Chapter XVI: Continental Islands of Recent Origin: Great Britain (2)

1. Limax marginatus, _var._ MACULATUS. Ireland; frequent, very
distinct.

2. ,, ,, ,, DECIPIENS. Ireland and England.

3. ,, flavus, _var._ SUFFUSUS. England; Melanic form.

4. ,, ,, ,, GRISEUS. England; Melanic form.

5. Agriolimax agrestis, _var._ NIGER. Yorkshire. Melanic. Azores.

6. ,, ,, ,, GRISEUS. England. Melanic.

7. Amalia gagates, _var._ RAVA. W. of England.

8. ,, sowerbyi, _var._ RUSTICA. England.

9. ,, ,, ,, NIGRESCENS. Surrey and Middlesex.

10. ,, ,, ,, BICOLOR. Ealing.

11. Hyalina crystallina, _var._ COMPLANATA. Near Bristol.

12. ,, fulva, _var._ ALDERI.

13. Vitrina pellucida, _var._ DEPRESSIUSCULA. S. England, Wales.

HELICIDAE.

14. Arion ater, _var._ ALBO-LATERALIS. England, Wales, Isle of Man;
very distinct.

15. ,, hortensis, _var._ FALLAX. England. Common at Boxhill.

16. GEOMALACUS MACULOSUS. Kerry and Cork. Three varieties have been
described, one of which occurs in Portugal.

17. Helix aspersa, _var._ LUTESCENS. England. Not rare perhaps in
France.

18. ,, nemoralis, _var._ HIBERNICA. Ireland.

19. ,, rufescens, _var._ MANCHESTERIENSIS. England.

20. ,, hispida, _var._ SUBGLOBOSA. England.

21. ,, ,, ,, DEPILATA. England.

22. ,, ,, ,, MINOR. England, Ireland.

23. ,, granulata, _var._ CORNEA. Lulworth, Dorset.

24. ,, virgata, _var._ SUBAPERTA. Bath.

25. ,, ,, ,, SUBGLOBOSA. England, Wales, Bantry Bay.

26. ,, ,, ,, CARINATA. Wareham, Dorset.

27. ,, caperata, _var._ MAJOR. England, Wales, Scotland. Distinct.

28. ,, ,, ,, NANA. England.

29. ,, ,, ,, SUBSCALARIS. Wales, Ireland.

30. ,, ,, ,, ALTERNATA. England, Kent.

31. ,, acuta, _var._ NIGRESCENS. England.

PUPIDAE.

32. Pupa anglica, _var._ PALLIDA. Not rare.

33. ,, lilljeborgi, _var._ BIDENTATA. Ireland.

{358} 34. ,, pygmea, _var._ PALLIDA. Dorset and Devon.

35. Clausilia rugosa, _var._ PARVULA. Ireland.

STENOGYRIDAE.

36. Cochlicopa lubrica, _var._ HYALINA. Wales, Scotland.

37. Coecilianella acicula, _var._ ANGLICA. England.

SUCCINEIDAE.

38. Succinea putris, _var._ SOLIDULA. Wiltshire.

39. ,, virescens, _var._ AUREA. Ireland.

40. ,, pfeifferi, ,, RUFESCENS. England, Ireland.

41. ,, ,, ,, MINOR. England.

LIMNAEIDAE.

42. Planorbis fontanus, _var._ MINOR. England.

43. ,, carinatus, ,, DISCIFORMIS. England.

44. ,, contortus, ,, EXCAVATUS. Ireland.

45. ,, ,, ,, MINOR.

46. Physa fontinalus, _var._ OBLONGA. England, Wales, Ireland.

47. LIMNAEA INVOLUTA. Ireland.

48. Limnaea glutinosa, _var._ MUCRONATA.

49. ,, peregra, _var._ BURNETTI. Scotland. Very distinct.

50. ,, ,, ,, LACUSTRIS. Perhaps in C. Verde Islands.

51. ,, ,, ,, MARITIMA. Great Britain.

52. ,, ,, ,, LINEATA. England.

53. ,, ,, ,, STAGNALIFORMIS. England.

54. ,, stagnalis, _var._ ELAGANTULA. Curious. In a pond at
Chislehurst.

55. ,, palustris, _var._ CONICA. England, Ireland.

56. ,, ,, ,, TINCTA. England, Wales.

57. ,, ,, ,, ALBIDA. England.

58. ,, truncatula, _var._ ELEGANS. England, Ireland. Distinct.

59. ,, ,, ,, FUSCA. Wales.

60. Ancylus lacustris, _var._ COMPRESSUS. England.

PALUDINIDAE.

