south to north. In the second place it may mean a historical change, the change of a landscape or a flora in the course of years, as to which we may consider the few years of a man’s lifetime as well as the geological periods of thousands and millions of years. In speaking about glacial relics of the Nether¬ lands, I shall restrict myself to the last mentioned historical changing of the flora. I need not go into details on the various shiftings of the ice- sheets in earlier periods, nor need I explain the term “glacial relics”, which in botany covers plants of an ordinary arctic, northern and perhaps alpine distribution, which, preceding the ice, came down from their ordinary area and which stayed in some of the new localities after the retreat of the ice. Those plants are characterized by a so-called disjunct area ; they are of a local occurrence and do not spread actively, though there may be some spreading in consequence of more recent changes of climatic and edaphic conditions. During the third of the four glacial periods, the so-called Riss- period, the northern half of the Netherlands was actually covered with ice, which had its southern borderline running from Amster¬ dam to Utrecht and further down to the south-east. We shall not deal with this period to-day, though the climate may have been not too bad and there may have existed some vegetation at that time. But also the Wurm-period, when the ice did not reach further than southern Sweden, had its indirect influence on the flora of the Netherlands; fossil remains of plants of a tundra-vegetation of that time have been found in the eastern part of the country, plants such as Salix herbacea, S. polaris, S. reticulata, Betula nana, Arctostaphylos Uva-ursi, Dry as octopetala and Selaginella. They went back to their northern stations along with the ice. Yet some plants are likely to have remained in their Dutch localities; we may instance Cornus suecica, Linnaea borealis, Trientalis europaea, perhaps Arctostaphylos Uva-ursi and Rubus saxatilis and perhaps Scheuchzeria palustris, Carex limosa and Eriophorum vaginatum of the eastern Sphagnum-bogs. Prob¬ ably there is one more species, Carex aquatilis, with which how¬ ever we shall deal later on. We usually consider these plants, especially Cornus, Linnaea and Trientalis, as glacial relics in the Netherlands; but there is a difference of opinion about their GLACIAL RELICS IN THF, NETHERLANDS 85 status as such between Dutch botanists in connection with the fact that our country lies in the route of migratory birds which migrate in autumn from Scandinavia and the Baltic to the south, such as species of the genera Corvus (crows) and Turdus (thrushes) for example (Fig. 7). Map of distribution iD the Netherlands of Comus suecica e , Linnaea borealis ■ Tritntalis europaea A, Car ex aquatilis -f (present localities) and x (fossil re¬ mains). The lines are three out of many, demonstrating routes of migration of the sr.ng thrush (Turdus e. ericetorvm). 86 THE CHANGING FLORA OF BRITAIN Comus suecica and Linnaea borealis grow locally on diluvial grounds in the northern provinces of the Netherlands, but their area is not clearly disjunct. Between the Scandinavian and the Dutch region there are known scattered localities in Denmark and in north-west Germany respectively, which lie on the route of those migratory birds which are berry eaters, in autumn at least. And as the fruits of both species are berries, the late Pro¬ fessor Weevers presumed a transport of the fruits by those birds and consequently a more or less recent settlement (or resettle¬ ment) of Comus and Linnaea in the Netherlands, where they sometimes occur in historically young vegetation. For this reason he proposes to call these plants pseudo-relics, not relics. The same may hold good for Arctostaphylos Uva-ursi, growing on the isle of Terschelling and in one place in the centre of the country. Trientalis was known from the east and north-east of the Netherlands and within the last 30 years it was also discovered on two of our North Sea islands, Terschelling and Vlieland. The theory of a transport of its capsules together with earth on the feet of birds at least to the Dutch isles is less attractive than that by the berry eating birds in the case of Comus, Linnaea and perhaps of Arctostaphylos. Yet the occurrence of Linnaea in a fairly young vegetation of pine- woods is not necessarily an objec¬ tion against its position as a glacial relic. For glacial relics need not have been constant as to their localities from glacial times up to the present, provided there were alwavs suitable growing conditions available. There will have been little migration from one place to another. Only the aid of an uninterrupted series of fossil remains will enable us to decide in favour of the relics. Betula nana in the German Erzgebirge gives a most striking example of such a series. We now turn to Car ex aquatilis , a plant which has been found in the Netherlands two or three times during the last hundred years. But the specimens had not been recognized as such for in the herbarium they had been erroneously named Carex acuta or Carex gracilis. They were recognized only recently by three Dutch field botanists who predicted its present occurrence in the north of our country. And, indeed, one year after their pre¬ diction, in May 1948, one of my colleagues and I rediscovered Carex aquatilis, growing in a pool in the same village where it had been found in 1 845 ; we do not know whether it was exactly the same locality. Afterwards we also found the plant in the province of Drente, while the Natural History Club of Groningen discovered a small but very abundant colony near to the above- mentioned station in 1951. Carex aquatilis most resembles Carex gracilis, from which it differs however by its blunt-edged stalk, its very long lowest bract which is considerably longer than the inflorescence, by the turn¬ ing upwards of it-s drying leaves (Carex gracilis turns downwards) GLACIAL RELICS IN THE NETHERLANDS 87 and by its pale green nerveless utricles. The base of the stem is purplish and the leaf-tips are bluish-grey. Now I consider Carex aquatilis as another glacial relic of the Netherlands. It is an arctic-subarctic plant of circumpolar dis¬ tribution. Its occurrence in the Netherlands means a disjunc¬ tion, for Carex aquatilis, has not yet been found in Germany or in Denmark, and there is a distance of about 700 kilometres between the Dutch and the Swedish stations. The distribution in Europe can be seen on the map. I am not certain about Iceland, where Dr. Love, who knows its flora well, denied the presence of Carex aquatilis , but its occurrence in Iceland is men¬ tioned in botanical literature. Yet this uncertainty cannot influence my opinion. The questions which remain are whether the plant grew in our country in the Pleistocene and, secondly, has it found suitable circumstances for its growth ever since? The first question can be answered in the affirmative. Fossil remains of Carex aquatilis were found in the east of our country (Hengelo) in the tundra-flora of the Wiirm-glacial period men¬ tioned before, together with such plants as Dryas octopetala and Salix reticulata. Moreover, it was found in a lock-chamber near Wijk bij Duurstede in a layer of clay of the Late-glacial period and it is remarkable that with it the fossil remains were found of plants which grow together with Carex aquatilis in its present habitats: — Betula, Salix, Alisma, Carex, Comarum, Eleocharis, Filipendula, Mentha, Menyanthes, Nymphaea, Oenanthe, Ranun¬ culus (Batrachium included), Sparganium. Moreover a very rich Late-glacial vegetation of Carex aqua¬ tilis was found in Germany, together with Betula nana. It will be difficult to trace whether Carex aquatilis has been able to stand climatic conditions, that is to say temporarily different combinations of many factors ever since the Pleistocene, but Betula nana in Germany is a proof that there is at least one plant able to do so. And why should not there be more? Palaeobotanical investigations in the Netherlands have shown already that stagnant water, probably the chief requisite for Carex aquatilis, has been present on boulder clay in the province of Drente ever since the end of the Pleistocene. And its present occurrence in old riverbeds points to the possibility of the tiding over in such places in certain climatic periods, such as the Atlantic with its decreasing number of open pools and a develop¬ ment of Sphagnum bogs which made the struggle for life more difficult for Carex aquatilis. As far as I know from a distribution map, kindly procured me by Mr. Nelmes of Kew Herbarium, Carex aquatilis occurs in Wales, northern England and Scotland. To my knowledge it has not yet been found in the famous Teesdale region. In Ire¬ land it grows together with Carex rigida, with which it may be 88 THE CHANGING FLORA OF BRITAIN confused in the fossil state. Yet the remains of Carex aquatilis do not seem to be the most difficult to be distinguished within the genus. I hope that palaeobotanists in my country will pay attention to the species and find an uninterrupted series of fossil remains from the Pleistocene up to the present time, by which they would strongly support my hypothesis that Carex aquatilis is a glacial relic in the Netherlands. I wish to express my thanks for the kind invitation from your Society, and for the aid of the British Council, which enabled me to attend your conference and join your excursion, and to con¬ tribute this communication. This paper was discussed as follows : — Dr. Walters said that Carex aquatilis Wahlb. was now known from Teesdale. He had recently seen it near Middleton. Mr. Meikle stated that a colony of Carex aquatilis grows by the side of the reservoir at Glenasmole, Bohernabreena, Co. Dublin. This is an artificial habitat, and the sedge is not known to occur as a native else¬ where in the vicinity. It has been flourishing at Glenasmole for many years, and its origin remains unexplained. BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS 89 SOME PARALLELS BETWEEN THE BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS (Exhibit) A. Melderis. A selection of specimens, as well as some maps showing their distribution, was exhibited to illustrate the close relationship between the British and Scandinavian mountain floras. As regards the geographical distribution, the mountain plants common to both floras can be divided into three general groups. The first group, which corresponds to the Arctic-subarctic element of Matthews (1937), contains about 37 exclusively northern species, not extending to the mountains of Central and S. Europe. Nearly half of them (about 16) belong to the boreo-atlantic species which are distributed in N. Britain and Scandinavia (in some instances also in Spitzbergen and Novaya Zemlya), reach¬ ing sometimes the Faeroes, Iceland, S.E. Greenland and eastern N. America. Several species have amphi-atlantic distribution, being confined to the two sides of the North Atlantic Ocean (cf. Hulten, 1950). Thus, Cerastium Edmondstonii (Edmondst.) Murb. & Ostf., Draba norvegica Gunn. ( D . rupestris R. Br.), Euphrasia frigida Pugsley*, Erigeron borealis (Vierh.) Simm., Festuca vivipara (L.) Sm., and Carex recta Boott extend to N. America. Poa flexuosa Sm. (not found in the Faeroes) reaches Greenland. Its hybrid with P. alpina f. vivipara L. (P. x jemtlandica (Almq.) Richt.) is found in Scandinavia, Scotland and Iceland. Alchemilla Wichurae (Bus.) Stefansson seems to have the same range as P. flexuosa, but it is met with also in the Faeroes. The plant recorded from a locality in Riesengebirge probably belongs to alpine A. connivens Bus. which is closely re¬ lated to A. Wichurae. Arenaria norvegica Gunn., formerly referred to A. ciliata L. (growing in the Pyrenees, Alps and Carpathians), reaches Iceland, but has not been found in the Faeroes as yet. (Fig. 8). Euphrasia scotica Wettst. extends to the Faeroes. The following species are so far recorded only from N. Britain and Scandinavia: Hieracium reticulatum Lindeb., H. stictophyllum Dahlst. and H. argenteum Fr., Carex Grahami Boott and Orchis purpurella T. & T. A. Steph. * Callen '1952) has regarded E. frigida and E. eurycarpa Pugsley as varieties of E. arctica Lge. ( E . Marshallii Pugsley), the first as var. obtusata (E. Joerg.) Callen and the second as var. submollis (E. Joerg.) Callen (distributed in Nor¬ way, Scotland, Iceland, Greenland and Canada). The British species of Euphrasia are in need of further critical revision. 90 THE CHANGING FLORA OF BRITAIN Fig. 8. The distribution of Arenaria norvegica Gunn. (•), A. gothica Fr. MB), A. ciliata ssp. htbernica Ostf. & Dahl (A) and of A. cilia ta ssp. pseudofrigida Ostf. & Dahl iO). The other species of the first group (about 21) are widespread in the arctic, subarctic and montane regions of the northern hemi¬ sphere and most of them have a circumpolar distribution, e.g., Koenigia islandica L. (found in the Isle of Skye), Sagina inter¬ media Fenzl, Minuartia rubella (Wahlenb.) Hiern, Saxijraga rivu- laris L ., S. caespitosa L. (Fig. 9), Diapensia lapponica L. (recorded from Glenfinnan in Inverness), Poa pratensis ssp. alpigena (Fr.) Hiit., Poa glauca Vahl, Eriophorum brachyantherum Trautv. [E. opacum (Bjornstr.) Fern.], Carex saxatilis L., C. rariflora (Wahlenb.) Sm. and Luzula arcuata Sw. BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS 91 The second group, which includes the Arctic-alpine element of Matthews, comprises more than 80 species, the general range of which lies in the arctic or subarctic regions and reappears farther south in the mountains of Central and S. Europe. The majority of them, e.g., Salix reticulata L., Viscaria alpina (L.) Don, Dryas octopetala L., Potentilla Crantzii (Cr.) G. Beck, Loiseleuria pro- cumbens (L.) Desv. and Gyiaphalium supinum L., occur also in the mountains of Asia and/or America. Some species of this group have also amphi-atlantic distribution, similar to that of the first group. Thus, e.g., the range of Alchemilla alpina L. and Veronica fruticans Jacq. extends to Greenland, but that of Salix herbacea L., Cerastium alpinum L., Saxifraga stellaris L., Alchemilla glomerulans Bus. and A. filicaulis Bus. reaches eastern N. America. Fig. 9. The distribution of Saxifraga caespitosa L., after Ldve & Lore (1951). 92 THE CHANGING FLORA OF BRITAIN Judging from the climatic and soil requirements these groups include species having a suboceanic, sub- or low-arctic range (cf. Bocher, 1951). The typical high-arctic plants growing in con¬ tinental climatic conditions do not occur in the British Isles, but they are represented in the N. Scandinavian mountains where they have occupied situations corresponding to continental tundra. Some of them, termed west-arctic, such as Arenaria ciliata ssp. pseudofrigida Ostf. & Dahl (Fig. 8), A. humifusa (Wahlenb.), Stellaria crassipes Hulten, Potentilla Chamissonis Hulten, Poa arctica var. caespitans (Simm.) Nannf. and Carex holostoma Drej., have also an amphi-atlantic distribution, but in contrast to the above-mentioned species they occur in higher latitudes. In addition, the Asiatic element enriches still more the Scandinavian mountain flora. The third group of the species common to the British and Scandinavian mountain floras is represented by the ubiquitous element, occurring both in the lowlands and highlands, e.g. Trol- lius europaeus L., Anthyllis Vulneraria L., V actinium Myrtillus L., Campanula rotundifolia L., Solidago Virgaurea L. and Festuca ovina L. In many cases these species have developed peculiar montane biotypes. The distribution of the plants belonging to the first two groups gives a valuable indication of the age and origin of the floras in question. Their geographical areas are discontinuous. It is very difficult to explain the occurrence of these species in their present situations separated by the broad seas and oceans, especially with regard to the Faeroes, Iceland and Greenland, if we accept the view of older authors, e.g. Nathorst (1891) and Ostenfeld (1901). Ac¬ cording to them, the vegetation of the countries in question, as well as in northern Europe, had been destroyed by a great ice- sheet during the Ice Age. The arctophilous species could have survived at the margin of the glaciers. These authors assumed that present vegetation could have arrived there at the end of the Ice Age after the retreat of the glaciers, travelling from more southern or eastern regions over a big land bridge. Modern students of the arctic flora, as well as the geologists, nevertheless deny the presence of such land connexion in the post-glacial period. If the connexion existed, the disappearance of it must have taken place much earlier. In that case the plants could have arrived in the isolated countries only by the aid of birds, air, sea-currents and man, but we have no evidence at present that these means could have played an important role in the dis¬ persal of the montane species. Thus, according to A. & D. Love (1951, p. 394), of all (about 585) higher plants in Iceland, “not more than 30 per cent have been introduced in historical times, not more than 15 per cent might have dispersed by aid of mainly sea-currents in post-glacial and pre-historical times . . .”