tested, and in three cases very successfully. The seeds of Potamogeton,
Sparganium, and of the Cyperaceæ germinated readily in water, but few of
them failing, the process beginning in a few days or a few weeks. At
that time I was conducting an extended series of observations on the
postponement of germination of the seeds of aquatic plants, the results
of which were published in the _Proceedings of the Royal Physical
Society of Edinburgh_ for 1897. It was there shown that the seeds of
these plants often postpone their germination to the second and even to
the third spring. It thus happened that, whilst seeds obtained from the
stomach and intestines of the wild duck germinated in a few days or
weeks, I had to wait often a year and more for such a result with seeds
in their ordinary condition. This was well brought out in another
experiment made on a domestic duck, which I have described on page 369.
That wild ducks are to be regarded in the light of “flying germinators”
is thus very evident.
_Summary._
(1) In explanation of the shifting of the source of the Polynesian
plants from the New to the Old World, it is suggested that during the
glaciation of the northern hemisphere the Indo-Malayan plants entering
this region were “cornered” in the tropical Western Pacific, and were
only set free after the cold period had passed away, when they overran
Polynesia.
(2) Whilst the age of the Conifers is placed in the Mesozoic period,
that of the Compositæ is accredited to the Tertiary period, and the era
of Malayan immigration followed the glacial epoch.
(3) The suspension to a great extent of the agencies of plant dispersal
in the Pacific in later times is connected with a general principle
affecting the whole plant-world. With the secular drying up of the globe
the differentiation of climate, bird, and plant have gone on together,
the range of the bird being mainly controlled by the climate and the
range of the plant being largely dependent on the bird.
(4) Accepting Hawaii as entirely insular in its history, it is pointed
out that the principles deducible from the study of its flora can be
applied to the forest-flora of New Zealand, with the exception of the
Conifers and some genera that are ancient denizens of Antarctic
latitudes, and indicate a remote continental age dating back to the
Mesozoic period. It is suggested that the Indo-Malayan element in its
flora arrived there during the glaciation of the northern hemisphere.
(5) Insects and bats have probably been effective agents in
seed-dispersal in the Pacific, and it is shown that sea-birds carry
seeds in their stomach and intestines as well as in their feathers.
(6) It is shown that birds of the grouse family, gulls, and geese are
active seed-dispersers in cold northern latitudes, and that the
discussion of their influence in stocking Spitzbergen with its plants
reproduces many of the points of the controversy concerning the floras
of the continental islands of the South Pacific.
(7) The results of experiments and observations are cited to establish
the efficacy of ducks in distributing the seeds of aquatic plants, the
seeds ejected in their droppings germinating in a few days or weeks,
whilst those remaining in the pond or river often do not germinate for a
year or more.
CHAPTER XXXIV
GENERAL ARGUMENT AND CONCLUSION
THE problems concerned in the study of the floras of the Pacific islands
from the standpoint of dispersal are here approached through the buoyant
quality of the seed and fruit; and it is shown when dividing the plants
into two groups, those with buoyant and those with non-buoyant seeds or
fruits, that there has been at work through the ages a great sorting
process, by which the plants belonging to the group first named have
been mostly gathered at the coast. Its operation may be also observed
within the limits of a genus, where the species possessing seeds or
fruits that float is stationed at the coast, whilst the species with
seeds or fruits that sink makes its home inland.
When the principle here involved is applied to the British flora, it
presents itself as part of a much wider principle, by which plants
endowed with buoyant seeds and fruits have been stationed at the
water-side, whether on a river-bank, or beside a lake or pond, or on a
sea-beach. The broader principle proves in its turn to belong to a far
larger scheme, in which the fitness or unfitness of a plant to live in a
physiologically dry station appears as the primary determining quality,
the xerophyte (the plant of the dry station), provided with buoyant seed
or fruit, finding its way to the coast, and the hygrophyte (the plant
growing under more moist conditions), that is similarly endowed,
establishing itself by the side of the river, or the lake, or the pond.