61. Paludina vivipara, _var._ EFASCIATA. England. Not uncommon.

62. ,, ,, ,, ATROPURPUREA. Pontypool.

RISSOIDAE.

63. HYDROBIA JENKINSII. Thames Estuary.

64. ,, ventrosa, _var._ MINOR.

65. ,, ,, ,, DECOLLATA.

66. ,, ,, ,, OVATA.

67. ,, ,, ,, ELONGATA.

68. ,, ,, ,, PELLUCIDA.

CYRENIDAE.

69. Sphaerium corneum, _var._ COMPRESSUM.

70. ,, ,, ,, MINOR.

71. ,, ,, ,, STAGNICOLA.

72. ,, ovale, _var._ PALLIDUM. England.

73. ,, lacustre, _var._ ROTUNDUM. Wales.

74. Pisidium pusillum, _var._ GRANDIS.

75. ,, ,, ,, CIRCULARE. Wales.

76. ,, nitidum, _var._ GLOBOSUM.

{359} UNIONIDAE.

77. Unio tumidus, _var._ RICHENSIS. Regent's Park. Peculiar form.

78. ,, pictorum, _var._ LATIOR. England.

79. ,, ,, ,, COMPRESSUS. England.

80. ,, margaritifer, _var._ OLIVACEUS.

81. Anodonta cygnaea, _var._ INCRASSATA. England.

82. ,, ,, ,, PALLIDA. England, Ireland.

ESTUARINE OR MARINE PULMONOTRANCHS.

83. ASSIMINEA GRAYANA. Thames Estuary.

_Peculiarities of the British Flora._--Thinking it probable that there must also be some peculiar British plants, but not finding any enumeration of such in the _British Floras_ of Babington, Hooker, or Bentham, I applied to the greatest living authority on the distribution of British plants--the late Mr. H. C. Watson, who very kindly gave me the information I required, and I cannot do better than quote his words: "It may be stated pretty confidently that there is no 'species' (generally accepted among botanists as a good species) peculiar to the British Isles. True, during the past hundred years, nominally new species have been named and described on British specimens only, from time to time. But these have gradually come to be identified with species described elsewhere under other names--or they have been reduced in rank by succeeding botanists, and placed or replaced as varieties of more widely distributed species. In his _British Rubi_ Professor Babington includes as good species, some half-dozen which he has, apparently, not identified with any foreign species or variety. None of these are accepted as 'true species,' nor even as 'sub-species' in the _Students' Flora_, where the brambles are described by Baker, a botanist well acquainted with the plants of Britain. And as all these nominal species of Rubi are of late creation, they have truly never been subjected to real or critical tests as 'species.'"

In my first edition I was only able to name four species, sub-species, or varieties of flowering plants which were believed to be unknown on the continent. But much attention has of late years been paid to the critical examination of British plants in comparison with continental specimens, and I am now enabled to give a much more {360} extensive list of the species or forms which at present seem to be peculiar. For the following list I am primarily indebted to Mr. Arthur Bennett of Croydon. Sir Joseph Hooker has been so kind as to examine it carefully and to give me his conclusions on the relative value of the differences of the several forms, and Mr. Baker, of Kew, has also assisted with his extensive knowledge of British plants.

LIST OF SPECIES, SUB-SPECIES, AND VARIETIES OF FLOWERING PLANTS FOUND
IN GREAT BRITAIN OR IRELAND, BUT NOT AT PRESENT KNOWN IN CONTINENTAL
EUROPE. BY ARTHUR BENNETT, F.L.S. THE MOST DISTINCT AND BEST DETERMINED
FORMS ARE MARKED WITH AN ASTERISK.

1. *Caltha radicans (Forst.). "A much disputed species, or form of _C.
palustris_. It is a relatively rare plant." (J. D. H.) "Certainly
distinct from the Scandinavian form." (Ar. Bennett.)

2. *Arabis petraea (Lam.) _var._ grandifolia (Druce). Scotch mountains.
"The larger flowers alone distinguish this." (J. D. H.)

3. Arabis ciliata (R. Br.). In Nyman's _Conspectus Florae Europaeae_
this species is given as found in England and Ireland only. "A very
much disputed form of a plant of very wide distribution in Europe and
North America." (J. D. H.)

4. Brassica monensis (Huds.). "This and the continental _B.
cheiranthus_ (also found in Cornwall) are barely distinguishable from
one another." (J. D. H.)

5. Diplotaxis muralis (D. C.) _var._ Babingtonii (Syme). South of
England. "A biennial or perennial form; considered to be a denizen by
Watson." (J. D. H.)