. At the end of the last century Blytt (1893) showed that the “extinction” theory cannot explain the occurrence of some N. American and Greenland plants in Scandinavia. The absence of lilUTlSH AND SCANDINAVIAN MOUNTAIN FLORAS 93 them on the European continent and in Siberia excluded their immigration from the south and east. Blytt considered them as relicts of an interglacial flora, which had survived one or more glaciations there. Later he assumed that these western plants had immigrated to Scandinavia before the last glacial period over a transatlantic bridge connecting Greenland, Iceland, the Faeroes, Scotland and W. Norway. His ideas of the survival of the plants in Scandinavia during the Ice Age, supported also by Sernander (1896) and Hansen (1904), were substantiated by Th. E. Fries (1913) in a detailed “over- wintering” theory, which was based on a distribution of the mountain species (in all 140) in Scandin¬ avia and in other countries, as well as on some geological facts. Since the publication of this theory extensive research work has been done by Scandinavian botanists, dealing with the distribu¬ tion, taxonomy and cytology of the mountain plants. In many cases, it has been proved that Scandinavian plants, which for¬ merly were identified with species occurring on the mountains of Central Europe, differ from them, e.g. Arenaria norvegica, Euphrasia lapponica Th. Fr. and Poa flexuosa. These discoveries give a valuable indication in favour of the survival of the plants in Scandinavia (cf. Nordhagen, 1935; Nannfeldt, 1935, 1947; Selander, 1950, etc.). The studies of the distribution of the mountain plants in Scan¬ dinavia revealed also that they occupy two separate areas. One of these areas is situated in the mountains of S. Norway, where several endemic forms, such as Papaver relictum (Lundstr.) Nordh., Draba cacuminum E. Ekm., Poa arctica var. stricta (Lin- deb.) Nannf., etc., have been recorded. Also the majority of the boreo-atlantic species common to the Scandinavian and British floras occur there. As they could immigrate neither from the south nor the east, it has been assured that they may have survived in some ice-free refuges, when the Ice Age was at its maximum. From the distribution of these plants, it has been possible to determine somewhat accurately the locations of the refuges, which seem to be localised on or near the sea-shores (in Vaage- Lom-Lesja District and in Dovre). The other area is confined to the northern part of Scandinavia (from Salten to W. Fin mark and Tometrask District in Swedish Lapland). It is occupied also by many interesting plants, such as west-arctic species and several endemic forms, e.g. Papaver Laestadianum Nordh., P. lapponicum (Tolm.) Nordh., Taraxacum tornense Th. Fr., Poa arctica var. tromsensis Nannf. and var. microglumis Nannf. These species together with others may have found some refuges in the same area, near the sea-shore and on some “nunataks”. Several Scan¬ dinavian plants, e.g. Saxifraga hieraciifolia Waldst. & Kit., Rhodo¬ dendron lapponicum (L.) Wahlenb., Campanula uniflora L., Corex arctogena H. Sm. and Luzula parviflora (Ehrh.) Desv., have “bicentric” distribution, being distributed in both areas. The discontinuity of the range of these plants is explained gener¬ ally as a result of the survival of them in two different parts of THE CHANGING FLORA OF BRITAIN 9 4 Scandinavia. Bocher has assumed that this discontinuity may have been caused by climatic and edaphic conditions. M. Fries (1949) has expressed an opinion that numerous arctic- alpine as well as many subalpine plants have survived in different refuges, scattered along the sea coast. From the sheltered stations the survivors could spread inland after the melting of the ice. Now they occupy those situations on the mountains where the environmental conditions are most suitable for them (cf. Bocher). It can be accepted that not only herbaceous plants could have survived in refuges, but also trees and shrubs. According to Nannfeldt (1947), Betula callosa Noto (found also in Iceland) and other mountain birches, willows, Myricaria germanica (L.) Desv., etc., may be glacial survivors. In western Jamtland the remains of Hippophae rhamnoides L. have been found in the deposits of the late glacial period, and Nannfeldt assumes that it could have survived in a refuge in Norway. This plant in southern Sweden seems, however, to be an immigrant in the early post¬ glacial epoch. When the floras of the other boreal regions were more com¬ pletely studied, a number of rare species as well as endemic forms were found in or near the situations which later have been recog¬ nized by geologists as never having been glaciated. Thus, Fer- nald (1925) showed that numerous species in boreal N. America (in St. Lawrence region) have survived the Ice Age. Warming (1888, 1891), Gelting (1934), etc., have given the reasons for believ¬ ing that ice-free shelters also existed in Greenland. Hadac (1948), A. & D. Love (1947, 1951), etc., have accepted the existence of refuges in Iceland. The presence of many species, especially boreo-atlantic, in the Faeroes could be explained by the assump¬ tion that they are survivors of the Ice Age (cf. Warming, 1902-3). As regards the origin of the mountain flora of the British Isles, the considerable number of the species (about 37) common to the British and ScandinaAuan mountains, but not occurring in those of Central and S. Europe, is in favour of the close relationship be¬ tween the two floras. This statement is in agreement with Wil- mott’s (1930) and Matthews’ views that the British mountain species are of Scandinavian affinity. It is very difficult to explain the occurrence of many of the above-mentioned species in Britain, especially those which in Scandinavia and other countries have been regarded as pre-glacial relicts. They could not immigrate there from Scandinavia or other boreal countries in the post-glacial period, because the British Isles had no land-connexions with these countries at that time. The remains of these plants have been found neither in deposits of the pre-glacial period in the unglaciated part of Britain (to the south of a line joining the Severn and the Thames) nor on the other side of the Channel. If the ice-free shelters existed in Greenland, which has been considered as the actual centre of the BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS 95 northern ice-sheet, when the glaciation was at its maximum, then it is evident that they should have been also to the north of the Thames. The existence of such unglaciated areas has been recognized by many authors here. Thus Wright (1914) showed that con¬ siderable areas of the Pennines and Yorkshire show no signs of ever having been covered by ice. His view was supported by Wilmott (1930, 1935), who pointed out that Upper Teesdale in the Pennines is remarkable for the number of rare plants occurring there to-day, e.g., Viola rupestris Schmidt, Minuartia strict a (Sw.) Hiern (neither is found elsewhere in the British Isles), Myosotis alpestris Schmidt, Dryas octopetala L., Gentiana verna L., Poten- tiila fruticosa L., as well as some southern species, such as Senecio spathulifolius Turcz., Helianthemum canurn (L.) Baumg., etc. According to him, these plants are survivors which had found a shelter in that station during the Ice Age. T. W. Woodhead (1924) regarded the heath vegetation of the Pennines as being of pre-glacial origin. As shown by Dandy and Taylor (1946), the occurrence of Potamogeton x suecicus Richt. in Yorkshire (in the rivers Ure and Wharf e) and in the river Tweed, outside the pre¬ sent area of one parent ( P . filijormis Pers.) and only rarely in as¬ sociation with the other (P. pectinatus L.), indicates that it also may be a glacial relict which has survived in the given localities. Wilmott considered that flat-topped mountains, which are characterized by rare plants to-day, have proved to be refuges. According to him (1935), there had also been refugees on the fol¬ lowing mountains: on Ben Bulben (in Ireland), which has Aren- aria ciliata L. (regarded by Ostenfeld & Dahl as an endemic sub¬ species — ssp. hibernica (Fig. 8)), Poly gala vulgaris var. grandi- flora Bab. [resembles var. Ballii (Nym.) Ostf., found only in the Faeroes] and a peculiar form of Thalictrum minus L.; on Ingle- borough (in Yorkshire) with Poa alpina L. and Arenaria gothica Fr. (Fig. 8), which has a striking discontinuous area, being found outside this locality only in Gotland and Vastergotland (Sweden) and in Switzerland; and in the Cross Fell area where Myosotis brevifolia C. E. Salmon (an endemic species) occurs. Also the Snowdon area (Caernarvon) includes some plants, e.g., Cerastium Edmondstonii, Saxifraga caespitosa, Poa alpina f. vivipara L., P. glauca and Lloydia serotina (L.) Rchb., the ranges of which give an indication that they may be relicts from pre¬ glacial and glacial times. It is interesting to note that Lloydia serotina does not occur in Scandinavia, but it has a striking dis¬ continuous circumpolar range [see the maps of the distribution given by N. Woodhead, 1933, 1951]. Much attention has been directed also to the flora of the Western Isles of Scotland (the Inner and Outer Hebrides, includ¬ ing St. Kilda), which are of considerable phytogeographical in¬ terest to students of the origin and history of the British flora, as shown by Turrill (1948) and J. Heslop Harrison (1948). Among 96 THE CHANGING FLORA OF BRITAIN the plants having a wide distribution in the British Isles, there are to be found many arctic-montane species, such as Cardamin- opsis petraea (L.) Hiit., Silene acaulis (L.) Jacq., Oxyria digyna (L.) Hill, Polygonum viviparum L., Desdhampsia alpina (L.) Roem. & Schult., etc., which often, as in Scotland, grow near sea- level, as well as some very local plants in the British Isles, e.g., Juncus pygmaeus Rich. (Lizard), J. capitatus Weig. (Land’s End, Lizard, Anglesey, Channel Islands) and Exaculum pusillum (Lam.) Caruel (cf. Turrill, 1948). There occur also several en¬ demic forms in the genera Orchis, Euphrasia, and Hieracium. The distribution of these plants indicates that some of them may be relicts of the pre-glacial flora. Also the occurrence of several American species having a restricted distribution in the British Isles is in favour of the assumption that many islands of the Inner and Outer Hebrides were unglaciated. They are: Erio- caulon septangulare With., found in Skye and Coll (also in Ireland, from W. Cork to W. Donegal), Spiranthes Romanzoffiana ssp. stricta (Sm.) Clapham, occurring in Colonsay and Coll (elsewhere in Ireland, from Lough Neagh in Londonderry, Antrim, Down and Armagh) and Potamogeton epihydrus Raf., recently discovered as a native in S. Uist in the Outer Hebrides ( J. W. Heslop Harrison, 1949; Taylor, 1949). One of the interesting islands of the Hebrides in connexion with the composition of the flora is Rhum in the Inner Hebrides, which seems never to have been glaciated. Some rare plants occur there, e.g. Arenaria norvegica Gunn, (known also from two localities in W. Scotland and in one in Shetland), Thlaspi cala- minare Lej. & Court, (known also from Matlock and other locali¬ ties in Derby), some very puzzling mossy saxifrages, and Euphrasia Heslop-Harrisonii Pugsley (elsewhere known only from W. Ross), as well as several endemic forms, such as Orchis Fuchsii ssp. rhumensis Heslop-Harrison 1, Euphrasia rhumica Pugsley, etc.* According to Turrill (1928) the isolated islands of St. Kilda also were not covered by an ice-sheet. In his study on the flora of these islands, he came to the conclusion that the main mass of the heath-moor vegetation had survived the Ice Age in the St. Kilda group. In his opinion at least five species might be wood¬ land relicts. As regards the Shetland Islands, it is found that Foula was partly covered by an ice-sheet, and a part of its vegetation may have survived there, as shown by Turrill (1929). The bulk of the plants common to the mountain floras of the British Isles and Scandinavia are distributed in Scotland. In addition, there occur several plants with restricted distribution in the Inner and Outer Hebrides and Shetland, as well as some *Carex bicolor All. recorded from the Isle of Rhum seems to be an introduced plant (cf. Raven, 1949). The status of C. glacialis Mackenzie as an indigenous plant in Rhum is also doubtful. BBITISH AND SCANDINAVIAN MOUNTAIN I'LOKAS 97 endemic forms, e.g. Calamagrostis scotica (Druce) Druce (Caith- ness), Roegneria Doniana (F. B. White) Meld. (Ben Lawers and adjacent mountains in Perth and near Inchnadamph in W. Sutherland; (cf. Melderis, 1950; Raven, 1952), Rhinanthus Lin- toni Wilmott mountains of Dunbarton, Angus and Perth), R. lochabrensis Wilmott (Glen Nevis), Primula scotica Hook. (W. Sutherland, Caithness and Orkney) and several species of Hiera- cium. The occurrence of Alopecurus alpinus Sm. in Scotland (on the higher Scottish mountains from Perth to E. Ross) is of particular interest. This species does not occur in Scandinavia, but it is found in Spitzbergen, Franz Josef Land, Novaya Zemlya, Kolguev, the Urals, N. Asia and N. America, as well as in Green¬ land, except the southern part (cf. Hulten, 1941). The distribu¬ tion of this and many other rare plants having a peculiar dis¬ continuous range outside the British Isles seems to indicate that they may have survived the Quaternary Period in Scotland in some sheltered ice-free situations (“nunataks”) near the sea coast. The distributional range of these species in Scotland is in¬ sufficiently known at present to determinate the possible locations of the shelters. Intensive studies on the ecology, variability and cyto-genetics of the Scottish plants may reveal many interesting facts concerning the origin and history of the British mountain flora. The data available to-day, however, lead to the suggestion that many plants seem to have been living in their present situa¬ tions during the Ice Age, and that they had arrived there at least before the last glaciation (cf. Matthews). Judging from the large element common to N. American and European floras, it seems that there was a connexion (the proximity of the continents, or continuity of arctic lands, or a land-bridge) between these two continents in the North Atlantic, also probably between Scotland and Scandinavia in the past (cf. Nordhagen, 1935). Different views as to the cause and the manner of disappear¬ ance of the connexion are held (cf. Wulff, 1944, 1950). There is also a wide divergence of opinion concerning the time when the separation of the countries may have taken place. Thus accord¬ ing to Thoroddsen (1914) the land connexion might have disap¬ peared in the late Miocene or at least before the beginning of the Ice Age, but according to Hadac during the Wurmian period. The history of the flora since the post-glacial epoch is much better known, owing to investigations of plant remains and pollen grains in the deposits, e.g. in peat-beds (Godwin, 1934). In his studies on immigration of the flora in Norway, Blytt (1876, 1882a, b) found that climatic conditions in the post-glacial epoch were characterized by alternation of warm and cool periods, which were either wet or dry, each being in turn advantageous to a particular group of plants. Later his theory was definitely established by results obtained by Semander (1892, 1910), etc., in the investigations of the peat-beds in Sweden. A similar Q 98 T11E CHANGING FLORA OF BRITAIN sequence of successions of the periods and plants has been found also in the British Isles, as shown by T. W. Woodhead (1929), Tansley (1939), Good (1945), etc. After the melting of the ice- sheet surrounding the shelters, the survivors occupied suitable situations where they mixed with plants following the retreat of the glaciers from the southern regions. When the climate became warmer, the mixed arctic- montane flora migrated northward or to the higher altitudes of the mountains. The localities left free were colonized by wood¬ land elements and thermophilous plants. Further climatic varia¬ tions caused changes in the species composition of the floras, as well as in the distribution of the species. Changes in the constitution of the mountain flora are at first influenced by climatic and edaphic factors which determine the distribution of the plants and can advance the origin of new types (modifications or genetically fixed forms). Studies of the mountain plants from the cytogenetic and taxonomic point of view have shown also that processes of evolution, viz. hybridiza¬ tion, polyploidy and mutation, associated with selection, are im¬ portant in the changes of the vegetational features of the moun¬ tain flora. Hybridity tends to increase the variability in populations by genetical recombination of characters. In many cases it results in destroying the limits between the species, producing inter¬ mediate forms. Hybrids are more easily recognized in field populations than in isolated herbarium specimens. Partially sterile hybrids, which have “empty” pollen grains, can produce a very polymorphic and more or less fertile offspring in back- crossing with the parent species, growing together with them in the field, as in Roegneria canina x mutabilis, observed by me in northern Sweden. Natural interspecific hybrids have been found in many genera of the mountain plants of both the British Isles and Scandinavia. In the British flora hybrids commonly occur in the genera Salix, Epilobium, Euphrasia and Carex (cf. Clapham, Tutin & Warburg, 1952). They are met with also in Cerastium (C. alpinum x vul- gatum ), Cochlearia ( C . officinalis x scotica), Saxifraga ( S . nivalis x stellaris, S. hypnoides x tridactylites, S. hirsuta x spathidaris, the latter of which does not occur in Scandinavia), Poa (P. x jemt- landica = P. alpina f. vivipara x flexuosa) etc. Several species have been regarded as having a hybrid origin, e.g. Orchis Francis- Drucei Wilmott (a hybrid derived from O. purpurella T. & T. A. Steph. and O. ericetorum (E. F. Linton) E. S. Marshall), Rhinanthus Lintoni and R. lochabrensis (probably offsprings of crossings be¬ tween R. borealis (Stern.) Druce and R. stenophyllus (Schur.) Druce or R. spadiceus Wilmott). In comparison with the Scan¬ dinavian flora, it is poorer in hybrids, but this can be explained by the fact that the Scandinavian mountain flora is richer in species, many of which have been much more fully investigated from the cytogenetic point of view. BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS 99 The role of hybridization, combined with gametophytic apomixis, in the origin of forms has been clearly demonstrated by Nygren (1950a, b) in his study on the species of Poa, occurring in the Scandinavian mountains. According to him, numerous forms of Poa have arisen in crossing between apomictic, faculta¬ tive sexual and sexual types. Some of them can propagate only by vegetative means, while others may produce new forms by crossing. Nygren (1950a, p. 232) mentions: “In this way the number of forms increases every year, provided that the outer conditions do not change”. It seems that the polymorphy of some apomictic groups in the mountain flora of the British Isles has arisen in the same way. Apomixis has been stated to occur in many genera, such as Alchemilla, Potentilla, Taraxacum , Agrostis, Calamagrostis, Des- champsia, Poa, Festuca, etc. (cf. Gustafsson, 1946, 1947a, b). A striking feature of the mountain flora is the occurrence of vivipary (replacing of flowers and spikelets by bulbils), which is more frequent in the Arctic flora. In the British mountain flora the vivipary occurs in Polygonum viviparum L., Saxifraga cernua L., Poa alpina f. vivipara L., P. x jemtlandica (Almq.) Richt., Festuca vivipara (L.) Sm.