When dealing with the general character and composition of the
strand-plants of the tropical Pacific, it is shown that in Fiji the
beach-plants often assert their primary xerophilous habit or fitness for
occupying any dry station by extending into the inland plains on the dry
sides of the islands. The Fijian shore-plants are divided into three
formations, those of the beach, those of the mangrove-swamp, and those
of intermediate stations on the borders of the swamps. The great
majority of the Fijian shore-plants are dispersed by the currents. The
Tahitian Islands, which are representative of Eastern Polynesia, lack
the mangroves and most of the plants that grow at the margin of a
mangrove-swamp; and their strand-flora is mainly composed of plants of
the beach, such as are dispersed by the currents far and wide in
tropical regions. The Hawaiian strand-flora is very meagre in its
character, lacking not only the plants of the mangrove and intermediate
formations, but almost all the large-fruited beach-trees of the South
Pacific. Since Hawaii possesses but few current-dispersed shore-plants
that are not found in the New World, reasons are given for the inference
that such shore-plants were originally brought by the currents from
America, and not from the South Pacific.
We are led on various grounds to the conclusion that tropical
shore-plants distributed by currents belong to two great regions, the
American including the west coast of Africa, and the Asiatic, or Old
World Region, which includes the African east coast. It is held that
America is so placed with regard to the currents, that it is a
distributor, and not a recipient of tropical shore-plants dispersed by
that agency. From this it follows that all cosmopolitan tropical
beach-plants that are dispersed by the currents have their homes in
America.
The results of observation and experiment are given to show that there
is no direct relation between the specific weight of seeds and fruits
and the density of sea-water. Yet, although the floating or sinking of a
seed or fruit is but an accidental attribute, it has had indirectly a
far-reaching influence not only on plant-distribution, but on
plant-development. In accordance with this want of relation between the
specific weight of seeds and fruits and the density of sea-water, the
great variety of structures concerned with buoyancy are regarded in the
main, after a detailed examination of their character, as not arising
from adaptation. Rather, it is urged, is buoyancy connected with
structures that now serve a purpose for which they were not originally
developed. Nature, it is held, has never concerned herself directly with
providing means of dispersal of any sort.
In the discussion of the relation between the littoral and inland
Pacific floras, it is shown, as a result of the examination of those
genera possessing both shore and inland species, that they have been on
the whole developed on independent lines. Two special difficulties in
explaining the modes of dispersal of plants of the Pacific islands here
come into prominence. There is the Hawaiian difficulty, where with
genera containing both shore and inland species only the last are found
in Hawaii; and although the shore-plants are known to be dispersed by
the current, the inland plants display little or no capacity for this or
any other mode of dispersal. Here belong the Leguminous genera
Canavalia, Erythrina, Mezoneuron, and Sophora, and the Apocynaceous
genus Ochrosia; and it is assumed that the inland Hawaiian species are
derived from a current-dispersed shore-plant that has since disappeared
from the group. The Fijian difficulty is displayed in those genera where
both coast and inland species occur in the islands, but no known
existing means of dispersal across an ocean can be postulated for the
inland plants, though the shore species are distributed by the currents.
Of such genera Pandanus is the best example, and it is pointed out that
this genus presents the same difficulty in the Mascarene Islands, in
which case the agency of the extinct Columbæ is invoked.
As illustrating the methods of observation and experiment employed by
the author, the Leguminous shore-plants Afzelia bijuga, Cæsalpinia
bonducella, and Entada scandens are discussed at length; and in the
chapters on the enigmas of the Leguminosæ in the Pacific it is pointed
out that the behaviour of the plants of this order is a source of much
perplexity, and that they conform to no single rule of dispersal.
Coming to the inland plants of this region, the Fijian, Tahitian, and
Hawaiian groups are taken as the chief centres of distribution in the
Pacific. After discussing the relative sizes, the altitudes, and the
climates of these three archipelagoes, it is shown that Hawaii, on
account of the far greater altitude of the islands, is characterised by
a special mountain flora, and that it is comparable with Fiji, and to a
great extent also with Tahiti, only as regarding the plants of the
levels below 4,000 or 5,000 feet.
The first era of the plant-stocking is designated the Age of Ferns, and
it is observed that, whilst in Hawaii nearly half of the ferns and
lycopods are peculiar to that group, very few new species have been
developed in the Fijian and Tahitian regions.
The next era in the floral history of these islands is represented in
the first era of the flowering plants. This is indicated by the endemic
genera, which are particularly numerous in Hawaii, relatively scanty in
Fiji, and very few in Tahiti. On account of their preponderance, the era
is designated the Age of Compositæ and Lobeliaceæ. The genera of these
two orders, though mainly characteristic of Hawaii, are also to be found
in the Tahitian region, but they are absent from the Fijian area.