6. *Helianthemum guttatum (Mill), _var._ Breweri (Planch). Anglesea.
"Very doubtful local plant. _H. guttatum_ (true) has lately been found
in the same locality." (J. D. H.)

7. *Polygala vulgaris (L.), _var._ grandiflora (Bab). Sligo, Ireland.
"A very distinct variety." (J. D. H.)

8. Viola lutea (Huds.), _var._ amoena (Symons). "_V. lutea_ itself is
considered to be a form of _V. tricolor_, and _V. amoena_ the better
coloured of the two forms of _V. lutea_." (J. D. H.)

9. *Cerastium arcticum (Lange), _var._ Edmonstonii (Beeby). Shetland
Is. "But _C. arcticum_ is referable to the very variable _C. alpinum_."
(J. D. H.) "Near to the European _C. latifolium_." (Ar. Bennett.)

10. *Geranium sanguineum (L.), _var._ Lancastriense (With.).
Lancashire. "A prostrate local form growing out of its native soil in
sand by the sea." (J. D. H.) Mr. Bennett writes: "I have grown _G.
sanguineum_ and its prostrate variety in sand, and neither became
Lancastriense."

11. Genista tinctoria (L.), _var._ humifusa (Dickson). Cornwall. "A
decumbent hairy form confined to the Lizard." (J. D. H.)

12. Cytisus scoparius (Link.), _var._ prostratus (Bailey). Cornwall. "A
prostrate form." (J. D. H.)

13. Anthyllis vulneraria (L.), _var._ ovata (Bab.). Shetland Is. "A
slight variety." (J. D. H.)

14. *Trifolium repens (L.), _var._ Townsendii (Bab.). Scilly Isles. "A
{361} well-marked form by its rose-purple flowers. Confined to the
Scilly Isles." (J. D. H.)

15. *Rosa involuta (Sm.), _var._ Wilsoni. (Borrer.) Wales. "There are a
multitude of forms or varieties of _R. involuta_, and _R. wilsoni_ is
one of the best-marked, found on the Menai Straits and Derry."
(J. D. H.)

16. Rosa involuta _var._ gracilis (Woods). "This is considered by many
as one of the commonest forms of _R. involuta_." (J. D. H.)

17. Rosa involuta _var._ Nicholsoni (Crepin). "Another slight variety
of _R. involuta_." (J. D. H.)

18. Rosa involuta _var._ Woodsiana (Groves). "A Wimbledon Common
variety of _R. villosa_." (J. D. H.)

19. Rosa involuta _var._ Grovesii (Baker). "Mr. Baker thinks this of no
account." (J. D. H.)

20. Rubus echinatus (Lind.). "A variety of the widely spread _R.
Radula_, itself a form of _R. fruticosus_." (J. D. H.)

21. *Rubus longithyrsiger (Lees). "Mr. Baker informs me that this is a
very distinct plant never yet found on the continent." (J. D. H.)

22. Pyrus aria (Sm.) _var._ rupicola (Syme). "A very local form,
confined to Gt. Britain, and owing its characters to its starved
position." (Baker.)

23. Callitriche obtusangula (Le Gall), _var._ Lachii (Warren).
Cheshire. "This is intermediate between two sub-species of _C. verna_."
(J. D. H.)

24. *Oenanthe fluviatilis (Coleman). South of England. "The fluitant
form of _AE. Phellandrium_." (J. D. H.)

25. Anthemis arvensis (L.), _var._ anglica (Spreng). N. Coast of
England. "A maritime form with more fleshy leaves formerly found near
Durham. It has other very trifling characters." (J. D. H.)

26. Arctium intermedium (Bab.). "There are two sub-species of _A.
lappa_, _majus_ and _minus_, each with varieties, and this is one of
the intermediates." (J. D. H.)

27. Hieracium holosericium (Backh.). Scotch Alps.

28. H. gracilentum (Backh.). ,,

29. H. lingulatum (Backh.). ,, A var. of this in
Scandinavia.

30. H. senescens (Backh.). ,,

31. H. chrysanthenum (Backh.). ,,

32. H. iricum (Fr.). Teesdale and Scotland.

33. H. gibsoni (Backh.). Yorkshire and Westmoreland.

34. Hieracium nitidum (Backh.). Lower glens of the Scotch Alps. Mr.
Bennett writes:--"The following Hieracia have been named by Mr. F. J.
Hanbury _as endemic forms_. One can only safely say they are certainly
not known in Scandinavia, as they have all been submitted to Dr.
Lindeberg. But usually Scotch species are not represented in Central
Europe to any great extent, though several do occur. Still these new
forms ought to be critically compared with all Dr. Peters' new
species."