*, Deschampsia alpina (L.) Roem & Schult. and D. caespitosa (L.) Beauv. The same plants grow also in Scandinavia, but there viviparous forms are found also in some other species, such as Poa pratensis L. s. lat., P. arctica R.Br. (not occurring in Britain) as well as in a hybrid P. x herje- dalica H. Sm. (P. alpina f. vivipara x pratensis ssp. alpigena ) and Festuca rubra L. (cf. Nannfeldt, 1940). From the genetic point of view these viviparous plants may be comparable to the obligate apomicts, as pointed out by Stebbins (1950). Nannfeldt (1937, 1940) has shown that vivipary in Poa and in other grasses is a consequence neither of modification nor of hybri¬ dization. According to him, the ability to transform the spike- lets into bulbils is genetically fixed and associated with environ¬ mental conditions. As shown by Miintzing (1940), some vivipar¬ ous clones of Swiss Poa alpina may have originated by mutation from non-viviparous biotypes having the same chromosome num¬ ber and growing in the same locality. As to the abundance and distribution of these forms, Nann¬ feldt (1940, p. 32) has mentioned that “Non-viviparous biotypes are as a rule both more common and more widely distributed *Wilmott (1945) in his studies on F. vivipara from Uig (in the Outer Hebrides) has found that it is heterogeneous there. Some forms seem to be identical with ssp. faeroensis (Turesson) Wilmott and ssp. vaagensis (Turesson) Wil- mott, which is said by Turesson (1926-7) to be distributed in the Faeroes and Iceland. Some others show a close resemblance with ssp. jemtlandica (Tures¬ son) Wilmott, which, according to Turesson, is known from the Nor¬ wegian coast. In addition to them Wilmott has described ssp. uigensis known only from Uig. In the Scottish material of F. ovina Turesson ha* found two separate types, which have been treated by Wilmott as subspecies of F. vivipara, viz. ssp. killinensis (from Killin in Perthshire) and ssp. scotica (widely distributed in Scotland). 100 THE CHANGING FLORA OE BRITAIN than viviparous ones, but in certain high-mountainous areas, where the climatic and edaphic conditions are especially favour¬ able for viviparous strains, such may locally supersede the semi¬ niferous strains”. The exclusively viviparous species may occupy a rather large area. The viviparous form of Poa alpina in the British Isles is more frequent than the non-viviparous, which, as far as 1 know, has been recorded from four localities in Scotland (Lochnagar, Ben Lawers, Caenlochan and Glen Callater) and from one in York¬ shire (Ingleborough). It seems that the non-viviparous form of P. alpina was more widespread in the glacial period and has been now disappeared in many localities owing to the warmer climate. The viviparous forms probably may be more resistant to changes of climatic and edaphic conditions. As regards Scandinavia, non- viviparous P. alpina has a wide range there, being distributed everywhere in northern Scandinavia. It occurs also as a glacial relict in some parts of Central and S. Scandinavia, e.g. in some localities near Stockholm and Uppsala, on the islands of Oland and Gotland, where it grows on sunny cliffs. The viviparous forms of P. alpina on the contrary are frequent in the mountains of northern Scandinavia, but are absent in the southernmost mountains. As mentioned by Turesson (1926-7, 1929-30, 1931) in Festuca ovina and by Nygren (1949) in Deschampsia alpina, the forms showing the greatest degree of vivipary are those which have a higher chromosome number. Nygren (1949), as also Lawrence (1945), has succeeded in obtaining a viviparous form of Deschamp¬ sia caespitosa in cultivation of a normal type by changing the growing conditions — the length of day. Only the northernmost biotype, from 68° N. latitude (from Abisko in Lapland) culti¬ vated at 60° N. lat. (at Uppsala in Middle Sweden), being ex¬ posed to light for eight hours every day during two months, was affected as regards vivipary. The viviparous types of Deschamp¬ sia alpina, Festuca vivipara, F. rubra f. vivipara, Poa x jemt- landica, P. x herjedalica and P. arctica var. stricta in the same conditions preserved the vivipary even after the experiment. Nygren has arrived at the conclusion that the formation of bulbils in Deschampsia is due to variations in the length of daylight. His assumption is in agreement with Harder’s (1948) investiga¬ tions on Kalanchoe Blossfeldiana Poelln. According to Harder, the development of the flowers depends on special hormones, the formation of which are influenced by photoperiodism. Nygren writes (1949, p. 31): “Everything speaks in favour of different hormones and the moment of their action being genetically fixed and combined with a special life-rhythm. Disturbances of the normal rhythm — which may be of other kinds than in Deschamp¬ sia — will, depending on their degree, cause irregular meiosis, diplospory, apospory, or vivipary”. These experiments are a valuable explanation of the origin of the viviparous and apomic- tic forms. BRITISH AND SCANDINAVIAN MOUNTAIN FLORAS 101 The viviparous hybrids, e.g. in the genus Poa, can be pro¬ duced only in localities where one of the parents is represented by a viviparous form. It may be of interest to note, that the vivi¬ parous forms have usually well-developed pollen grains, but do not give seeds. The hybrids between a non-viviparous and a viviparous form are able to propagate themselves by bulbils, and therefore they are much commoner than the hybrids between non-viviparous species. Polyploidy is widespread both in the British and Scandin¬ avian mountain floras. Many authors, e.g. Tischler (1935), Love & Love (1943, 1949) and Flovik (1940), have studied the relation between polyploids and distribution. It has been found that fre¬ quency of polyploids increases with higher latitude, higher alti¬ tude or in extreme edaphic conditions. This phenomenon has been ascribed generally to the greater hardiness of polyploids, but this assumption has been criticized by several authors. Steb- bins (p. 347) has pointed out that “. . . no general rules can be formulated to govern the relation between the distribution of polyploids and diploids at least at present.” Tropical and Southern Hemisphere plants are still little investigated from the cytogenetic point of view in comparison with those of the tem¬ perate and arctic floras. According to him, the higher percentage of polyploids in northern latitudes could be explained by the fact that the floras of these regions contain a high percentage of perennial herbs (hemicryptophytes) which are more favourably disposed toward polyploidy than woody plants and annuals. The origin of polyploids may have been promoted by very drastic changes in climatic and edaphic conditions, especially during the Ice Age. As shown by many authors (cf. Stebbins), the poly¬ ploids possess wide ranges of tolerance of environmental condi¬ tions, and they are peculiarly fitted to occupy new areas, e.g. re¬ sulting from glacial recession. Due to these causes the floras of montane and boreal regions are rich in polyploids. The processes of mutation also play a considerable role in the changes of the mountain flora. The reasons for the origin of the mutants are still insufficiently investigated. It seems, however, that environmental factors, such as cold, heat, radiations and certain chemical substances in the soil could promote the changes in the hereditary material, associated sometimes with new charac¬ ters in the plants. Many of the mountain species and peculiar biotypes have such origin. The best known mutants are poly¬ ploids, which have originated by doubling of the chromosome set in a non-hybrid plant. Thus Arenaria norvegica (2n = 80) may have arisen from A. ciliata (2n = 40), Empetrum hermaphroditum (Lange) Hagerup (2n = 52) from E. nigrum L. (2n = 26) and Primula scotica (2n = 54)* from P. farinosa L. (2n=18). *It Is replaced by P scavdinavtca Bruun (?n=72) in Scandinavia (Norway). 102 THE CHANGING FLORA OF BRITAIN Floristic, cytogenetic and taxonomic investigations reveal that the British and Scandinavian mountain floras have a com¬ mon ancient history, and the changes in the species composition in both floras are influenced by the similar climatic and edaphic factors combined with processes of evolution. REFERENCES blytt, A., 1876, Essay on the immigration of the Norwegian flora during alter¬ nating rainy and dry periods. Rristiania. - , 1882a, Die Theorie der wechselnden kontinentalen and insularen Klimate, Engl. Bot. Jahrb., 2, 1-50. - , 1882b, Nachtrag zu der Abhandlung : Die Theorie der wechselnden kontinen¬ talen und insularen Klimate, ibid., 2, 177-184. - ,, 1893, Zur Geschichte der nordeuropaischen, besonders der norwegischen Flora, Engl. Bot. Jahrb., 17, Beiblatt 41, 1-30. BOcher, T. W., 1951, Distributions of plants in the circumpolar area in relation to ecological and historical factors, J. Ecol., 39, 376-395. Callen, E. O., 1952, Studies in the genus Euphrasia L., Rhodora, 54, 145-156. Clapham, A. R., Tutin. T. G., & Warburg, E. F., 1952, Flora of the British Isles. Cambridge. Dandy, J. E., & Taylor, G., 1946, An account of xPotamogeton suecicus Richt. in Yorkshire and the Tweed, Transact. Proc. Bot. Soc. Edinburgh, 34 , 348-360. Fernald, M. L., 1925, Persistence of plants in unglaciated areas of boreal America, Mem. Amer. Acad. Arts & Sci., 15/3. Flovik, K., 1940, Chromosome numbers and polyploidy within the flora of Spitz- bergen, Hereditas, 26 Fries, M., 1949, Den nordiska utbredningen av Lactuca alpina, Aconitum septen- trionale, Ranunculus platanifolius och Polygonatum verticillatum, Act. Phytogeograph. Suec., 24- Fries, Th. E., 1913, Botanische Untersuchungen im nordlichsten Schweden, Vetensk. o. prakt. unders. i Lappl. Flora o. Fauna, 2. Getting, P., 1934, Studies on the vascular plants of East Greenland between Franz Joseph Fjord and Dove Bay (Lat. 73° l5'-76° 20' N.), Medd. om Grant., 101/2 Godwin, H., 1934, Pollen Analysis. An outline of the problems and potentialities of the method, New Phytologist, 33. Good, R., 1947, The Geography of the Flowering Plants. London. Gustafsson, A., 1946, Apomixis in higher plants. I. The mechanism of apomixis, Lunds Univ. Arsskr. N.F. Avd. 2, 42. - , 1947a, Appomixis in higher plants. II. The casual aspect of apomixis, ibid., 43 - , 1947b, Apomixis in higher plants. III. Biotype and species formation, ibid., 44 Hadac, E., 1948, On the history of the flora of Iceland, Stud. Bot. Cechosl., 9. Hansen, A. M., 1904, Hvorledes har Norge faaet sit Plantedaekke, Naturen. Harder, R., 1948, Vegetative and reproductive development of Kalanchoe Bloss- feldiana as influenced by photoperiodism, Symp. Soc. Exp. Biol., II : Growth. Cambridge. Heslop Harrison, j., 1948, Recent researches on the flora and fauna of the Western Isles of Scotland and their biogeographical significance, Proc. Belfast N.H. 0. Flora of County Wicfilow. Dublin. Cheeseman. T. F., 1906. Manual of the Flora of New Zealand. Wellington, N Z. - , 1925, idem, Ed. 2. Cockayne, L., 1917, Notes on New Zealand floristic Botany, Trans. N.Z. Institute, 50, 72. Grierson, R., 1931, Clyde casuals, Glasgow Nat., 9, 27. Haussknecrt, C., 1884, Monographie der Gattung Fpilobium. Jena. Lee, J. R., 1933, Flora of the Clyde Area. Glasgow. Praeger, R. Li.., 1946, Additions to the knowledge of the Irish Flora, 1939-45, Proc. Roy. Irish Acad.. 51, B3, 27-51. - , 1909, A Tourist's Flora of the West, of Ireland. Dublin. - , 1934, The Botanist in Ireland. Dublin - -, 1950, Natural History of Ireland. Reports of the Botanical Society Sc Exchange Club of the British Isles, 1908-1919, 1928-1930. Reports of the Watson Botanical Exchange Club. Scully, R. W., 1916, Flora of County Kerry. Dublin. Watsonia, 1 and 2, 1949-51. Wilson, A., 1938, Flora of Westmorland. Arbroath. 168 THE CHANGING FIX)RA OF BRITAIN EPILOBIUM ADENOCAULON IN BRITAIN (Exhibit) G. M. Ash The exhibit attempted to show the remarkable spread of a North American Willow-herb in Britain after its identification in 1932. Although herbarium specimens were found to date back to 1891, from Leicester, it does not seem to have spread from there in the same way that it has spread in the south of England since 1932. Epilobium adenocaulcm Hausskn. was first described from North America in 1879 and was first identified in Europe from Poland in 1917. Since then it has been recorded from many other countries (including Prance this year, 1952), being first identified in Britain from Surrey in 1932. The exhibit included a series of maps of various dates showing its gradual spread through Britain, especially in the south, until, by 1952, it had been recorded from upwards of 32 vice-counties; with more records since then. A few sheets of herbarium specimens of historic interest were shown, together with some points of difference from our other Epilobiums. The status of Epilobium adenocaulon should not be confused with that of the numerous passing aliens introduced regularly and from time to time. There is no doubt that it has come to stay and that it has already changed the flora of Britain. Not only is it now the commonest willow-herb in many areas, but its great abund¬ ance where it does occur, and its exceptional variability in height (from 4 inches to 6 feet) have changed the aspect of many places. As an inoffensive garden and arable field weed, it is quite excep¬ tional among our native willow-herbs. The question is : — Why has it made such rapid progress in recent years whilst remaining more or less static near Leicester for 50 years ? In the discussion which followed, Dr. Heslop-Harrison said he was especially interested in Mr. Ash’s remarks about the enormous varia¬ tion, particularly in stature, of Epilobium adenocaulon in Britain. He asked whether he had attempted comparative cultivation of the species from different habitats, and, if so, whether the progeny of the ex¬ tremely tall and extremely dwarf forms converge to an intermediate stature when grown in the same habitat, or whether the size differen¬ tial persists. Mr. Ash replied that he had not attempted comparative cultivation but the species occurred under an extraordinary range of habitat conditions. EPILOBIUM ADENOCAULON IN BRITAIN 169 Mr. Ash distributed copies of a duplicated clavis to the British Epilobia to those present at the Conference with the object of facili¬ tating the detection of E. adenoeaulon in additional localities. It is thought that readers will be glad to have this available in a more per¬ manent form and it is therefore printed below. A SUGGESTED SHORT KEY TO THE SPECIES OF EPILOBIUM TO BE FOUND IN GREAT BRITAIN. 1 a. Creeping prostrate plants with sub-orhieular leaves and erect capsules . E. peduncular e A. Cunn. b. Small sub-glabrous alpine plants with procumbent or ascending stems; leaves acute . 2 c. Plants normally one foot high or more and erect . 3 2 a. Leaves narrow elliptical, mostly entire . E. anagallidifoUum Lam. b. Leaves ovate and toothed . E. alsinifolium Vill. 3 a. Flowers irregular, in long terminal leafless racemes. Petals spreading from the base . E. ( Chamaenerion ) angustifolum L. b. Flowers regular, axillary or in short racemes, leafy at the base. Petals erect at the base . 4 4 a. Stigma deeply 4-lobed . . 5 b. Stigma club-shaped . . . 8 5 a. Flowers large, leaves distinctly clasping the stem . E. hirsutum L. b. Flowers less than l cm. in diameter . 