Chiefly American in their affinities, their dispersion over the Pacific
took place during the Tertiary submergence of the archipelagoes of the
Western Pacific, in which are included the groups of the Fijian area
(Fiji, Samoa, Tonga). These early forms of Compositæ and Lobeliaceæ are
often arborescent in habit; and it is observed that Tree-Lobelias also
occur high up the slopes of lofty mountains in tropical regions, as in
Equatorial Africa, under conditions similar to those prevailing on the
slopes of the Hawaiian mountains, where the Tree-Lobelias, termed by Dr.
Hillebrand “the pride of our flora,” abound.
The other Hawaiian endemic genera, marking the first chapter in the
history of the flowering plants, arrange themselves in two groups, one
chiefly American in general affinities, and containing highly
differentiated Caryophyllaceæ, Labiatæ, &c.; the other largely Malayan,
and indicating the close of the first era of the flowering plants, when
the main source of the plants was shifted from America to the Old World.
The Fijian endemic genera, which are few in number, miscellaneous in
appearance, and disconnected in character, are regarded as having
probably acquired their endemic reputation through their failure at
their sources in the regions to the west.
The second era of the flowering plants is indicated by the non-endemic
genera. Here we are concerned on the one hand with a mountainous flora
mainly Hawaiian, in which genera from the New Zealand and Antarctic
floras take a conspicuous part, and on the other with a low-level flora
chiefly derived from Indo-Malaya, and including the plants of the lower
slopes of Hawaii below 4,000 and 5,000 feet, and the floras in mass of
Fiji and Tahiti.
On account of their lower altitude, the extensive mountain flora of
Hawaii is but scantily developed in Tahiti, and is represented by a mere
remnant in Fiji and Samoa. Two-thirds of the Hawaiian non-endemic
mountain genera contain only species restricted to the group, and,
although amongst these disconnected genera, Acæna, Gunnera, Coprosma,
Lagenophora, &c., of the New Zealand and Antarctic floras take a
prominent part, a large proportion of the genera like Ranunculus, Rubus,
Artemisia, Vaccinium, and Plantago represent generally the flora of the
north temperate zone on the summits of tropical mountains. The Tahitian
mountain flora, scanty as it is when judged by the non-endemic genera,
displays much kinship with the Hawaiian mountain flora; but this kinship
is mainly confined to genera from high southern latitudes, such as
Coprosma, Cyathodes, Astelia, &c. In the possession on its mountain
slopes of the three genera of the Coniferæ, Dammara, Podocarpus, and
Dacrydium, the Fijian region is distinguished from that of Tahiti and
Hawaii; and it is assumed that they mark the site of a continental area
in the Mesozoic period, when the Tahitian and Hawaiian groups did not
exist.
The era of the non-endemic genera, in so far as it is concerned with the
low-level flora of Hawaii and the floras in mass of the areas of Fiji,
Samoa and East Polynesia, is termed Malayan, because many of the genera
are thence derived. Here we are dealing with all the oceanic groups of
the tropical Pacific, and not with a portion of them, as in the case of
the Age of Coniferæ, in the Secondary period, that was limited to the
Western Pacific, or in the case of the Age of Compositæ and Lobeliaceæ
that was restricted during the Tertiary epoch to the Hawaiian and
Tahitian regions. The first part of this era, as is indicated by the
endemic species, is an age of complete isolation in Hawaii, and of
partial isolation in the groups of the southern region. Amongst the
genera typical of this period are Pittosporum, Gardenia, Psychotria,
Cyrtandra, and Freycinetia. A later period in this era of the general
dispersal of Malayan plants over the Pacific is one where the extremely
variable or polymorphous species plays a conspicuous part, as
represented in such genera as Alphitonia, Dodonæa, Metrosideros,
Pisonia, and Wikstrœmia, the general principle being that each genus is
at first represented by a widely ranging very variable species, which
ultimately ceases to wander and settles down, and becomes the parent of
different sets of species in the several groups.
The facts of distribution in this age of general dispersion are just
such as we might look for in the case of a general dispersal over the
oceanic groups of the Pacific, with the altitudes of the islands playing
a determining part. But it should be remarked that the greater number of
the genera that have entered the Pacific from the Old World have not
advanced eastward of the Fijian region, half of the Fijian genera not
occurring in the Hawaiian and Tahitian regions. The explanation of this
is to be found, not in any lack of capacities for dispersal, but in a
want of opportunities. The story of plant-distribution in the Pacific is
bound up with the successive stages of decreasing activity in the
dispersing agencies. The area of active dispersion, as illustrated by
the non-endemic genera, at first comprised the whole of the tropical
Pacific. It was afterwards restricted to the South Pacific, and finally
to the Western Pacific only. The birds that carried seeds all over this
ocean became more and more restricted in their ranges, probably on
account of increasing diversity of climatic conditions. The plants of
necessity responded to the ever narrowing conditions of bird-life in
this ocean, and the differentiation of the plant and the bird have taken
place together.