35. H. Langewellense (Hanb.). Caithness.

36. H. pollinarium (Hanb.). Sutherland.

37. H. scoticum (Hanb.). Sutherland and Caithness.

38. H. Backhousei (Hanb.). Aberdeen, Banff, Inverness.

39. H. caledonicum (Hanb.). Caithness and Sutherland.

40. H. Farrense (Hanb.). Sutherland and Shetland Is.

41. H. proximum (Hanb.). Caithness. With regard to all these {362}
Hieracia Sir Joseph Hooker and Mr. Baker say:--"No case can be made of
these. They are local forms with the shadowest of shady characters."
Mr. Bennett writes: "H. iricum and H. Gibsoni are the best marked
forms."

42. *Campanula rotundifolia (L.), _var._ speciosa (A. G. More). W.
Ireland. "Very well distinguished by its large flowers and small calyx
lobes, approaching the Swiss C. Scheuzeri." (J. D. H.)

43. Statice reticulata (Sm.). "Baker agrees with me that this is also a
Mediterranean species." (J. D. H.)

44. Erythraea capitata (Willd.), _var._ sphaerocephala (Towns.). Isle
of Wight. "A form of _E. centaurium_ utterly anomalous in its genus in
the insertion of the stamens. A monster rather than a species."
(J. D. H.)

45. *Erythraea latifolia (Sm.). On the sandy dunes near Liverpool. "A
local form." (J. D. H.)

46. Myosotis collina (Hoffim.), _var._ Mittenii (Baker). Sussex.

47. Veronica officinalis (L.), _var._ hirsuta (Hopk.). Ayr, Scotland.

48. Veronica arvensis (L.), _var._ eximia (Towns.). Hampshire.

49. Mentha alopecuroides (Hull). Nearest to _M. dulcissima_ (Dum.).

50. Mentha pratensis (Sole). Only once found.

51. Chenopodium rubrum (L.), _var._ pseudobotryoides (H. C. Watson).

52. Salix ferruginea (Forbes). England, Scotland. "Probably a hybrid
between _S. viminalis_ and _S. cinerea_." (J. D. H.)

53. Salix Grahami (Borr.). Sutherland, Perth. "A hybrid?" (J. D. H.)

54. Salix Sadleri (Syme). Aberdeen. "A hybrid?" (J. D. H.)

55. *Spiranthes Romanzoviana (Cham.). Ireland (N. America).

56. *Sisyrinchium angustifolium (Mill.). Ireland. (Arctic and Temp. N.
America.)

57. Allium Babingtonii (Borrer). West England, West Ireland. "A form of
_A. ampeloprasum_, itself a naturalised species." (J. D. H.)

58. *POTAMOGETON LANCEOLATUS (Sm.). Anglesea, Cambridgeshire, Ireland.
Mr. Bennett writes:--"Endemic! I have taken a good amount of trouble to
ascertain this. Nearly 400 specimens I have distributed all over the
world with requests for information as to anything like it. The
response is everywhere the same, 'nothing.' The nearest to it occurs in
the Duchy of Lauenberg but is referable to _P. heterophyllus_."

59. Potamogeton Griffithii (Ar. Bennett). Carnarvon. "Nearest to this
is a probable hybrid from N. America, but not identical." (Ar.
Bennett.)

60. Potamogeton pusillus (L.), _sub-sp._ Sturrockii (Ar. Benn.). Perth.

61. Potamogeton pusillus (L.), _var._ rigidus (Ar. Benn.). Orkneys,
Shetlands.

62. Ruppia rostellata (Koch.), _var._ nana (Bosw.). Orkneys.

63. *Eriocaulon septangulare (With.). Hebrides, Ireland. N. America.

64. Scirpus uniglumis (Link), _var._ Watsoni (Bab.). Scotland, England.
"This is a variety of a sub-species of the common _S. palustris_."
(J. D. H.)

65. Luzula pilosa (Willd.), _var._ Borreri (Bromf).

66. *Carex involuta (Bab.). Cheshire. "A distinct enough plant but
probably a hybrid between _C. vesicaria_ and _C. ampullacea_, found in
one place only." (J. D. H.)

67. Carex glauca (Murr.), _var._ stictocarpa (Sm.). Scotland.

{363} 68. Carex precox (Jacq.), _var._ capitata (Ar. Benn.). Ireland.
"A remarkable plant (monstrosity?) simulating _C. capitata_ (L.)." (Ar.
Bennett.)