6 G a. Pubescence of the inflorescence consisting of patent glandular or eglan- dular hairs only; never adpressed. Lower parts of the stem generally covered with woolly hairs. Very variable . E. parvljlorum Schreb. b. Pubescence of the inflorescence consisting of numerous short patent glan¬ dular hairs with numerous crisped adpressed hairs . 7 7 a. Leaves short stalked, cordate at base with bayed teeth Flowers usually red . E. montanum L. b. Leaves lanceolate with cuneate base distinctly stalked; teeth forward directed. Flowers white in bud turning to rose colour . E. lanceolatum Seb. & Mauri 8 a. Pubescence of inflorescence predominantly of numerous adpressed hairs 9 h. Pubescence of inflorescence consisting of an equal proportion of patent glandular or eglandular hairs and adpressed ones . 10 9 a. Plant wholly without glandular hairs. Leaves generally parallel sided, their limbs decurrent down the stem, teeth acute, surface uneven and shiny . E. tetragonum Curt. b. Plant wholly without glandular hairs. Leaves lanceolate, narrowed to a short stalk, never decurrent, surface dull . E. Lamyi F. Schultz c. Plant always with a few patent glandular hairs on the calyx-tube. Leaves very variable . E. obscurum Schreb. 10. a. Leaves elliptical, distinctly stalked with a cuneate base, teeth numerous, degree of pubescence very variable. Seed without appendage . E. roseum Schreb. b. Leaves narrow lanceolate tapering at both ends, sessile, teeth very obscure or absent. Seed with an oblong pellucid appendage . E. palustre L. c. Leaves oblong-lanceolate with a cordate base, teeth numerous, petiole short. Flowers small and numerous; seeds with a rounded pellucid appendage . E. adenoeaulon Hausskn. 170 TIIE CHANGING FLORA OF BRITAIN In the identification of Willow-Herbs the quality of the pubescence is all im¬ portant; t lie quantity is unimportant, varying with the habitat. HYBRIDS. Hybrids occur very frequently in the genus and within limits generally exhibit characters intermediate between the two parents. The following charac¬ ters may help to pick out hybrids from true species. The characters are arranged in the order most noticeable. 1. Plant larger and, more branched than either parent. 2. Flowers larger than in either parent or alternatively diminutive. 3. Tips of the petals markedly deeper in colour. 4. Pods shortened and undeveloped. 5. Seeds mostly abortive n. Leaves intermediate in shape between the parents. 7. Pubescence intermediate in character, but variable. 8. Stigmas varying on different plants from shortly club-shaped to obscurely cruciform. It would be impracticable to draw up a key for all the numerous hybrids, but it is always a great help to know what true species were present at the site. A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREES AND SHRUBS 171 A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREES AND SHRUBS E. F. Warburg. When T was asked to speak at this conference I was more fortunate than some of yesterday’s speakers in that I was, at least partly, allowed to choose my subject. I asked to speak on alien woody plants because I felt that they had been much neglected in comparison with herbaceous ones. For example, even plants such as the casual brewer’s aliens at Burton-on-Trent, which have not become permanently established, have been more intensively studied than such permanent members of our flora as Quercus Cerris L. and Rhododendron ponticum L. of which, had this conference been held two months earlier, it could have been said that they did not figure in any British Flora. Other speakers have already told you about the natural changes that our climate and vegetation have undergone since the last glacial period and I do not propose to go into this further except to mention the importance of post-glacial research in elucidating the changing range of many species. Trees whose pollen is preserved are among the most satisfactory of these (e.g., the range of Fagus as a native tree has contracted considerably compared with earlier times). Another example based on rather different evidence which will be discussed later this afternoon is Buxus, and I shall return to similar points later. You have already heard that for a long period in the post-glacial the greater part of this country (especially that with which I am mainly concerned in that it is there that most of our woody aliens are to be found) was fairly completely covered with forest and that man has been responsible for the present open nature of the country. This process has, of course, been responsible for enormous quantitative changes in the area occupied by different species, and the isolation of our wood¬ lands must prevent to a large extent the spread of many species by natural means. There is, however, no evidence that man has been responsible for the extinction of any woody species. As an example of an indirect effect of this process one may perhaps quote the two species of Crataegus which Mr. A. D. Bradshaw has studied, and on which he will have something to say presently. Man has worked also in another way in introducing alien trees and shrubs, as follows : — 1. Forestry. Trees planted on a large scale for forestry are our native hard¬ woods, the sweet chestnut ( Castanea sativa Mill.) and perhaps the sycamore ( Acer Pseudo-platanus L.), a number of exotic conifers and our native Pinus sylvestris L. On the whole, these exotic 172 THE CHANGING FTyORA OF BRITAIN conifers, although they are now a permanent feature of our land¬ scape, have not become extensively naturalised. The European larch (Larix decidua Mill.) has probably been the most successful. Some of the western North American species have, however, been here only a comparatively short time and may yet spread, thus Pseudotsuga taxifolia (Poir.) Britt., the earliest of them, was in¬ troduced in 1827, and Thuja plicata Lamb, in 1853. Coniferous plantations do, however, contribute extensively to “The Changing Flora of Britain” by killing out the ground vegetation below them and must be ranked with the military, hydro-electric schemes, and building operations as the most important factors in the reduction of many native species. Of our native hardwoods, the beech may again be used as an example. Its native range to-day probably extends from south-east England to Hertfordshire, Gloucester¬ shire, Brecon, Glamorgan, Somerset and Dorset although it is planted extensively almost throughout the British Isles and re¬ generates freely in Aberdeenshire. 2. Ornament. It is probably among species which have been planted primarily for ornament that one must look for the greatest influx of woody aliens into our flora — a few examples which will not be discussed further are : — Amelanchier laevis Wieg. (extensively naturalised, for example, amongst native vegetation in the Hurt- wood, Surrey), Cotoneaster Simonsii Baker, Sorbus intermedia (Ehrh.) Pers. 3. Fruit. Fruit trees and shrubs present a special problem. Many have been cultivated for long periods (it would be interesting to know what light fossil evidence throws on the subject). Some are un¬ doubtedly native in this country although the wild form is not always the same (e.g., apple, sweet cherry). Others (e.g., pear, medlar) are almost certainly introduced; neither of these ever looks native as far as I know and the same is, in my experience, true of Prunus domestica L. which is probably not wild anywhere, though its subspecies insititia (L.) Poiret is often considered native. This subspecies seems to be a decreasing tree, perhaps owing to its being grown less than formerly, and the same is probably true of the sour Cherry (P. Cerasus L.). There appear to be no recently introduced fruit trees. 4. Other purposes. These can be taken as including : — (a) Hedges. Prunus cerasifera Ehrh. is an example. (The hedges of this in full flower are a feature of the countryside in spring, especially in East Anglia.) I have not seen it as a self- sown plant and know no reliable record of it as such; it fruits rarely and rather sparingly in this country. Fuchsia magellanica Lam. may also be quoted. A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREES AND SHRUBS 173 (b) Cover and food for game. Examples are Gaultheria tShal- lon Pursh and Mahonia Aquifolium (Pursli) Nutt, and perhaps also Rhododendron ponticum. (c) Reclamation of unfavourable soils and shelter belts . Examples are Acer Pseudo-plat anus L., Alnus incana (L.) lVioench, Pinus nigra Arnold subsp. nigra and P. mugo Turra. Unlike other types of alien discussed during this conference, accidentally introduced woody plants are probably unimportant and I can think of no example that has become established. (It is true that Phoenix dactytifera L. — the Date Palm — figures in Druce (1928) but it need not be considered seriously.) I would now like to discuss a few individual species. Acer P seudo-platanus L. (the Sycamore) is one of the longest naturalised trees introduced in historic times. It has been studied by Jones (1945) and the following account is taken from his paper. He shows that it was fairly certainly introduced to Scotland (Perthshire) in the 15th or at least the early 16th century. The first definite evidence for England is Lyte (1578) in Niewe Herball — “there is here and there a tree of it planted in England”, where¬ as Turner (1562) does not mention it as in England though he mentions it as occurring in Germany. A hundred years later, Evelyn (1662) suggests it is only suitable for “distant walks” on the grounds of its “Honey-dew leaves”. It had presumably be¬ come more common. Dr. Jones believes, however, that it did not become widely used in shelter belts, plantations, etc., until the end of the 18th century, the first flora to give “woods” as its habitat being Abbot’s of Bedfordshire (1798) and the first definite evi¬ dence of natural regeneration by Samuel Hayes (1794) in Co. Dublin. Since that time it has been extensively planted and now doubtless occurs in every vice-county in the British Isles, though there were nine for which Dr. Jones was unable to trace records. It is now, of course, frequent everywhere and occurs and fruits up to at least 1,600 ft. (in Shropshire). Cotoneaster microphylla Lindl. This Himalayan species was introduced into this country7 in 1824 (Bean, 1925) though the first definite record as a naturalised plant appears to be 1890, ac¬ cording to Druce (1932). It became “respectable” (a term the meaning of which will become clear later) apparently at a fairly early date. Localities where it occurs naturalised are usually given in detail in County Floras. Twelve southern and central English County Floras were chosen as being fairly comprehensive in their inclusion of aliens and reasonably modem — all having been published since 1895. These were: — Cornwall (Davey, 1909) with supplement (Thurston & Vigurs, 1922); Devon (Martin & Fraser, 1939); Somerset (Murray, 1896) with supplement (Mar¬ shall, 1914); Hampshire (Townsend, 1904) with supplement (Rayner, 1929); Sussex (Wolley-Dod, 1937); Kent (Hanbury & 0 174 THE CHANGING i-LOKA CH BRITAIN Marshall, 1899); Surrey (Salmon, 1931); Berkshire (Druce, 1897); Oxfordshire (Druce, 1927); Buckinghamshire (Druce, 1926); Gloucestershire (Riddelsdell, Hedley & Price, 1948); and Leices¬ tershire (Horwood & Noel, 1933). Out of these, Cotoneaster microphylla is mentioned in six and in each of these, except Corn¬ wall, its known localities are given in detail. There are 20 British specimens in the Oxford University Herbarium, which includes Druce’s. Its characteristic habitats in this country are rocky limestone pastures, limestone cliffs and, in contrast to the syca¬ more, it seems to be little planted outside gardens and must owe most of its spread to birds. Its recorded range by vice-counties is 1-4, 6, 9, 10, 13-15, 17, 33, 34, 38, 39, 41-45, 47, 50, 52, 56, 62, 65, 67, 69, 70, 80, 88-90, 103, 104. It would probably be fairly easy to map its known stations. It may be noted that it finds a place in both Druce (1932) and Butcher & Strudwick (1930). Rhododendron ponticum is chosen as a contrast to the last species. It is probably much commoner as a naturalised plant and is of much greater ecological importance. For example, in the Killarney oak woods it is replacing holly as the shrub layer over extensive areas and becoming a menace to the native vegeta¬ tion. All of you have doubtless observed the same sort of thing happening elsewhere. Its date of introduction was 1763, but it is not ‘respectable’ and I have not been able to trace its first record as a naturalised plant. Of the 12 county floras quoted it is only mentioned in one (Sussex) and there somewhat apologetically — “Though not usually recorded m county floras, the Rhododendron is as completely naturalised as Pinus sylvestris, Acer Pseudo- platanus, Castanea sativa and other planted trees. It occurs wherever it has been planted and reproduces itself freely from seed”. The flora of Surrey mentions the much rarer aliens Gaul- theria Shallon and Kalmia polifolia Wangenh., but does not men¬ tion Rhododendron. There are only five British specimens in Herb. Oxford. It is likely that the available data would be quite inadequate to give any picture of either its present-day range or its spread. Quercus Cerris L. is another extensively naturalised plant which occupies in “respectability” an intermediate position be¬ tween the two preceding; nine of the 12 county floras give it, but mostly without localities and some dismiss it as “planted”. Davey (1909) gives it as “perfectly naturalised in many parts” and this is probably true of most of the counties though Wolley- Dod (Sussex) says “very rare” and gives localities; three others give localities also but they are manifestly inadequate. There are 12 British specimens in Herb. Oxford. It is not in Druce (1932) nor in Butcher & Strudwick (1930). It was introduced in 1735. Buddleja Davidii Franch. This plant, which was introduced about 1890, is in a rather different category from the examples already given. Though occasionally recorded from woods and A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREKS AND SHRUBS 175 more frequently from railway banks before the last war, its main chance came during the war and it is now common on bombed sites in many places. How far it will persist as a naturalised plant remains to be seen. Before leaving the subject of undoubted aliens a few general points may be made. (1) There has been great un-evenness of treatment of woody aliens, which applies also to other aliens in some measure. Some have been regarded as “respectable”, others are not. (2) Where such aliens are mentioned, the presence or absence of natural regeneration and its extent are often not men¬ tioned. Contrast, for example, the bare statement ‘plantations’ for Q. Cerris in FI. Bucks, with the statement under Amelanchier laevis (as canadensis) in FI. Surrey — “naturalised over several square miles in the Hurtwood” — but even this gives no real idea of the plant’s abundance and this Flora does not mention Rhodo¬ dendron ! I would like at this point to put in a plea that more study should be given to woody aliens of all kinds and that where speci¬ mens are preserved they should be accompanied by full data of the occurrence and amount of regeneration. (3) It would be interesting to know what factors have caused the success of certain plants rather than of their relatives. Why is Rhododendron ponticum the only member of that genus to have spread extensively? A possibility is that it is the only one much planted outside gardens and that it is also used as a stock for grafting. Why has Cotoneaster microphylla spread freely and not C. frigida Lindl., which was introduced at the same time, is very widely grown, and fruits abundantly? Why are there no naturalised Berberis except B. vulgaris ? Much clearly depends on the extent of planting. (4) Is the large amount of planting along the new roads at the present time of many exotic shrubs going to have an effect? I hope careful records are being kept. I now want to turn to a more difficult and in some ways more important subject — that of ascertaining the native range or status of certain plants. It has been touched on earlier. The status of many of our trees is in question, thus Populus nigra L. and P. canescens Sm. may or may not be native trees. I want to take as an example Sorbus Aria (L.) Crantz. This is an unquestionably native tree but it has been extensively planted, since it is very ornamental. Its range by vice-counties, according to Druce (1932), adding to this such additions as have been made since, is shown in the accompanying map (Fig. 22). It will be seen that this range extends over the greater part of the British Isles. Its true range as a native plant, as far as I have been able to ascertain it, is shown on Fig. 21. S. Aria is thus confined to a i continuous area in the south-east of the country. This fits in with its 176 THE CHANGING FLORA OF BRITAIN 5 t£ e •^4 •c t- © o e — k •c V. © »3 c4 v. ®» c SS c ^ S 2 .