During the stages of decreasing activity in the dispersing agencies, the
widely-ranging highly variable species continued to be an important
factor in the development of new species in the different groups. The
_rôle_ of the polymorphous species has always been a conspicuous one in
the Pacific.
Yet, as in the case of the Cyrtandras, it is shown that the display of
great formative power within a genus is not a peculiarity of an insular
flora; that the isolation of an oceanic archipelago does not exclusively
induce “endemism,” but only intensifies it; that the development of new
species may be nearly as active on a mountain in a continent as on an
island in mid-ocean; and that this is equally true of a land genus, like
Embelia, exposed to an infinite variety of conditions, and of an aquatic
genus, like Naias, where the conditions of existence are relatively
uniform all the world over.
In framing a scheme by which the eras of the floral history of the
Pacific are brought into correlation with those of geological time, the
age of the Coniferæ is placed in the Secondary period, that of the
Compositæ and Lobeliaceæ in the Tertiary period, whilst the era of
Malayan immigration is regarded as mainly post-glacial. The age of the
Coniferæ is concerned only with the Western Pacific, since the Hawaiian
and Tahitian islands had not then been formed. The age of the Compositæ
and Lobeliaceæ is concerned only with Hawaii and Tahiti, since the
islands of the Western Pacific were then more or less submerged. That of
the Malayan plants affects the whole Pacific as at present displayed to
us.
In the chapter on the viviparous mangroves of Fiji it is shown that both
the Asiatic and the American species of Rhizophora (R. mucronata and R.
mangle) exist in that group, and that there is in addition a seedless
form, the Selala, which, although intermediate in character between the
two other species, comes nearest to the Asiatic plant. Reasons are given
for the belief that the Selala is derived from the Asiatic species (R.
mucronata), not as the result of a cross but as connected with its
dimorphism; and in support of this it is pointed out that on the Ecuador
coast of South America, where only the American species exists, a
dimorphism is also displayed, one of the forms approaching in several of
its characters the Fijian Selala, though fruiting abundantly and bearing
the impress of a closer connection with the typical American species
than with the Asiatic plant. The view that Rhizophora mangle reached the
Western Pacific from America is rejected, and it is considered that this
species was originally as widely diffused in the Old World as in
America, and that it now survives only in a few places in the tropics of
the Old World. The results of detailed observations on the modes of
dispersal and on the germinating process both with Rhizophora and
Bruguiera are given; and the absence, as a general rule, of any period
of rest between the fecundation of the ovule and the germination of the
seed is established.
A special chapter is devoted to the significance of vivipary, and it is
considered that a record of the history of vivipary on the globe is
afforded in the scale of germinative capacity that begins with the
seedling hanging from a mangrove and ends with the seed that is detached
in an immature condition from an inland plant. It is suggested that with
the drying up of the planet in the course of ages the viviparous habit,
which was once nearly universal, has been for the most part lost except
in the mangrove swamp, which to some extent represents an age when the
earth was enveloped in cloud and mist and the atmosphere was saturated
with aqueous vapour. The lost habit is at times revived in the abnormal
vivipary of some inland plants, and traces of it are seen in the
abnormal structure of the seeds of some genera of the Myrtaceæ, like
Barringtonia, and in the seeds of genera of other orders. With the
desiccation of the planet and the emergence of the continents there has
been continual differentiation of climate resulting in seasonal
variation and in the development of the rest-period of the seed.
With the secular drying of the globe and the consequent differentiation
of climate is to be connected the suspension to a great extent of the
agency of birds as plant-dispersers in later ages, not only in the
Pacific Islands but over all the tropics. The changes of climate, bird,
and plant have gone on together, the range of the bird being controlled
by the climate, and the distribution of the plant being largely
dependent on the bird.
The history of climate, the history of the continents and of the oceans,
the history of life itself, but only in the sense below defined, all
belong to that of a desiccating world, or rather of a planet once
sunless and enveloped in mist and cloud, that through the ages has been
drying up. Life’s types were few and the sea prevailed, and one climate
reigned over the globe. With the diminution of the aqueous envelopes the
continents began to emerge, climates began to individualise, and
organisms commenced to differentiate, and thus the process has run on
through the past, ever from the general to the special both in the
organic and in the inorganic world.