69. *Carex Grahami (Boott). "A mountain form of _C. vesicaria_."
(J. D. H.)

70. *Spartina Townsendi (Groves). Hampshire. "A distinct but very local
form of _S. stricta_, found in one place only." (J. D. H.)

71. Agrostis nigra (With.).

72. Deschampsia flexuosa (Trin.), _var._ Voirlichensis (J. C. Melvill).
Perth.

73. *Deyeuxia neglecta (Kunth), _var._ Hookeri (Syme). Ireland. "A
distinct variety confined to Lough Neagh." (J. D. H.)

74. Glyceria maritima (Willd.), _var._ riparia (Towns.). Hampshire.

75. Poa Balfouri (Bab.). Scotland. "An alpine sub-variety of a variety
of the protean _P. nemoralis_." (J. D. H.)

In his comments on this extensive list of supposed peculiar British plants, Sir Joseph Hooker arrives at the following conclusions:--

1. There are four unquestionably distinct species which do not occur in
continental Europe: viz.--

_One_ absolutely endemic species, POTAMOGETON LANCEOLATUS.

_Three_ American species, SISYRINCHIUM ANGUSTIFOLIUM, SPIRANTHES
ROMANZOVIANA, ERIOCAULON SEPTANGULARE.

2. There are sixteen endemic varieties of British species, viz.--

_Eleven_ of more or less variable species, Caltha palustris, _var._
RADICANS; Polygala vulgaris, _var._ GRANDIFLORA; Cerastium arcticum,
_var._ EDMONSTONII; Trifolium repens, _var._ TOWNSENDII; Rosa involuta,
_var._ WILSONI; Rubus fruticosus, _sub-sp._ LONGITHYRSIGER; Campanula
rotundifolia, _var._ SPECIOSA; Erythraea centaurium, _sub-sp._
LATIFOLIA; Carex involuta, (? Hyb.); Carex vesicaria, _var._ GRAHAMI;
Deyeuxia neglecta, _var._ HOOKERI.

_Five_ of comparatively well limited species. Arabis petraea, _var._
GRANDIFOLIA; Helianthemum guttatum, _var._ BREWERI; Geranium
sanguineum, _var._ LANCASTRIENSE; Oenanthe Phellandrium, _var._
FLUVIATILIS; Spartium stricta, _var._ TOWNSENDI.

The above twenty species are marked in the list with an asterisk. Of the remaining fifty-five, Sir Joseph Hooker says, "that for various reasons it would not be safe to rely on them as evidence. In most cases the varietal form is so very trifling a departure from the type that this may be safely set down to a local cause, and is probably not constant. In others the plant is doubtfully endemic; in still others a hybrid."

Even should it ultimately prove that of the whole number of the fifty-five doubtful forms none are established as peculiar British varieties, the number admitted after so {364} rigorous an examination is about what we should expect in comparison with the limited amount of speciality we have seen to exist in other groups. The three American species which inhabit the extreme west and north-west of the British Isles, but are not found on the continent of Europe are especially interesting, because they demonstrate the existence of some peculiar conditions such as would help to explain the presence of the other peculiar species. Whether we suppose these American forms to have migrated from America to Europe before the glacial epoch, or to be the remnants of a vegetation once spread over the north temperate zone, we can only explain their presence with us and not further east by something favourable either in our insular climate or in the limited competition due to our comparative poverty in species.

About half of the peculiar forms are found in the extreme west or north of Britain or in Ireland, where peculiar insular conditions are at a maximum; and the influence of these conditions is further shown by the number of species of West or South European plants which occur in the same districts.

We may here notice the interesting fact that Ireland possesses no less than twenty species or sub-species of flowering plants not found in Britain, and some of these _may_ be altogether peculiar. As a whole they show the effect of the pre-eminently mild and insular climate of Ireland in extending the range of some south European species. The following list of these plants, for which I am indebted to Mr. A. G. More, with a few remarks on their distribution, will be found interesting:--

LIST OF IRISH FLOWERING PLANTS WHICH ARE NOT FOUND IN BRITAIN.

1. _Polygala vulgaris_ (_var._ grandiflora). Sligo.

2. _Campanula rotundifolia_ (_var._ speciosa). W. Ireland.

3. _Arenaria ciliata._ W. Ireland (also Auvergne, Pyrenees, Crete).

4. _Saxifraga umbrosa._ W. Ireland (also Pyrenees, N. Spain, Portugal).

5. ,, _geum._ S. W. Ireland (also Pyrenees).

6. ,, _hirsuta._ S. W. Ireland (also Pyrenees).