* i: © i. © •*» 2 50 o « a) o a> > 2 A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREES AND SHRUBS 177 European range; it is a Continental species. It also occurs, ap¬ parently native, in Galway. In this it agrees with certain other calcicole species which occur mainly in the east of Great Britain but which also occur in isolated localities in Ireland (e.g., Viola stagnina. Kit., Helianthemum Chamaecistus Mill., Astragalus danicus Retz., etc.). This, however, is not relevant to this paper. The reason for the discrepancy is two-fold : — (a) Confusion between S. Aria and allied species. This is re¬ sponsible for many of the records from W. & N. England, some Scottish and many Irish records. (b) Records of naturalised or even planted trees which have not been separated from native ones. This is responsible for all the records from E. England, most of the Scottish ones and many of those from elsewhere. It has probably been more important than (a). The evidence for the native range is mainly based on personal field observations supplemented by county Floras. The latter, if properly used, are a great help in this type of work. One can get from them a good idea of the habitats and occurrences of the plant in the county in question. The actual statements in them, how¬ ever, of the status of the plant are of less value and must be care¬ fully sifted, being often based on preconceived ideas. Two types of evidence, valuable in other cases, seem to be of little use here. Herbarium specimens are usually unaccompanied by details of status and regeneration and are thus only of value in sorting out the records of non-native S. Aria from native stations of other species. As far as I know there are no fossil records for S. Aria and, even if it were found fossil, it would be unlikely that its remains would be separable from those of related species. The same applies to philological evidence. Another vexed and now probably insoluble problem, is pre¬ sented by Pinus sylvestris. It is universally acknowledged to be native in Scotland and the woods in such areas as the Spey Valley and Glen Affric certainly represent the remains of the old Cale¬ donian Forest. The Scottish plant, also, is a separate geographi¬ cal race. Until recently P. sylvestris was almost universally be¬ lieved to be introduced in England. In recent years fossil (pine pollen occurs throughout post-glacial deposits) and other evidence suggests that the pine may have persisted in England and that relicts may exist. Dr. A. S. Watt and I, in some work done during the war, reached the conclusion, based partly on the form of the trees and partly on other evidence, such as the presence of Goodyera repens (L.) Br., that certain Norfolk pines may well be such relics. It is possible that a combined study of the plants in situ , of fossil evidence and a comparison of the morphological features of British plants with known foreign races, and perhaps also philological and historical evidence, might enable definite conclusions to be drawn. There are in this country a limited number of woody plants which are never planted and perhaps these may be useful pointers. L 178 THE CHANGING FLORA OF BRITAIN I may perhaps again consider Sorbus. Apart from S. Aria, S. Aucuparia L., their hybrid, and perhaps S. torminalis (L.) Crantz, our native species do not seem to have been planted. Most of them are to-day plants of limestone cliffs but are heavily grazed by sheep when they can reach them and they may have formerly extended to other habitats as, in fact, S. hibernica E. F. Warburg still does. They may be put into two main groups (1) compara¬ tively widespread, (2) local endemics. The most widespread of them is S. rupicola (Syme) Hedl. and it is the only one which occurs in an apparently identical form on 12 8 58 52 50 English Miles 0 20 40 60 80 100 I - I - 1 - 1 _ l_| Kilometres 0 25 50 75 100 ISO U, ,t I — A .1 . J ✓< Kb 0 1 j Ju ft r'O / A J / c 6 Longitude \tfcst 4 of Greenwich 2 Fig. 23. The distribution of Sorbus anglica. 0 A CHANGING FLORA AS SHOWN IN THE STATUS OF OUR TREES AND SHRUBS 179 the Continent, where it occurs in Scandinavia. It has a number of isolated localities in W. & N. England, Wales, Scotland, and N. & W. Ireland. Another example is Sorbus anglica Hedl. which is known from the Wye Valley, where there are several stations, and from seven other localities in S.W. England, Wales and Kerry (see fig. 23). Though endemic, it has near allies on the Continent : — S. Mougeotii Soy.-Willem. & Godr. from the W. Alps; S. austriaca (Beck) Hedl. from the E. Alps, and S. subsimilis Hedl. from Nor¬ way. This may perhaps be an example of a species more wide¬ spread in the post-glacial that had become fragmented and differentiated. Minor differences exist in the British forms also. It may be compared with Veronica spicata L. subsp. hybrida (L.) E. F. Warburg and Helianthemum canum (L.) Baumg., already referred to by other speakers. It should, however, be mentioned that this group of Sorbus is probably apomictic. Narrow endemics include S. minima (Ley) Hedl., confined to limestone cliffs near Crickhowell (Brecon) and S. bristoliensis Wil- mott of the Avon Gorge. Both these are triploid and apomictic and perhaps originated by hybridisation not far from where they exist to-day. It is remarkable that they have not been spread further by birds, particularly in the light of the spread of such plants as Cotoneaster microphylla referred to earlier. Ulmus is another woody genus in which endemics occur, though they have been more extensively planted. I think that studies of such endemic species taken in con¬ junction with studies of woody aliens may help towards an under¬ standing of the large and difficult group of man-assisted species. REFERENCES. Bean, W. J., 1925, Trees and Shrubs hardy in the British Isles, ed. 4. London. Butcher, R. W., & Strudwick, F. E., 1930, Further Illustrations of British Plants. Ashford. Davey, F. H., 1909, Flora of Cornwall. Penryn. Druce, G. C., 1897, The Flora of Berkshire. Oxford. - , 1926, The Flora of Buckinghamshire. Arbroath. - , 1927, The Flora of Oxfordshire, ed. 2. Oxford. - , 1928, British Plant List, ed. 2. Arbroath. - , 1932, The Comital Flora of the British Isles. Arbroath. Hanbury, F. J., & Marshall, E. S., 1899, Flora of Kent. London. Horwood, A. R., & Noel, C. W. F., 1933, The Flora of Leicestershire and Rutland. London. Jones, E. W., 1945, Acer pseudo-platanus, in Biological Flora of the British Isles, J. Ecol., 32 , 220-237. Marshall, E. S., 1914, A Supplement to the Flora of Somerset. Taunton. Martin, W. K., & Fraser, G. T., 1939, Flora of Devon. Arbroath. Murray, R. P., 1896, The Flora of Somerset. Taunton. Rayner, j. F., 1929, A Supplement to Frederick Townsend's Flora of Hampshire. Southampton. Riddelsdell, H. J., Hedley, G. W., & Price, w. R., 1948, Flora of Gloucestershire. Cheltenham. Salmon, C. E., 1931, Flora of Surrey. London. Thurston, E., & Vigurs, C. C., 1922, A Supplement to F. Hamilton Davey's Flora of Cornwall. Truro. Townsend, F., 1904, Flora of Hampshire, ed. 2. London. Wolley-Dod, A. H., 1937, Flora of Sussex. Hastings. 180 THE CHANGING FLORA OF BRITAIN Dii. Melville then spoke on “ Some Historical Factors in the Dis¬ tribution of British Elms ” as follows: — Historical factors have played an important part in the distribution of the British elms. Some species, among which are Ulmus procera Salisb. and U. cornubieiisis Weston (U . stricta Lindl.) appear to have colonised our land from the south. In glacial times the English Channel and the continental shelf, now occupied by the Bay of Biscay, were dry land, owing to the general lowering of the sea level by about 300 feet and an isostatic rise in the earth’s surface in this area. Here the climate would have been suitable for the survival of elms, and on the passing of the glacial epoch and gradual flooding of the continental shelf, the elms could migrate northwards and colonise southern England. The remaining British species or their progenitors probably migrated westward from the Continent across the North Sea area be¬ fore it became flooded. The Wych Elm, U. glabra Huds., being the hardiest, probably came first and in due course extended its range throughout Great Britain. The remaining species, including U. Plotii Druce, U. coritana Melville and U. carpinifolia Gled., were probably later arrivals. They spread out over East Anglia and the Midlands and a mixed population of hybrids must have developed at an early date. All the species inhabiting this part of the country are inter- fertile and hybridise freely, with the exception of U . procera , which flowers before the other species and usually has its fruits destroyed by cold. The resultant hybrid swarms are still with us, but other historical factors have played a part in determining their present composition and distribution. We now find in East Anglia, especially in Essex and the adjacent part of Hertfordshire, that each valley contains its own hybrid form. On passing over the ridge into the next valley a different hybrid form is encountered, and so on with the next one. In some of the larger valleys the elm population changes as one proceeds down the valley, although the forms occurring in one valley are gener¬ ally closely related to one another. It is evident that this diversifica¬ tion must have arisen since the Ice Age. since at the time of the last glaciation conditions were unsuitable for the growth of elms in cen¬ tral and eastern England. The elm is a moisture-loving tree favour¬ ing the valley bottoms. This would lead to partial isolation of the valley elm populations even when this part of the country was com¬ pletely forested, as it doubtless was in Neolithic times. At a later stage man played a part in making the isolation more complete. It was easier for early man to clear the drier hill tops than the ranker growth in the valleys. Once this had been achieved, the valley elm populations were virtually isolated, since in these wind pollinated trees the concentration of pollen from the local population would have been far higher than that brought by air currents from neighbouring valleys. In spite of the clearing of the remaining forests from the valley bottoms at still later dates, the elm populations have remained essentially natural. Their propensity for producing suckers has enabled them to survive in hedgerows. HUMAN INFLUENCE! ON H YimiDISATION IN CllATAEUUS 181 HUMAN INFLUENCE ON HYBRIDISATION IN CRATAEGUS (Exhibit) A. D. Bradshaw. The taxonomy of Crataegus in Britain is difficult. It has been recognised that this is because C. monogyna and C. oxyacanthoides hybridise and give rise to intermediate forms. C. monogyna Jacq. is common in open scrub and hedgerows on a wide variety of soils, from heavy clays to dry chalks. C. oxya¬ canthoides Thuill. is restricted to the heavy clay soils of the Mid¬ lands and S.E. England. Various characters, such as capacity for flowering in dense shade, spreading growth-habit and well ar¬ ranged leaf mosaic suggest that it is primarily adapted to wood¬ land environments. C. monogyna seems unable to tolerate the extreme woodland environment in which C. oxyacanthoides is found. It is, for instance, unable to produce any flowers at all in dense shade. The evidence for hybridisation is not direct, since so far no artificially produced hybrids have been grown to maturity. But in undisturbed woodlands it is possible to find pure populations of C. oxyacanthoides , and, in open scrub, pure populations of C. monogyna. Whenever two such populations are in contact, the intermediate forms occur as a zone between them, suggesting their origin by hybridisation. Although there is a difference in their flowering times, there is ample opportunity for intercrossing be¬ tween the two species. A large number of artificial crosses has shown that fertile seed is set as easily in crosses made between the two species as in crosses made within the species. It appears that under original undisturbed woodland condi¬ tions the two species were ecologically isolated, neither being able to tolerate the proper habitat of the other. But the effect of man’s destruction of woodlands has been to destroy this isolation. By making clearings in woodland he has made areas which C. mono¬ gyna has been able to invade, and which has brought it in close contact with the woodland C. oxyacanthoides. By selective felling and undergrowth clearance, he has reduced the density of the woodland sufficiently to allow C. monogyna to invade the wood¬ land itself. As a result, populations with large numbers of hybrids have been developed in disturbed woodlands. This is a similar situation to that in Melandrium (Baker, 1948). The amount and nature of man’s disturbance of woodland has varied. Thus, by examination of different woodlands, it has been possible to find populations with different degrees of hybrid¬ isation. For comparison of such populations, individual plants were measured for one character only, that of the degree of inden¬ tation of the leaves. This has always been held to be an extremely THE CHANGING FLORA OF BRITAIN Fig. 24. Degree of Leaf Indentation in Populations of Crataegus. A. Horish Wood, Maidstone, Kent. On Gault clay. Carefully managed dense hazel coppice with oak standards. Pure C. oxyacanthoides. Upchurch, Rainham, Kent. In disused chalk pit. Open scrub with roses, etc. Pure C. monogyna. B. Buff Wood, W. Cambs. On heavy boulder clay. Badly managed mixture of oaks and hawthorn and hazel scrub. C. oxyacanthoides, many hybrids, and some C. monogyna. C. The Forest, Ashford, Kent. On Weald clay. Badly managed very open oak wood with scattered hawthorns and much open ground. Few C. oxyacan¬ thoides, many hybrids, and C. monogyna. D. Barton Close, Cambridge. On heavy boulder clay. Old hedge in town. Traces of C. oxyacanthoides, but mostly hybrids. J HUMAN INFLUENCE ON HYBRIDISATION IN CRATAEGUS 183 good diagnostic character for the two species and is closely cor¬ related with other diagnostic characters such as seed number, flowering time, growth habit, flower shape. It is not affected by the environment to any extent. The population values have been made into frequency distribution diagrams. Pure C. oxyacanthoides populations give a diagram shape such as that of Horish Wood, pure C. monogyna populations that of Upchurch (fig. 24a). Woodlands on the Gault clay belt of the North Downs that have been carefully managed as coppice and standards for a con¬ siderable period, such as Horish (fig. 24a), Longham and others also near Maidstone, Kent, maintain an almost pure population of C. oxyacanthoides. A similar situation is found in the middle of Buff Wood in W. Cambs., on heavy boulder clay, which has been maintained as dense high forest with only a little coppice. In woods that have been considerably disturbed such as the northern end of Buff Wood (fig. 24b) which is a confused mixture of hawthorn scrub and scattered oaks, and The Forest near Ash¬ ford, Kent, (fig. 24c) which is an open wood with few standard oaks and much open ground, there has been ample opportunity for intermixing of the two species and this has resulted in popula¬ tions consisting largely of hybrids. The population from Upchurch near Rainham, Kent (fig. 24a) is an example of a normal C. monogyna population outside the normal distribution of C. oxyacanthoides, and therefore quite pure. It is possible to find small populations of hawthorns in built-up areas in town, relics of former natural populations. These are usually of C. monogyna. But the population of Barton Close, Cambridge (fig. 24d) has an element tending towards C. oxyacan¬ thoides. The bushes are part of an old hedge whose origin was probably from cuttings from the hybrid scrub plants found on the edges of the woods on the heavy clay to the west of the town. Many such hedges are to be found north of London. A similar population was found in Winnington Road, High- gate, London, N.2, consisting of scattered bushes in various pri¬ vate gardens. The older Ordnance Survey maps show that these are on the site of the old Bishop’s Wood now no longer in exist¬ ence. This wood presumably had a good C. oxyacanthoides population, in common with other similar woods on London Clay. When forest cover was continuous it seems that C. oxyacan¬ thoides was very common on heavy clay soils. With the destruc¬ tion of woodland not only causing the loss of suitable habitats for it, but also allowing the introgressive hybridisation with C. monogyna, pure populations of C. oxyacanthoides are becoming increasingly uncommon. There is little doubt that this process will continue. REFERENCE. Baker, H. G., 1948, Stapes in invasion and replacement demonstrated by species of Melandrium, J. Ecol., 36. 96-119. 