The same story of a world drying up is told by the marine remains left
stranded far up some mountain slope, or by the bird akin to no other of
its kind that Time has stranded on some island in mid-Pacific. The bird
generalised in type that once ranged the globe is now represented over
its original range by a hundred different groups of descendants,
confined each to its own locality. Climate, once so uniform, now so
diversified, has by restricting the range of the bird favoured the
process of differentiation, and the plant dependent on the bird for its
distribution has in its turn responded to these changes.
The _rôle_ of the polymorphous species belongs alike to the plant and to
the bird. A species that covers the range of a genus varies at first in
every region and ultimately gives birth to new species in some parts of
its range. Then the wide-ranging species disappears and the original
area is divided up into a number of smaller areas each with its own
group of species. Each smaller area breaks up again, and forms, yet more
specialised, are produced; and thus the process of subdivision of range
and of differentiation of form goes along until each island in an
archipelago owns its bird and each hill and valley has its separate
plants. This is not the path that Evolution takes, since beyond lies
extinction whether of plant or of bird. Such is the upshot of the
process of differentiation exhibited in the development of species and
genera in the Pacific Islands, or, indeed, in any oceanic groups. It can
never do more than produce a Dodo or a Kiwi, or amongst the plants a
Tree-Lobelia.
Evolution here and elsewhere is a thing apart from species and genera,
which are but eddies on the surface of its stream. It is a scheme of
life introduced into a much conditioned world, and adaptation in endless
forms is the price it has had to pay. The whole story of life on this
earth is a story of a sacrifice, of an end to be won, but of a price to
be paid. Immortality is in the scheme, but death is the price of
adaptation. The same theme runs through our conceptions of the spiritual
life. There is the same duality, evolution adapting its scheme to the
exigencies of the physical world, the good principle ever in conflict
with the evil, and at times compelled to adapt itself to attain its
ends. There is the tale of adaptation in the one case and of sacrifice
in the other, and success is reached in both.
APPENDIX
LIST OF NOTES
Note 1. On the number of known species of Fijian flowering plants.
Note 2. The littoral plants of Fiji.
Note 3. Results of long flotation experiments on the seeds or
seedvessels of tropical littoral plants.
Note 4. Table illustrating the degree of buoyancy of the seeds and
fruits of inland Fijian plants.
Note 5. The inland Fijian plants possessing buoyant seeds or fruits.
Note 6. Table showing the degree of buoyancy of the seeds and fruits of
some inland Hawaiian plants.
Note 7. Some inland Hawaiian plants possessing buoyant seeds or fruits.
Note 8. The pyrenes of Morinda.
Note 9. The buoyancy of the fruits of Calophyllum.
Note 10. The buoyancy experiments on British plants.
Note 11. The effect of sea-water immersion on the germinating capacity
of seeds and seed-vessels.
Note 12. The buoyancy of the fruits of Galium aparine.
Note 13. The buoyancy of the seeds of Convolvulus sepium.
Note 14. Other long flotation experiments.
Note 15. The occurrence inland of Silene maritima.
Note 16. The buoyancy of the seeds or fruits of the British beach-plants
that also occur inland.
Note 17. The buoyancy of the seeds or fruits of the British littoral
plants that frequent salt-marshes and muddy shores.
Note 18. The buoyancy of the seeds or fruits of the British littoral
plants that are confined to the beach.
Note 19. On germination in sea-water.
Note 20. On the maximum heights reached by some shore plants in their
extension inland in Vanua Levu, Fiji.
Note 21. On the dwarfing of shore plants when extending inland in the
“talasinga” plains in Vanua Levu.
Note 22. The “talasinga” plains of Vanua Levu.
Note 23. Schimper’s grouping of the Indo-Malayan strand flora.
Note 24. Grouping of some of the characteristic plants of the strand
flora of Fiji.
Note 25. The strand flora of the Tahitian region.
Note 26. The Fijian shore plants not found in Tahiti.
Note 27. The intruders into the beach flora from the inland plants of
Tahiti.
Note 28. The littoral plants of the Hawaiian islands.
Note 29. Botanical notes on the coast plants of the Hawaiian islands.
Note 30. The beach drift of the Hawaiian islands.
Note 31. The inland extension of the shore plants of the Hawaiian
islands.
Note 32. The Fijian species of Premna.