7. _Inula salicina._ W. Ireland (Scandinavia, Middle and South Europe).

8. _Erica mediterranea._ W. Ireland (W. France, Spain, Portugal).

9. ,, _mackaiana_ (_tetralix_ sub.-sp.) W. Ireland (Spain).

10. _Arbutus unedo._ S. W. Ireland (W. of France, Spain, Portugal and
shores of Mediterranean).

11. _Dabeocia polifolia._ W. Ireland (W. of France, Spain and
Portugal).

{365} 12. _Pinguicula grandiflora._ S. W. Ireland (Spain, Pyrenees,
Alps of France and Switzerland).

13. _Neotinea intacta._ W. Ireland (S. France, Portugal, Spain, and
shores of Mediterranean).

14. _Spiranthes romanzoviana._ S. W. Ireland (North America).

15. _Sisyrinchium angustifolium._ W. Ireland (North America, Arctic and
Temp.).

16. _Potamogeton lonchites._ Ireland, Mr. Arthur Bennett informs me
that this is certainly not British or European, but may possibly be
identical with _P. fluitans_ _var._ _Americanus_ of the U. States.

17. _Potamogeton kirkii_ (_natans_ sub.-sp.). W. Ireland. (Arctic
Europe?)

18. _Eriocaulon septangulare._ W. Ireland, Skye, Hebrides (North
America).

19. _Carex buxbaumii._ N. E. Ireland, on an island in Lough Neagh
(Arctic and Alpine Europe, North America).

20. _Deyeuxia neglecta_ (_var._ _Hookeri_). On the shores and islands
of Lough Neagh. (And in Germany, Arctic Europe, and North America.)

We find here nine south-west European species which probably had a wider range in mild preglacial times, and have been preserved in the south and west of Ireland owing to its milder climate. It must be remembered that during the height of the glacial epoch Ireland was continental, so that these plants may have followed the retreating ice to their present stations and survived the subsequent depression. This seems more probable than that so many species should have reached Ireland for the first time during the last union with the continent subsequent to the glacial epoch. The Arctic, Alpine, and American plants may all be examples of species which once had a wider range, and which, owing to the more favourable conditions, have continued to exist in Ireland while becoming extinct in the adjacent parts of Britain and Western Europe.

As contrasted with the extreme scarcity of peculiar species among the flowering plants, it is the more interesting and unexpected to find a considerable number of peculiar mosses and Hepaticae, some of which present us with phenomena of distribution of a very remarkable character. For the following lists and the information as to the distribution of the genera and species I am indebted to Mr. William Mitten, one of the first authorities on these beautiful little plants. That of the mosses has been corrected for this edition by Dr. R. Braithwaite, and several species of hepaticae have been added by Mr. Mitten. {366}

LIST OF THE SPECIES OF MOSSES AND HEPATICAE WHICH ARE PECULIAR TO THE BRITISH ISLES (OR NOT FOUND IN EUROPE).

(_Those belonging to non-European genera in Italics._)

MOSSES.

1. Systegium Mittenii South England.
2. Campylopus Shawii North Britain.
3. ,, setifolius Ireland, Wales, and Hebrides.
4. Seligeria calcicola South England.
5. Pottia viridifolia South England.
6. Leptodontium recurvifolium Ireland and Scotland.
7. Tortula Hybernica Ireland.
8. _Streptopogon gemmascens_ Sussex.
9. Bryum barbatum Scotland.
10. _Bartramidula Wilsoni_ Ireland, Wales, and Scotland.
11. _Daltonia splachnoides_ Ireland, Antilles, and Mexico.
12. _Hookeria laetevirens_ Ireland, Cornwall, and Madeira.
13. Hypnum micans Ireland.
14. Myurium Hebridarium Hebrides and Atlantic Islands.
15. Hedwigia ciliata _var._ striata Wales and Scotland.

HEPATICAE.