184 THE CHANGING FT.OBA OP BRITAIN IS THE BOX-TREE A NATIVE OF ENGLAND? (Exhibit) C. D. Pigott and S. M. Walters. The native status of Box ( Buxus sempervirens L.) in this country has often been questioned, and although most authorities have been inclined to accept it as native in a few famous localities such as Box Hill, the doubt persists in the literature. Thus Elwes and Henry (1913) wrote: — “Whether Box is native of England or not is doubtful; but it is certainly naturalised, if not truly in¬ digenous, in a few localities . . . .” And Tansley (1939) wrote: — “occurs apparently wild on chalk and oolite of the south of Eng¬ land. Doubt has often been thrown on its nativity; it is absent from the north of France except where it has been planted; and since its wood is valuable, it is one of the plants that may have been introduced by the Romans”. Two main arguments seem to underlie the doubt: firstly, that, because the word ‘box’ is a loan-word from the Latin “buxus”, the plant was introduced by the Romans (cf. Chari esworth (1949)); and, secondly, that ‘Box is absent from the north of France except where planted’. Let us consider these in turn: — 1. Evidence from the name. Although some 19th century philologists (e.g. Hehn (1870)) developed the argument that where a loan-word exists in a modem language, the object concerned had been introduced by the people from whose language the word had been borrowed, later authori¬ ties (e.g. Schrader, in Hehn, ed. 6 (1894)) pointed out that, although this might be true in certain cases, it is by no means necessarily so, and can indeed often be demonstrably false. Schrader emphasises instead, that a new use or significance intro¬ duced by the invading culture may suffice to plant a loan-word into the language for an object (plant, animal, etc.) already known to the native population. The Latin “buxus” is itself generally considered to be a loan-word from the Greek ( 7 rv£os) ; and this is readily understandable in view of the fact that there was a flourishing Greek trade in box- wood in the Eastern Mediterranean and the Black Sea centuries before Christ. In most European languages the word is obviously a derivative of this Graeco-Latin word; and whatever its precise history, it seems clear that its presence in English, French, German and elsewhere can tell us nothing directly about the origin of the Box-tree. The absence of any trace of a pre-Roman (Celtic) word for the plant in Britain or France is worthy of comment; but the explanation may well be that any pre-Roman word was already of the “buxus” type and was simply submerged by the Latin form. (There are actually IS THE BOX-TREE A NATIVE OF ENGLAND 185 traces of a very ancient pre- Indo-European word for the Box- tree in the Basque “ ezpel ” and a similar root in certain Southern French dialects and place-names; but the subject is highly obscure ! ) It is certainly not possible to believe that primitive peoples in Britain and France had no word for the plant; for there is abundant evidence that Box foliage, like that of other evergreens, has since the birth of civilisation in Europe been asso¬ ciated with religious rites, and particularly with burials — indeed the Christian Church has taken over this significance, as in the use of Box as an Easter “palm” in France, Belgium, and parts of Eastern Europe to-day (cf. the Romano-British burials with Box twigs). 2. Distribution and Status of Box. Tansley’s statement about Box in N. France seems to be trace¬ able, via Elwes and Henry, to a short paper by Chatin (1861), in which he discusses plants in northern France associated with gardens, chateaux, etc., to most of which he assigns a Roman introduction. Box is only mentioned casually, with a guess that the “introduction” of the plant dates principally from medieval rather than Roman times; in evidence he gives a short list of localities in the Paris region, in many of which there is a medieval chateau or monastery. The correlation appears to be there: but 186 THE CHANGING FLORA OF BRITAIN a likelier explanation than the one of medieval introduction is that those who built castles in the Middle Ages tended to choose the edges of cliffs or steep slopes, the most striking of which in the Paris area occur where the Seine erodes hard chalk (as at Les Andelys, or La Roche-Guyon) — precisely the localities where native Box might be expected! There seems really little doubt that in the Paris area, as in the Ardennes to the east and south Normandy in the west, there is native Box in very similar situ¬ ations to its classical British localities (cf. Lemee, 1935); and in¬ deed several French local floras have treated the plant as native in such places. The absence of Box from the Pas de Calais and most of Normandy may well be due firstly to the absence of suit¬ able steep chalk slopes or cliffs, and secondly to the intensive cultivation of the chalk areas. The general distribution of Box at its N.W. limit in Europe is in fact very closely paralleled by several other sub-Mediterranean species (as was pointed out by Engler in Schrader 1894). History of Box in France and England. Neolithic charcoal referable with reasonable certainty to Box has been recorded from Whitehawk Camp, near Brighton, and Iron Age charcoal probably of Box from Cissbury Camp, near Worthing. In addition there are several records of Box foliage in Romano-British burials on the chalk in Cambridgeshire and Berkshire. The plant was well known in Anglo-Saxon times; records of the Box tree and particularly of place-names with Box in them are found from the 8th century onwards. The evidence for the antiquity of certain present-day localities for Box is quite impressive ; even that on Sidon Hill, near Highclere, Hants, which Bromfield (1849) said was “an evident, and indeed acknowledged introduction”, can be shown to have been represented by at least one Box-tree in A.D.934! (Kemble, 1849). The majority of Eng¬ lish and French place-names derived from the word for “box” are 12th to 14th century in origin; and although it is true that, particularly in France, Box-groves were planted for their valuable wood, nevertheless the distribution of these place-names fits so well the areas where (in England) ancient Box records are avail¬ able and where the most likely native habitats persist, that one feels the planting has supplemented rather than radically altered an earlier distribution. It is interesting that Dauzat (1939), studying the evidence of pre-history afforded by place-names in the region south of Chartres known as “La Beauce” comments on the ‘box’ place-names which are not infrequent there, but be¬ cause of the rarity or absence of Box to-day in the region, he thinks the names cannot apply to Box. His general thesis, how¬ ever, is that all the evidence from different studies points to an early historical period of forest and clearing with relatively little cultivation, and he points out that place-names based on other trees are frequent. It would seem that, not only in La Beauce PLATE V. Photo by J. E. Lousley Interior of the Box wood on the steep slope above the River Mole, Box Hill Surrey. IS THE BOX-TREE A NATIVE OF ENGLAND 187 but also throughout the range of Box in France and England, the Neolithic and subsequent forest clearings gave to the plant, as to many others, a very considerable chance of spread, particularly in scrub vegetation on chalk, and that, by Roman times, the plant might well have achieved considerable abundance (cf. the Romano-British Box in graves). Later a developing use of the wood of the tree might well have led to its cutting out, and then to its artificial planting. When in such a picture do we assume that Box entered Britain? There is a (not certain) record for its pollen from a British interglacial deposit (on the Continent there are several interglacial finds); but we have no post-glacial sub-fossil record. We can therefore only guess; but a limited entry in the Boreal period, with a very restricted survival through the Atlantic forest maximum, would seem to be a reasonable guess. The dry Sub-boreal, with the Neolithic forest clearance, would then give the plant the chance of a secondary spread, which was probably very considerable. On such a hypothesis there would be three types of present-day Box locality: — 1. “Native” localities where the plant might have persisted since the Boreal; the steep chalk slopes of Box Hill are a good example. Here the rounded downs are interrupted by the gap cut by the river Mole and above Burford Bridge the river is actively undercutting the chalk escarpment (Plate V). It is sug¬ gested that the occurrence of Buxus in this locality is related to the topographical features, which have prevented the establish¬ ment of closed forest, and allowed the Buxus-Taxus wood to sur¬ vive the ‘Forest Maximum’. Although the young bushes of Buxus can grow n deep shade, examination of the wood suggests that only vigorous bushes in more open parts can produce viable seeds. The unstable nature of the chalk substratum is demonstrated by the accumulation of banks of chalk rubble on the upper side of the bushes and the exposure of the roots on the downhill side. 2. Survival of “scrub” localities of Neolithic or post-Neo- lithic origin; could not Box on ancient trackways such as Fleam and Devil’s Dyke date back to this period? 3. Box planted in historic time; possibly associated with Roman villas, medieval Box groves for wood, more recent plant¬ ing in shrubberies. REFERENCES. Bromfield, w. A., 1849, Phytologtst, 4, 817. Charlesworth, M., 1949, The Lost Province or The Worth of Britain. Cardiff. Chatin, a., 1861, Bull. Soc. Bot. France , 8, 364. Dauzat, A., 1939, La Toponymie Franqaise. Paris. Elwes, H. J., & Henry, A., 1913, The Trees of Great Britain and Ireland, 7. 1724- 30. Edinburgh. Hehn, V., 1870, Kulturpflanzen und Hausthiere . . . Berlin. Kemble, J. M., 1839, Codex Diplomattcus Anglosaxonicvs, 5, 196, line 14. London. Schrader, O., 1894, Kulturpflanzen und Hausthiere . . . (see Hehn), Ed. 6. Berlin. Tanslet, A. G., 1939, The British Islands and their Vegetation. Cambridge. 188 THE CHANGING FLORA OF BRITAIN THE CONSERVATION OF BRITISH VEGETATION AND SPECIES Sir Arthur Tansley (Chairman of the Nature Conservancy, 1949-53). During this Conference we have heard a great deal about the various factors that have contributed, and are contributing, to changes in our flora. For my part, I have been asked to talk about the means of conserving what can still be prevented from disappearing altogether. For though we cannot stop, or even check, the continuous introduction of fresh aliens (and I imagine that most botanists would not wish to if they could), we shall all agree, I think, in wanting to preserve as much of the native flora as we can. At this Conference, I am deliberately omitting reference to the conservation of animal life, though much of the Nature Conservancy's work is devoted to that, particularly of birds and insects. The motives of this desire are twofold. First there is the sentiment attaching to things (or most of them) which are native to Britain, intensified by a keen appreciation of the beauty and interest of many of them. We want to keep our old buildings when they are good-looking or specially characteristic of a crea¬ tive age. And we do not like to see our natural landscapes, such of them as still remain, destroyed or defaced — nor our man-made rural landscapes either, with their arable and pasture, coppice and hedgerow. The second motive is scientific interest in flora and vegetation, a motive which is specific to botanists and ecologists. With this second motive the Nature Conservancy is specially concerned, largely owing to the keenness and drive of its first Director-General, Cyril Diver, who stressed the scientific and practical importance of preserving as much as possible of the native flora and fauna and thus “cashed in”, as it were, on the current high prestige of science to persuade the Scientific Ad¬ visory Council to the Cabinet, and through them the late Govern¬ ment, to set up the Conservancy. Nevertheless, as I have often said and written, I personally find it hard to separate the two motives within my own mind — love of the British landscapes and their plant covering on the one hand, and, on the other, interest in studying them and finding out more about them: each of these motives, in my own experience, reinforces the other. Besides innumerable local bodies, and setting aside for the moment the National Trust, we now have four organisations of national scope concerned in conservation; two voluntary and two which are minor Government departments. The Society for the Promotion of Nature Reserves, founded by Charles Roths¬ child, has been at work for a good many years now, owns several THE CONSERVATION OE BRITISH VEGETATION AND SPECIES 189 reserves and has assisted several others. The Council for the Preservation of Rural England, as its name implies, has different and wider aims. Together with its sister body, the Council for the Preservation of Rural Wales, it works largely through pro¬ paganda and by calling public attention to the most various threats to the beauty of the countryside. Under many difficul¬ ties and without any state assistance, it has done, and is doing, yeoman work on these lines. Of the two Government bodies, the National Parks Commission was set up under the National Parks and Access to the Countryside Act of 1949. It is respons¬ ible for the designation of National Parks, which are tracts of largely wild country primarily intended for the enjoyment of the public. The Commission was placed under the Ministry of Town and Country Planning, now renamed the Ministry of Housing and Local Government (a significant change of title). It was this Ministry that set up in 1945 the National Parks Committee, un¬ der the chairmanship of Sir Arthur Hobhouse, and the adjunct Wild Life Conservation Special Committee, on whose reports the Act which established the National Parks Commission was based. Unfortunately, as many people think, the Commission has little executive authority, as it was originally intended they should have. The actual management of the National Parks will rest with Local Planning Boards appointed mainly by local autho¬ rities, the National Commission acting as an advisory body to the Local Planning Boards, which must consult it, and to which it can make recommendations, but on which it cannot enforce its views. Both the C.P.R.E. and the N.P.C. are commonly referred to as “amenity bodies”, or (privately) by the often somewhat hard- faced “practical man” as “those amenity people”. Finally there is the Nature Conservancy, established early in 1949 by Royal Charter and given statutory duties and powers in the same Act as that which created the National Parks Com¬ mission at the end of that year. The Conservancy works under the aegis of the Committee of the Privy Council which also sponsors the Agricultural Research Council. But the Conser¬ vancy is directly responsible to the Lord President, who, in turn, is responsible for it to Parliament. The main headquarters of the Conservancy is in London, but there is a Scottish headquarters in Edinburgh and a Scottish Committee which deals with conservation in Scotland. The Conservancy, consisting of 18 members, mainly biologists, geologists, or geographers, but including 3 Members of Parlia¬ ment, meets four times a year, one of these meetings being in Scotland. The detailed work is handled by a number of Com¬ mittees. As I have already said, the Conservancy lays the greatest stress on the scientific value of nature conservation, in contrast to the “amenity bodies”, though it is difficult, or impossible, to THE CHANGING f CORA OF BRITAIN 190 keep the two interests strictly separate. When I am reporting on the merits of a proposed nature reserve, after describing the scientific importance of its flora and fauna, I often find it hard to resist bringing in the scenic beauty of the landscape or the attractiveness of the vegetation, though my allusions to these tend to take on an almost apologetic tone. It is as if I were trying to say “And of course the place really is beautiful as well, though perhaps I ought not to mention the fact”. As no doubt you all know, the central immediate object of the Conservancy is to establish a number of National Nature Reserves chosen as sites of geological or physiographical impor¬ tance, or as representing leading types of vegetation or assem¬ blages of interesting plants or animals. The sites are either bought outright by the Conservancy (which is not allowed to give more than a sum fixed by the District Valuer as the proper price of the land), or a “Management Agreement” is made with the owner or occupier intended to ensure that the site is man¬ aged in accordance with the Conservancy’s objects. Probably it is unnecessary with my present audience to explain why active management is necessary in the great majority of reserves. The original list of proposed reserves was between 70 and 80 in England and Wales excluding those of purely geological in¬ terest and an original list of 24 in Scotland, but these have been considerably altered. Some originally proposed reserves have proved impossible to secure or no longer worth securing. Other highly desirable areas have come to the notice of the Conser¬ vancy since the original list was made. So far as can be foreseen at present the total number of National Nature Reserves in Eng¬ land and Wales is unlikely to reach 100. Of those now on our list, including Scotland, 6 are ready for “declaration”, on making which the Conservancy takes over responsibility for the area. With one which has been already declared, these make the Con¬ servancy’s total holdings to date 21,615 acres, an acreage mainly accounted for by two large reserves of about 10,000 acres each. Some 3 or 4 more are in an advanced stage of negotiation, and 10 others are under negotiation. Only one, the Beinn Eighe reserve in Wester Ross, has been actually declared. This is a fine tract of 10,450 acres of mountain and moorland with some remains of old self-regenerating native pine forest. The Con¬ servancy have abstained from making “declarations” until ar¬ rangements have been completed to take over effective responsi¬ bility in each case. But additional declarations are expected soon.1 This may seem to some of you rather a poor result of 3 years’ work, but actual experience shows how difficult and time-con¬ suming are the negotiations for acquisition or management. iThe figures given in this paragraph relate to the end of 1951. At present (March 1953) 9 Reserves have been declared (7 in England and 2 in Scotland), two have been acquired but not yet declared, and 20 more are being negotiated. THE CONSERVATION O F BRITISH VEGETATION AND Sl’EClES 191 Several National Nature Reserves on the Conservancy’s list belong to the National Trust, and these are already managed by local committees under the Trust. Good examples are Wicken Fen and Blakeney Point. The Wicken Fen committee, which consists largely of Cambridge biologists, does its scientific job very well, and it seems unlikely that the Conservancy will ever want to interfere with their work. In regard to certain other National Trust reserves management agreements with the Trust will be arranged, by lease or otherwise, ultimate ownership naturally remaining in the hands of the Trust. Since the different reserves are so various in size and nature the problem of management will be different in each, but a scien¬ tific officer of the Conservancy, in some cases resident on or near the reserve, will have to be responsible for each. It is intended to make a thorough survey and study of the animal and plant populations included in the reserves, but in most cases of course this will be the work of many years. Several preliminary sur¬ veys have already been made. In some reserves experimental work will be carried on, but care will be taken not to interfere with the general character of the reserve. The 10,000 acre tract of peat moorland in Westmorland, known as the Moorhouse re¬ serve, has been acquired mainly for the purpose of large-scale experiments, which have already been initiated. In contrast with the Beinn Eighe and Moorhouse reserves, many of the National Nature Reserves are of quite small areas, so that in tota lthey can make but a tiny contribution towards preserving the natural vegetation of the country. This was fore¬ seen by the two committees of the Ministry of Town and Country Planning which sat from 1945 till 1947 and made recommendations for the establishment of National Parks and for the Conservation of Wild Life. Accordingly their reports recommended the de¬ signation of large “Conservation Areas”, characteristically beau¬ tiful tracts of country bearing important vegetation in which care should be taken not to alter the character of the landscape except under the most pressing national necessity, but at the same time not subjecting them to the stricter regime of the National Parks and particularly of the National Nature Reserves. Largely through misapprehension of the aims in view, the institu¬ tion of Conservation Areas was rather widely opposed, and the Government refused to accept it. This failure involved a serious loss to the chances of preserving the character, depending largely on the vegetation, of some of the most beautiful parts of Britain outside the areas of the National Parks. The Government did however allow the insertion in the National Parks and Access to the Countryside Bill (1949) of clauses that go some little way towards securing the ends in view, both the aims of the Nature Conservancy and those of the National Parks Commission. Thus Section 23 of the Act reads “Where the Nature Conser¬ vancy are of opinion that any area of land, not being land for the time being managed as a nature reserve, is of special interest 192 THE CHANGING FLORA OF BRITAIN by reason of its flora, fauna, or geographical or physiographical features, it shall be the duty of the Conservancy to notify that fact to the local planning authority in whose area the land is situated”. And in Section 87 of the Act we find “The Commis¬ sion [i.e. the National Parks Commission] may, by order made as respects any area in England or Wales, not being in a National Park, which appears to them to be of such outstanding natural beauty that it is desirable that the provisions of this Act relating to such areas should apply thereto, designate the area for the purposes of this Act as an area of outstanding natural beauty . . Following paragraphs of the Act provide for full reference of such proposed orders of designation to the local authorities con¬ cerned and for adequate publication in newspapers of the pro¬ posals to make them. The Commission are enjoined to consider representations made to them as to the effect of a proposed order, while the Minister to whom the proposed order must be submitted may of course refuse to confirm it or may only con¬ firm it with modifications. Thus, while the Act lays on the Conservancy the duty of notifying local planning authorities of areas considered to be of special scientific interest, but gives them no further powers in regard to such areas, the National Parks Commission may make orders in respect of areas of outstanding natural beauty, but before they can come into force, the orders have to run the gaunt¬ let of local criticism and to face the possibility of the Minister refusing to confirm them. It is thus clear that a real power of preventing any kind of nature conservation, outside the National Parks and the National Nature Reserves, lies with local opinion and with the Minister. How far local opinion can be influenced in favour of conservation, when it threatens or is thought to threaten local interests, remains to be seen. * It is of course true that areas of “outstanding natural beauty” and those of “special scientific interest” do not always coincide, but they very often do', just because they are both likely to be areas of unspoiled wild or semi-wild country, which are both beautiful and also harbour interesting native plants and animals. It is clearly desirable for the Commission and the Conservancy to work together in such cases. A great deal of the time of the scientific officers of the Conservancy has been occupied with designating Section 23 areas during the last two years. We now come to the actual ways in which the work of the Nature Conservancy may help botanical and ecological interests. So far as plants are concerned there are two particular objects that may be pursued in making nature reserves — first, good and sufficient representation of the distinct types of natural or semi- natural vegetation existing in the country, and secondly, the con¬ servation of areas which contain a number of specially interest¬ ing or relatively uncommon species. Both are important and the policy of the Conservancy is to pursue both : in certain cases THE CONSERVATION OE BRITISH VEGETATION AND SPECIES 193 the two objects may be fulfilled in a single reserve. The opinion of the Conservancy is rather against making a reserve to pre¬ serve a single species, however rare, and a practical objection of course is that the making of such a reserve calls general attention to the existence of the rare species in that place, with the risk of its being over-collected or even exterminated by greedy collec¬ tors. It would be interesting and useful to hear the views of experienced field botanists on these matters, and especially as to what if anything can be done to safeguard the localities of very rare species. Besides scientific work in the reserves, which will be carried out not only by Conservancy scientific officers but also, it is ex¬ pected, by other qualified scientists such as research workers from the universities, the Conservancy has other duties. In the words of its Charter, its functions shall not only be “to establish, maintain and manage nature reserves in Great Britain, including the maintenance of physical features of scientific interest, and to organise and develop the research and scientific services re¬ lated thereto”, but also “to provide scientific advice on the con¬ servation and control of the natural flora and fauna of Great Britain”. This function has been carried out as opportunity offered, in response to requests from Government Departments and others, and also on the initiative of the Conservancy. It is expected to increase considerably in volume as the Conservancy becomes better known and gradually acquires greater knowledge and experience. Among various topics that have thus occupied its attention, the effects on plants and animals of the spraying with weed-killer of grass verges on roadsides, which has been undertaken by certain local authorities, is now being studied by qualified Conservancy agents. Another important activity is the provision of grants for suitably qualified people — both training grants for students who are working under approved directors and maintenance grants for research workers engaged on approved investigations, mainly of ecological or some ancillary nature. All this entails a great many interviews with candidates for grants, many enquiries and much correspondence. The Conservancy contemplates the establishment of two research institutes, one in the north and the other in the south of England. Neither of these is yet at work, but suitable pre¬ mises have been or are being acquired.2 It is probable, however, that progress with at least one of them will have to be deferred owing to the current urgent need for economy. The originally expected Treasury grant for next year has been cut, though not to such an extent as to cripple the general work of the Conser¬ vancy. Simple laboratory accommodation has been provided at 2The northern research institute, “Merlewood”, near Grange-over-Sands, will begin work in the summer of 1953. M THE CHANGING FLORA OF BRITAIN 194 the London and Edinburgh offices of the Conservancy, and there is a library and a collection of maps at each. To give you some idea of the size and structure of the Con¬ servancy Headquarters organisation, without of course going into details, I may mention that in November 1951 besides the Director-General and the Secretary of the Conservancy there were based on the London headquarters : — 2 Administrative Officers, a Land Agent, an Accountant, 6 Office and Technical Assistants, and 9 Scientific Officers of various grades, besides Personal Assistants, Clerical staff, typists, etc." At the Edinburgh headquarters, besides the Director for Scot¬ land, an Administrative Officer and 6 Office and Technical Assis¬ tants, there were in 1951 4 Scientific Officers based on Edinburgh. The Scientific Officers spend, of course, a great part of their time in the field. Up to now they have been mainly engaged in preliminary work such as broad surveys of proposed reserves and areas of “special scientific importance” (Section 23 of the Act), reporting on possibly desirable new reserves, etc. In much of this work they have been generously and substantially helped by biologists who are not officers of the Conservancy. In the future, we look forward to stationing a number of scientific officers in the country, which will be divided into regions with a Regional Officer in general charge of each, while others will be responsible for individual reserves, or groups of reserves. These latter, some¬ times called ‘wardens’ (a term the Director-General disliked — “resident scientific officers” is preferred) will be responsible not only for the management of single reserves or groups of reserves but for study of, and research into, the plant and animal popula¬ tions, whether done by themselves or by visiting scientists from the universities or elsewhere. Other scientific officers, specialists in various lines of work, will be available for visits to any place where their services are required. From all this you will have gathered that the Conservancy is still in a very early stage of development. Nothing but prelimin¬ ary work has yet been done, and that is not by any means finished. One serious lack that has hampered much of the Con¬ servancy’s early work has been the great difficulty of getting well qualified senior scientific officers, men (or women), for in¬ stance, of the status and experience of lecturers or readers at universities. There are not too many of them in the country with sufficient knowledge of our sphere of work, and those that do exist and have the necessary ecological knowledge and outlook almost invariably, and quite understandably, refuse to abandon aThe staff has since been considerably augmented. THE CONSERVATION OF RRITISH VEGETATION AND SPECIES 195 an academic career or to give up their specialised researches, however deeply they may sympathise with the work which the Conservancy is trying to do. A particular hindrance has been the lack of a Deputy Director-General, for which post we have been quite unable to find a suitably qualified person who was willing to take it. This lack has deprived the Director-General of essential help and grievously overburdened him with detailed work. As a result of the dearth of senior scientific officers, our recruitment has had perforce to be almost confined to people, many of whom, though often highly talented, have not yet gained the knowledge and practical experience of our flora or fauna required for the training of young and untrained recruits who have just graduated, a necessary function of senior officers. That trouble however should be cured with time. In an organisation embarked on a completely new kind of task teething troubles can only be expected, and we must look forward to growing pains for some years to come. Besides the hindrances to adequate internal organisation which I have in¬ dicated, we are of course faced by the severest competition for the use of land, from the armed services for training grounds, air fields and bombing ranges, from the Forestry Commission for new7 planting, from the greatly increased quarrying of limestone and gravel digging, and now from the further intensification of pres¬ sure for fresh ploughing to produce more food. We are often re¬ proached for wanting to “sterilise” land, since the fruitfulness of biological and ecological knowledge is beyond the ken of too many “practical men”. Of course we have to give way to overriding national needs such as the demands of defence and food produc¬ tion, but we should certainly appreciate a better and wider under¬ standing of what we are trying to do and why we are trying to do it. In the discussion which followed this paper: — Canon Haven said that it was clear that the Society should continue to place conservation very much in the forefront of its activities. The npathy shown by the public when biological interests are threatened is still far too great. He thought that two matters mentioned by Sir Arthur Tansley should be of special interest to us. The first was the difficult question of how rare species can best he preserved. The alter¬ native policies seemed to be either to notify the precise localities to a national body who would make arrangements for them to be guarded, or to rely on secrecy so that a rigid taboo should be imposed on anyone men¬ tioning the localities where they grow. This was a matter with which our own Society should he very much concerned. The second matter, of special interest to us, was the project for setting up research insti¬ tutes. It was understandable that more experienced workers hesitated to give up their present careers to undertake this sort of work and that there was a dearth of available recruits. But it was clear that there was something of a swing over to botanical studies among young 196 THE CHANGING FLOBA OF BRITAIN people interested in natural history. We should do all we can to en¬ courage them to take up work of the kind undertaken by the Nature Conservancy and to make known the opportunities of applying for posts in their service. Mr. Lousley said that the Society was already doing a great deal of work towards the conservation of the British flora — which was one of our objects set out in the Rules. Some 40 “ threats ” were reported by members during 1951 and in all cases we had taken such action as was open to us. Unfortunately much of this work must remain un¬ publicised for reasons which are obvious, but it cannot be too widely known that we are keenly and actively interested and that we have for some years had a special Committee appointed to deal with conserva¬ tion. In the case of the more important threats we work in close colla¬ boration with the Nature Conservancy. Members of our Conservation Committee meet representatives of the Nature Conservancy at inter¬ vals of six months at a joint meeting when matters of common interest are discussed. He hoped that Sir Arthur Tansley’s remarks would lead to even closer collaboration between the Society and the Conservancy than before. Sir Arthur Tansley replied to the effect that the Society’s help in dealing with the problem of the conservation of rare species would be particularly valuable. The Conservancy was faced with great diffi¬ culties in knowing how best to deal with localities where rare plants were known to occur (such as Cwm Idwal) or with very scarce species (such as Cypripedium Calceolus L. and C ephalanthera rubra (L.) Rich.) limited to localities which were kept secret. It was very difficult to know what policy should be adopted. CONCLUDING REMARKS BY THE PRESIDENT 197 CONCLUDING REMARKS BY THE PRESIDENT Canon Raven, in his concluding remarks, said that this had been a very memorable Conference. It was memorable for the extraordinarily high level of interest and ability displayed in the papers which had been read and also in the way in which the whole subject had hung together and moved forward in a de¬ finite rhythm. The value and quality of the Conference laid a measure of responsibility on all those who attended. A great many suggestions had been made by various speakers and he thought it would be extremely valuable if out of these the Society could initiate a country-wide detailed study if this could be done collectively. We should try to develop a limited number of projects rather than to dissipate our resources. As a first step a list should be made of the work which needs to be done. From this list two or three suggestions might be selected for collective work and the support of members invited. It was a reproach that insufficient use had been made in the past of the very wide knowledge available from the Society as a body. The Conference had opened up a great vision of what the Society might do, and it had drawn attention to certain aspects of field botany which were not apparent before. We must see that these opportunities were not neglected. 