1. Frullania germana Ireland.
2. ,, Hutchinsiae Ireland, Scotland, Wales, Devon,
Tropical regions.
3. Lejeunia flava Ireland, Atlantic Islands, S. America,
Africa, &c.
4. ,, microscopica Ireland, Wales, Cumberland, Madeira.
5. ,, Holtii Ireland (Killarney).
6. ,, diversiloba Ireland (Killarney), Mexico?
7. ,, patens Ireland.
8. Radula tenax Ireland.
9. ,, Holtii Ireland.
10. ,, voluta Ireland, Wales, Cumberland, Mexico?
11. ,, Carringtonii Ireland.
12. Lepidozia Pearsoni Wales.
13. Adilocolia decipiens Ireland, Wales, Africa, and S. America.
14. Cephalozia aeraria Wales.
15. Lophocolia spicata Ireland, Cornwall, Anglesea.
16. Martinellia nimbosa Ireland (Brandon Mountain).
17. Plagiochila spinulosa Wales, Ireland, and Scotland, Atlantic
Islands.
18. ,, ambagiosa Ireland, India.
19. Jamesoniella Carringtonii Scotland.
20. Gymnocolea Nevicensis Scotland.
21. Jungermannia Doniana Scotland.
22. Cesia crenulata Ireland, Wales.
23. Chasmatocolea cuneifolia Ireland.
24. Aerobolbus Wilsoni Ireland, S. America, New Zealand.
25. Petalophyllum Ralfsii Ireland, Cornwall, Devon.

{367}

Many of the above are minute or obscure plants, and are closely allied to other European species with which they may have been confounded. We cannot therefore lay any stress on these individually as being absent from the continent of Europe so much of which is imperfectly explored, though it is probable that several of them are really confined to Britain. But there are a few--indicated by italics--which are in a very different category; for they belong to genera which are altogether unknown in any other part of Europe, and their nearest allies are to be found in the tropics or in the southern hemisphere. The four non-European genera of mosses to which we refer all have their maximum of development in the Andes, while the three non-European Hepaticae appear to have their maximum in the temperate regions of the southern hemisphere. Mr. Mitten has kindly furnished me with the following particulars of the distribution of these genera:--

BARTRAMIDULA. Asia, Africa, S. America and Australia, but not Europe or
N. America.

STREPTOPOGON is a comparatively small genus, with seven species in the
Andes, one in the Himalayas, and three in the south temperate zone,
besides our English species.

DALTONIA is a large genus of inconspicuous mosses, having seventeen
species in the Andes, two in Brazil, two in Mexico, one in the
Galapagos, six in India and Ceylon, five in Java, two in Africa, and
three in the Antarctic Islands, and one in Ireland.

HOOKERIA (restricting that term to the species referable to
Cyclodictyon) is still a large genus of handsome and remarkable mosses,
having twenty-six species in the Andes, eleven in Brazil, eight in the
Antilles, one in Mexico, two in the Pacific Islands, one in New
Zealand, one in Java, one in India, and five in Africa--besides our
British species, which is found also in Madeira and the Azores but in
no part of Europe proper.

These last two are very remarkable cases of distribution, since Mr. Mitten assures me that the plants are so markedly different from all other mosses that they would scarcely be overlooked in Europe.

The distribution of the non-European genera of Hepaticae is as follows:--

CHASMATOCOLIA. South America and Ireland.

ACROBOLBUS. A small genus found only in New Zealand and the adjacent
islands, besides Ireland.

{368} PETALOPHYLLUM. A small genus confined to Australia and New
Zealand in the southern hemisphere, Algeria, and Ireland in the
northern. We have also one of the Hepaticae--_Mastigophora
Woodsii_--found in Ireland and the Himalayas, but unknown in any part
of continental Europe. The genus is most developed in New Zealand.

These are certainly very interesting facts, but they are by no means so exceptional in this group of plants as to throw any doubt upon their accuracy. The Atlantic islands present very similar phenomena in the _Rhamphidium purpuratum_, whose nearest allies are in the West Indies and South America; and in three species of Sciaromium, whose only allies are in New Zealand, Tasmania, and the Andes of Bogota. An analogous and equally curious fact is the occurrence in the Drontheim mountains in Central Norway, of a little group of four or five peculiar species of mosses of the genus Mnium, which are found nowhere else; although the genus extends over Europe, India, and the southern hemisphere, but always represented by a very few wide-ranging species except in this one mountain group![85]

Such facts show us the wonderful delicacy of the balance of conditions which determine the existence of particular species in any locality. The spores of mosses and Hepaticae are so minute that they must be continually carried through the air to great distances, and we can hardly doubt that, so far as its powers of diffusion are concerned, any species which fruits freely might soon spread itself over the whole world. That they do not do so must depend on peculiarities of habit and constitution, which fit the different species for restricted stations and special climatic conditions; and according as the adaptation is more general, or the degree of specialisation extreme, species will have wide or restricted ranges. Although their fossil remains have been rarely detected, we can hardly doubt that mosses have as high an antiquity as ferns or Lycopods; and coupling this antiquity with their great powers of dispersal we may understand how many of the genera have come to occupy a number of detached areas scattered over the whole earth, but {369} always such as afford the peculiar conditions of climate and soil best suited to them. The repeated changes of temperature and other climatic conditions, which, as we have seen, occurred through all the later geological epochs, combined with those slower changes caused by geographical mutations, must have greatly affected the distribution of such ubiquitous yet delicately organised plants as mosses. Throughout countless ages they must have been in a constant state of comparatively rapid migration, driven to and fro by every physical and organic change, often subject to modification of structure or habit, but always seizing upon every available spot in which they could even temporarily maintain themselves.[86]

Here then we have a group in which there is no question of the means of dispersal; and where the difficulties that present themselves are not how the species reached the remote localities in which they are now found, but rather why they have not established themselves in {370} many other stations which, so far as we can judge, seem equally suitable to them. Yet it is a curious fact, that the phenomena of distribution actually presented by this group do not essentially differ from those presented by the higher flowering plants which have apparently far less diffusive power, as we shall find when we come to treat of the floras of oceanic islands; and we believe that the explanation of this is, that the life of _species_, and especially of _genera_, is often so prolonged as to extend over whole cycles of such terrestrial mutations as we have just referred to; and that thus the majority of plants are afforded means of dispersal which are usually sufficient to carry them into all suitable localities on the globe. Hence it follows that their actual existence in such localities depends mainly upon vigour of constitution and adaptation to conditions just as it does in the case of the lower and more rapidly diffused groups, and only partially on superior facilities for diffusion. This important principle will be used further on to afford a solution of some of the most difficult problems in the distribution of plant life.[87]

_Concluding Remarks on the Peculiarities of the British Fauna and Flora._--The facts, now I believe for the first time brought together, respecting the peculiarities of the British fauna and flora, are sufficient to show that there is considerable scope for the study of geographical distribution even in so apparently unpromising a field as one of the most recent of continental islands. Looking at the general bearing of these facts, they prove, that the idea so generally entertained as to the biological identity of the British Isles with the adjacent continent is not altogether correct. Among birds we have undoubted peculiarities in at least three instances; peculiar fishes are much more numerous, and in this case the fact that the Irish species {371} are almost all different from the British, and those of the Orkneys distinct from those of Scotland, renders it almost certain that the great majority of the fifteen peculiar British fishes are really peculiar and will never be found on the European Continent. The mosses and Hepaticae also have been sufficiently collected in Europe to render it pretty certain that the more remarkable of the peculiar British forms are not found there; why therefore, it may be well asked, should there not be a proportionate number of peculiar British insects? It is true that numerous species have been first discovered in Britain, and, subsequently, on the continent; but we have many species which have been known for twenty, thirty, or forty years, some of which are not rare with us, and yet have never been found on the continent. We have also the curious fact of our outlying islands, such as the Shetland Isles, the Isle of Man, and the little Lundy Island, possessing each some peculiar forms which, _certainly_, do not exist on our principal island which has been so very thoroughly worked. Analogy, therefore, would lead us to conclude that many other species or varieties would exist on our islands and not on the continent; and when we find that a very large number (150) in three orders only, are so recorded, we may I think be sure that some considerable portion of these (though how many we cannot say) are really endemic British species.

The general laws of distribution also lead us to expect such phenomena. Very rare and very local species are such as are becoming extinct; and it is among insects, which are so excessively varied and abundant, which present so many isolated forms, and which, even on continents, afford numerous examples of very rare species confined to restricted areas, that we should have the best chance of meeting with every degree of rarity down to the point of almost complete extinction. But we know that in all parts of the world islands are the refuge of species or groups which have become extinct elsewhere; and it is therefore in the highest degree probable that some species which have ceased to exist on the continent should be preserved in some part or other of our islands, especially {372} as these present favourable climatic conditions such as do not exist elsewhere.

There is therefore a considerable amount of harmony in the various facts adduced in this chapter, as well as a complete accordance with what the laws of distribution in islands would lead us to expect. In proportion to the species of birds and fresh-water fishes, the number of insect-forms is enormously great, so that the numerous species or varieties here recorded as not yet known on the continent are not to be wondered at; while it would, I think, be almost an anomaly if, with peculiar birds and fishes there were _not_ a fair proportion of peculiar insects. Our entomologists should, therefore, give up the assumption, that all our insects do exist on the continent, and will some time or other be found there, as not in accordance either with the evidence or the probabilities of the case; and when this is done, and the interesting peculiarities of some of our smaller islands are remembered, the study of our native animals and plants, in relation to those of other countries, will acquire a new interest. The British Isles are said to consist of more than a thousand islands and islets. How many of these have ever been searched for insects? With the case of Lundy Island before us, who shall say that there is not yet scope for extensive and interesting investigations into the British fauna and flora?

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