198 TJTF CHANGING FLORA OF BRITAIN FIELD MEETING TO THE NEIGHBOURHOOD OF ASHFORD, KENT On Sunday, April 6th, a whole day field meeting was arranged with a view to demonstrating some of the species mentioned in papers read to the Conference. Under the leadership of Mr. J. E. Lousley and Mr. D. McClintock, 90 members and friends travelled in two coaches and private cars to Hothfield, near Ashford, Kent. Shortly before reaching Swanlej^ the coaches passed sandv fields where “shoddy’' is used as a manure (cf. p. 160) and 22 species of wool aliens have been collected ( London Naturalist, 28, 27, 1949). The party stopped at the southern end of Mereworth Woods to examine a large colony of Acaena anserinifolia (Forst.) Dr. which grows here abundantly in competition with native plants (see p. 152). Fruiting heads were collected and the long barbed spines examined. At Ripper’s Cross near Hothfield, Thlaspi alliaceum L. was seen in abundance in the locality where it was first found in Ma}- 1923 (see p. 148, and J. Min. Agric., 30, 535-8, 1923 ; Rep. Bot. Soc. cfr E.C., 7, 28-29, 1924; J.Bot., 62, 306-7, 1924). In spite of the heavy snow which fell about a week before the meeting, the plants were in full flower, and a few had formed seed-pods (Plate VI). Although the party scattered and examined many fields, no ap¬ preciable extension of the known range was reported. The plant was found in two fields on the west side of Bear’s Lane in arable and hedgerows, and in much smaller quantity in two fields on the east side of the lane and in Bear’s Lane Wood. The greatest distance between the plants observed was 450 yards. Later in the afternoon the coaches proceeded to Boxley War- em, near Maidstone. Here Buxus sempervirens L. was formerly abundant, for John Ray, in 1695, wrote “. . . I find in the notes of my learned friend Mr. John Aubrey that at Boxley (in Kent) there be woods of them” (Ray in Camden, Britannia, 262). In recent times the Box here has not been abundant and much of the remaining colony was destroyed during the war. It grows on very steep chalky slopes in a habitat similar to the one at Box Hill (cf. p. 187), and the village is apparently named after it. Unfortunately only a few of the party were successful in finding the remaining trees in the short, time available. Beneath some of the ancient trees of Taxus baccata L., plants of Euphorbia Lathyris L. were seen in a locality far from houses, which has been known since 1862. Dr. Warburg’s remarks of the previous day were recalled when several old trees of Quercus Ilex L. were found amongst characteristic native trees and shrubs of the chalk, and in places where they were very un¬ likely to have been planted. Prof. Tutin found a seedling and thus confirmed that the Quercus was regenerating. PLATE VI Thl (t sp i nllinreum L. at Ripper's Cross, Hoi Ti field, Kent. FIELD MEETING TO THE NEIGHBOURHOOD OE ASHEORD, KENT 199 On the return journey the coaches passed Forstal Quay, and crossed the Medway at Aylesford where Scirpus tri- queter L. was formerly plentiful. The colony seen by J. E. Lousley in 1934 was destroyed by dredging shortly afterwards and the species now appears to be extinct here. Mention of an extinction as the last example of the Conference was a fitting reminder of the importance and urgency of conservation. The loss of some species is inevitable owing to “improvements” of economic importance which botanists cannot hope to resist. To save others, where it is possible to take effective action, is a mat¬ ter of the greatest importance. Additions to “The Changing Flora of Britain” can take their course: it is the duty of every¬ one interested to help in the work of keeping our losses as low as possible. ‘200 THE CHANGING FLORA OF BRITAIN INDEX Figures in heavy type refer to pages on or opposite which figures and Plates appear. A bleu alba, 47 Acaena anserinifolia, 143, 151, 152, 156-7, 160, 198 Acer Pseudo-platanus, 48, 74, 171, 173-4 Adonis annua, 133-4 Aegopodium Podagraria, 26-7, 29 Agamospermy, 21 Agrimonia odorata, 47 Agropyron Donianuin, 49; ylaucum, 48; repens, 57 Agrostemrna Githugo, 133, 156 Alchemilla alpina, 90; filicaulis, 90; glomerulans, 90: vulgaris, 47; Wichurae, 89. Aliens, invasion by, 15— *; 22, 140— > Allsma gramineum, 22-3 Alnus glutinosa, 48; Incana, 48, 173 Alopecurus alpinus, 97 Alpine plants in Scandinavia, 77— > Amaranthus Bouchoni, 47; retro- plexus, 47 Amelanchier laevis, 172, 175 Andreas, Dr. Ch. H., 84 Anemone llepatica, 47 Anser albifrons flavicornls, 114 Antennaria dioica, 46 Anthrlscus sylvestris, 26, 32, 39 Anthyllis Vulnerarla, 92 Apomixis, 16, 21, 99 Arabis petraea, 50 Arable land, weeds of, 130—* Arbutus Vnedo, 107-8, 116, 117, 118, 121, 129 Arctostaphylos alpinus, 83; Uva- ursi, 84, 86 Arenaria biflora, 68; ciliata, 89, 90, 92, 95; gothica, 90, 95; humlfusa, 92; norvegica, 89, 90 , 93 , 96, 101 Arenostola brevilinia, 15 Armeria marltima, 73, 76 Ash, G. M., 168 Ashford, field meeting, 198— * Astragalus danicus, 125, 127, 129, 177 Bedfordshire, wool aliens, 160— > Belula callosa, 94; nana, 64 , 67-8 , 70, 75, 83-5, 87; pendula, 70; pubes- cens, 64, 70, 75 Bldens bipinnata, 161 Botrychium Lunaria, 46 P, ox-tree, native of England, 184—* Brachypodlum pinnatum, 149 Bradshaw, A. D., 181 British Flora, recent additions, 49—*; 140 — * Bromus erectus, 47; secallnus, 16 Buddleja Davidll, 121, 174; =varia- bilis, 48 Bunlas orientalls, 146, 149, 152 Bunion Bulb ocas tanum, 46 Bupleurum rotundifolium, 134 Burton, Dr. M., 52 Buxus sempervirens, 125, 184—*, 185, 186, 198 Calamagrostis scotica, 97 Calluna vulgaris, 71, 124, 156 Campanula persicifolia, 47; rotundi- folia, 92; uniflora, 93, 112 Cannabis sativa, 143 Cardarnlnopsis petraea, 96 Cardaria Draba, 134, 136, 146 Car ex acuta, 85; aguatllis, 85 , 86, 87-8; arctogena, 93; caryophyllea, 21; Crawfordii, 143; demlssa, 21; dioica, 47; flava, 16, 21; gracilis, 86; Grahami, 89; holostoma, 92; Hostiana, ill, 112; humilis, 125; lepidocarpa, 21; limosa, 23, 84; rarifiora, 90; recta, 89; rigida, 87; saxatilis, 90; vulpinoidea, 143, 146 Carum Carvi, 145 Castanea sativa, 171, 174 Caucalis daucoides, 47 Centaurea Cyanus, 130; solstiti- alis, 142 Cephaloziella Baumgartneri, 47 Cerastium. alpinurn 90; brachypeta- lurn, 51; Edmonstonii, 89, 95; tet- randrum, 138 Chaerophyllum temulentum, - tem- ulum, 26— > Chamaenerion angustijolium, 14, 24, 137-8 Change due to natural factors, 19—*; to human factors, 26-*; shown by weeds, 130—*; trees and shrubs, 171 — * Changing flora. 14, 19, 26, 46, 52 Chenopodium album, 47, 161; fici- folium, 47; glaucum, 47; rubrum, 47; striatum, 47 Chrysanthemum segetum, 133 Chrysosplenium oppositifolium, 116, 166 Cinclidotus fontinaloides, 47; ripa- rius, 47 Clrsium heterophyllum, 49 Clapham, A. R., 26 Classification of aliens, 154-6 Claytonia alslnoides, 131, 132. 134; perfoliata, 134, 136 Cochlearia danica, 138 Commercial factors, 147 Conservation, 188— > Continental Element, 124—* Conway Valley. 40—* Coriandrum sativum, 143 INDEX 201 Cornus suecica, 84, 85 Coronilla varia, 48 Coronopus didymus, 134 Corylus Avellana. 156 Cotoneastcr frigida, 175; microphyl- la, 173-5, 179; Simonsii, 172 Council for Preservation of Rural England, 189— *■ Crataegus, hybridisation, 181— > Crataegus monogyna, 181-2; oxya- canthoides, 181-2 Crepis taraxacifolia, 24 Cynodon Dactylon, 153 Cyperus fuscus, 23 Cystopteris fragilis, 46 Daboecia cantabrica, 119 Dactylis Aschersoniana, 145 Dahl, Eilif, 77 Damasonium AVtsma, 69 Daphne Laureola, 47; Mezereum, 47 Davey, Miss A. J., 164 Delia segetalis, 46 Delphinium consolida, 134 Dentaria pinnata, 47 Deschampsia alpina, 96, 99, 100; caes- pitosa, 99, 100 Dianthus gratia nopolitanus, 125 Diapensia lapponica, 49, 50, 73, 83, 90 Dony, J. G., 160 Draba cacuminum, 93; norvegica, 89 Dryas octopetala, 82 , 83, 87, 90 , 95 Dulichium spathaceum, 113 Early records, 14 Elephas primigenius, 61 Elodea canadensis, 110, 137 Empetrum hermaphroditum, 101; nigrum, 64, 71, 101 Epilobium, key, 169 Epilobium adenocaulon, 140, 168— s*; nummularifolium, 164; peduncu- lare, 15, 110, 131, 140, 148, 156, 164 — 165 Equiformal areas, 113 Equisetum ramosissimum, 50-1: syl- vaticum, 47 Eragrostis minor, 48 Erica ciliaris, 116, 119,- cinerea, 124; Machaiana, 116, 120; meditei'ra- nea, 116; tetralix, 71, 116, 124 Erigeron borealis, 89: canadensis, 134, 136. 137 Eriocaulon septangulare, 96, 105, 111, 113 Eriophorum brachyantherum , 90: latifolium, 40~> Erodium cicutarium. 129, 153; mos- chatum, 143 Erucastrum gallicum, 48 Eiuyngium campestre, 14 Established species, 148 Euphorbia Esula, 48: hyberna, 116; Peplis, 106, 120 Euphrasia frigida, 89: Heslop-Harri- sonii, 96; lapponica, 93; scotica, 89 Exaculum pusillurn, 96 Festuca heterophylla, 145; ovina, 92, 100; rubra, 99, 100; vivipara, 89, 99, 100 Field Meeting at Ashford, 198-> Filipendula vulgaris, 47 Fissidens crassipes, 47 Fuchsia magellanica, 172 Galeopsis Tetrahit, 15, 71 Galinsoga ciliata, 139; parviflora, 47, 132, 134-5, 138-9, 142 Galium glaucum, 47 Gaultheria Shallon , 173-4 Gentiana cruciata, 46, 68; pneumon- anthe, 47; verna, 95 Geranium pyrenaicum, 153 Glacial periods, vegetation in, 59->. Plants of late-Glacial, 75— 77. Lists of, 65-7. Table, 70. Relics, 84-> Gnaphalium supinum, 90 Godwin, H., 59 Goodyera repens, 47, 124, 177 Goose migration routes, 114 Guizotia abyssinica, 143. 156-7 Gunnera chilensis, 142 Gypsophila muralis, 46 Hedgerow species, 26-> Helianthemum canum, 20, 95, 179; Chamaecistus, 128, 177 Helxine Soleirolii, 142 Herminium monorchis, 46 Heslop-Harrison, J., 105 Heteromeyenia Iiyderi, 107, 114 Hieracium argenteum, 89; reticula - turn, 89; stictophyllum, 89 Hierochloe odor at a, 49 IJimantoglossum hircinum, 23 Hippopliae rhamnoides. 76, 94 Holosteum umbellatum , 69 Homogyne alpina, 49 Houttuynia cor data, 16 Human factors, 26— s-, 40— >, 181— > Hypochaeris maculata, 127, 129 Iberis arnara, 134 Impatiens fulva, 131, 134; parviflora, 134 Inula britannica, 23; hirta. 46: sali - cina, 126, 129 Jarninia muscorurn. 61 Jovet, Paul, 46 Juncus capitatus, 96; Dudleyi, 107; obt.uslflorus, 47: pallidus, 161; pygmaeus, 96: tenuis, 14, 47. 107, 131, 134: triglumis, 50 Junipeims communis, lio 202 THE CHANGING FLORA OF BRITAIN Kalanchoe Blossfeldiana, 100 Kalmia polifolia, 174 Koenigia islandica, 50, 90 Lactuca Scariola, 137-8; virosa, 137-8 Lamium album, 26 Larlx decidua, 172 Lathyrus latifolius, 47 Limonium humile, 123 Limosella aquatica, 46 Linaria minor, 146; repens, 48; vul¬ garis, 71 Linnaea borealis, 84, 85, 86, 124 Linosyris vulgaris, 124, 128 Linum praecursor, 68 Liparis Loeselii, 47, 126 Littorella uniflora, 46 Lloydia serotina, 95 Lobelia Dortmanna, 106 Loisleuria procumbens, 90 Lolium temulentum, 47, 133 Lousley, J. E., 140 Lupinus noothatensis, 142, 148 Lusifanian elements, 105-> Luzula arctuata, 90; luzuloides, 145; Parviflora, 93 Lycopodium clavatum, 48, 76; Selago, 46 Mahonia Aquifolium, 173 Maianthemurn bifolium, 143 Matricaria inodora, 135; matricari- Oides, 48, 134-5, 138 Medicago hispida, 143; minima, 153 Meikle, R. D., 49 Melandrium album, 20; rubrum, 20 Melderis, A., 89 Mentha longifolia, 156 Milium scabrum, 49 Mimulus guttatus, 131 Minuartia rubella, 90; stricta, 95 Moneses uniflora, 124 Monotropa hypophegea, 47 Mountain floras compared, 89— > Mutation, 101 Myosotis alpestris, 95; brevifolia, 95 Myosurus minimus, 46 Myricaria gcrmanica, 94 Myriophyllurn alter niflorum, 69, 105-6 Myrrhis odorata, 156 Naias ft.exilis, 69, 105, 107 Nasturtium microphyllum, 49 National Parks Commission, 189— > Natural factors, 19 Naturalised species, 148 Nature Conservancy, 188— > Nature Reserves, 191— > Netherlands, glacial relics, 84— > North American elements, 105-> Ophrys apifera, 110 Orchis cruenta, 49; Francis-Drucei, 98; Fuchsii, 96; purpurea, 124; purpurella, 89; traunsteineri, 49 Osmunda regalis, 47 O tan thus maritima, 120 Oxalis corniculata, 14 Oxycoccus macrocarpus, 159 Oxyria digyna, 96 Panicum miliaceum, 143 Papaver alpinum, 68; Argemone, 131, 134; Laestadianum, 93; lapponi- cum, 93; relictum, 93; Rhoeas, 156 Pedicularis flammea, 112; hirsuta, 68 Phalaris canariensis, 143, 156 Phleurn arenarium, 46 Phoenix dactylifera, 173 Phormium Colensoi, 142; tenax, 142 Pigott, C. D., 184 Pinguicula grandiflora, 107; lusita- nica, 106 Pinus mugo, 173; nigra, 173; sylves- tris, 47, 124, 171, 174, 177 Planorbis arcticus, 61 Poa alpina, 95, 99, 100; annua, 15; arctica, 92, 93, 99, 100; Chaixii, 145; flexuosa, 77, 78, 89, 93; glau- ca, 90, 95; lierjedalica, 99, 100; jemtlandica, 89, 99, 100; praten- sis, 90, 99 Polemocliors, 146 Polemonium coeruleum, 68, 127 Polygala vulgaris, 95 Polygonum viviparum, 96, 99 Polyploidy, 21, 99, 101 Populus canescens, 175; nigra, 175; tremula, 70 Potamogeton epihydrus, 49, 96, 105-6, 111; polygonifolius. 111, 112; suecicus, 95 Potentilla Chamissonis, 92; Crantzii, 90; fruticosa, 69, 95, 124, 127; nivalis, 68; nivea, 68 Poterium muricatum, 47 Primula elatior, 19, 126; farinosa, 101; scotica, 97, 101; veris, 19; vulgans, 19, 116, 124 Prunus cerasifera, 172; Cerasus, 172; domestica, 172; Padus, 48 Pseudotsuga taxifolia, 172 Pulsatilla vulgaris, 46 Qualitative and quantitative change, 19, 23 Quercus Cerris, 171, 174; lanuginosa, 46 Questier, Abbe, 46— > Ranunculus aconitifolius, 68; hyper- boreus, 68, 83; lingua, 69; muri- catus, 148. 152, 156; nemorosus, 68; ophioglossifolius, 24; Ques- tieri, 46 Rapistrum hispanicum, 156; rugo- SUm, 149, 152, 157 Raven, Rev. Canon C. E., 14, 197 INDEX *203 Rhinanthus Lintonii, 97, 98; loclia - brensls, 97, 98 Rhinoceros antiquitatis, 61 Rhododendron lapponicum , 93, 112; ponticum, 171, 173-5 Ricinus communis, 156 Robinia pseudo-acacia, 48 Roegneria Doniana, 97 Rubia peregrina, 117, 118 Rub us saxatiUs, 84 Rumex alpinus, 142, 145; crispus, 153; cuneifolius, 144, 145, 148, 156; obtusifolius, 153 Sagina intermedia, 90; procumbens, 164 Salisbury, Sir E., 130— > Salix arbuscula, 67; lierbacea, 64 , 67, 75, 80, 83-4, 90; lapponica, 67; polaris, 68, 84; pliylicifolia, 64; reticulata, 81, 84, 87, 90 Salsola pestifera, 145 Salvia verticillata, 48 Saxifraga caespitosa, 90, 91; cernua, 99; hieraciifolia, 93; oppositifolia, 83; nvularis, 90; stellaris, 90 Scandinavia, alpine plants, 77— >; mountain floras, 89— »- Scheuchzeria iialustris, 23, 49, S4 Schoenus nigncans, 47 Scirpus triqueter, 199 Scutellaria hastifolia, 22, 143 Seduin Rosea, 77, 79 Seed dispersal, 109 Selinum Carvifolia, 126 Senecio campestris, 126; integrifolius, 126-7, 129; paludosus, 21-2; spathu- lifolius, 47, 95, 126; squalidus, 14, 49, 134, 137-8, 140, 148, 156; VISCO- SUS, 39, 48, 134. 137, 146 Setaria viridis, 143 • Shoddy, 160— > Sibthorpia europaea, 106-7 Silene acaulis, 83 , 96; anglica, 134; coelata, 68 Simethis planifolia, 107 Sisyrinchium angustifolium, ill, 107, 115 Society for Promotion of Nature Reserves, 189— >- Solanum nigrum, 153, 161; sara- choides, 143, 146 Solidago glabra, 48; Virgaurea, 48, 92 Sorbus anglica, 178- 179; Aria, 175, 177, 178; Aucuparia, 178; austri- aca, 179; bristoliensis, 179; hiber- nica, 178; intermedia, 172; mini¬ ma, 179; Mougeotii, 179; rupicola, 178; subsimilis, 179; torminalis, 178 Southbya nigrella, 47 Spartina alterniflora, 15, 21; mari- tima, 21; Townsendii, 15, 21 Specularis liybrida, 134 Sphyraclium columella, 61 Spiranthes Romanzoffiana, 96, 105, 111, 113, 114 Stachys alpina, 73 Status, comparison of, 155 Stellaria crassipes, 92 Subularia aquatica, 68 Sioertia perennis, 47 Tagetes minuta, 161 Tanacetum vulgare, 26, 34 Tansley, Sir A., 188-> Taraxacum tornense, 93 Teesdalia nudicaulis, 125, 129 Tetragonolobus maritimus, 148, 150, 153, 156; siliquosus, 150 Thalictrum alpinum, 67; minus, 46, 95 Tlilaspi alliaceum, 148, 152, 156, 198; Calaminare, 96 Thuja plicata, 172 Thymus Drucei, 128 Tragopogon porrifolius, 142 Trapa natans, 113 Trees and shrubs, status, 171— > Trichophorum alpinum, 21 Trientalis europaea, 84, 85 Trifolium angustifolium, 161 Trollius europaeus, 92 Turdus e. ericetorum, 85 Tussilago Farfara, 26, 36 Tutin, T. G., 19 TJlmus carpinifolia, 180; coritana, 180; cornubiensis, 180; glabra, ISO; Plotii, 180; procera, 180 Unglaciated areas, 95 Unsuccessful introduction, 23 Vaccinium Myrtillus, 92 Valois, modifications in flora, 46— > Variability, changes due to, 15 Variation and Evolution in Plants, 16 Veronica agrestis, 137; filiformis, 131, 132, 138; fruticans, 90; persica, 47, 134-5, 137-8; spicata, 14, 20, 125-7, 129, 179; verna, 126 Vestigo parcedentata, 61 Vicia varia, 142 Viola rupestris, 95, 125 Viscaria alpina, 90 Vulpia megalura, 149, 152 Walker, D., 75 Walters, S. M., 124, 1S4 War aliens, 146 Warburg, E. I\, 171 Weeds, study of, 130— > West, R. G., 75 Wool aliens, l60-> Xantliium spinosum, 160 Zoologist’s approach, 52— > THE BOTANICAL SOCIETY OF THE BRITISH ISLES Membership is open to all persons, whether amateur or pro¬ fessional, interested in British botany. Societies, Libraries, Museums, Botanical Gardens and similar Institutions may be¬ come Subscribers. 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