Note 33. De Candolle’s list of plants dispersed exclusively by currents.
Note 34. The littoral plants of the eastern-most Polynesian islands.
Note 35. Distribution of the littoral plants with buoyant seeds or
fruits that occur in the Fijian, Tongan, Samoan, Tahitian, and
Hawaiian Groups.
Note 36. Hawaiian plants with buoyant seeds or fruits known to be
dispersed by the currents either exclusively or with the assistance of
frugivorous birds.
Note 37. On vivipary in the fruits of Barringtonia racemosa and Carapa
obovata.
Note 38. On the temperature and density of the surface water of the
estuaries of the Rewa River in Fiji and of the Guayaquil River in
Ecuador.
Note 39. On the Pacific species of Strongylodon.
Note 40. Precautions in testing seed-buoyancy.
Note 41. The buoyancy of the seeds of Convolvulus soldanella in
fresh-water and sea-water compared.
Note 42. On secular changes in sea-density.
Note 43. On the mucosity of small seeds and seed-like fruits when wet.
Note 44. Upon the effects of inland extension on the buoyancy of the
seeds or fruits of littoral plants.
Note 45. Tabulated results of the classification, according to
Schimper’s application of the Natural Selection Theory, of the buoyant
seeds and fruits of tropical littoral plants.
Note 46. On the modes of dispersal of the genus Brackenridgea.
Note 47. On the transport of gourds by currents.
Note 48. On the useless dispersal by currents of the fruits of the Oak
and of other species of Quercus, as well as of the Hazel (Corylus).
Note 49. On the distribution of Ipomœa pes capræ, Convolvulus
soldanella, and Convolvulus sepium.
Note 50. On the structure of the seeds and fruits of Barringtonia.
Note 51. On a common inland species of Scævola in Vanua Levu, Fiji.
Note 52. On the capacity for dispersal by currents of Colubrina
oppositifolia.
Note 53. On the genus Erythrina.
Note 54. On the genus Canavalia.
Note 55. The inland extension of Scævola kœnigii.
Note 56. On the capacity for dispersal by currents of Sophora tomentosa,
S. chrysophylla, and S. tetraptera.
Note 57. On the species of Ochrosia.
Note 58. On Pandanus.
Note 59. Seeds in petrels.
Note 60. Schimper on the halophilous character of littoral Leguminosæ
and of shore plants generally.
Note 61. Meteorological observations on the summit of Mauna Loa.
Note 62. On the relative proportion of vascular cryptogams in Fiji.
Note 63. On the table of vascular cryptogams of Tahiti, Hawaii, and
Fiji.
Note 64. On the distribution of the Tahitian ferns and lycopods.
Note 65. Distribution of some of the mountain ferns of Hawaii that are
not found either in Fiji or in Tahiti.
Note 66. Endemic genera of ferns in Hawaii.
Note 67. On the dispersal of Compositæ by birds.
Note 68. On some of the Hawaiian endemic genera excluding those of the
Compositæ and Lobeliaceæ.
Note 69. On the germination of Cuscuta.
Note 70. On beach-temperature.
Note 71. On the buoyancy of the seeds or seed-vessels of some Chilian
shore plants.
Note 72. On the southern limit of the mangrove formation in Ecuador.
Note 73. Additional note on the temperature of the dry coast of Ecuador,
between the island of Puna and the equator.
Note 74. Observations on the temperature of the Humboldt current from
Antofagasta northward between January and March, 1904.
Note 75. On the stranded massive corals of the genus Porites (?) found
on the coast of North Chile and Peru at Arica, Callao, and Ancon.
Note 76. Stranded pumice on English and Scandinavian beaches.
Note 77. On the mode of dispersal of Kleinhovia hospita.
Note 78. On the “Sea”, an unidentified wild fruit tree in Fiji.
Note 79. On willow-leaved river-side plants.
Note 80. Mr. Perkins on the Hawaiian Lobeliaceæ.
Note 81. On the vertical range of some of the most typical and most
conspicuous of the plants in the forests on the Hamakua slopes of
Mauna Kea, Hawaii.
Note 82. Aboriginal weeds.
Note 90. On the buoyancy of the seeds of Euphorbia amygdaloides and E.
segetalis.
Note 91. Mr. E. Kay Robinson on Aster tripolium.
NOTE 1 (page 13)
ON THE NUMBER OF KNOWN SPECIES OF FIJIAN FLOWERING PLANTS
Rather over 600 species of flowering plants are included in Seemann’s
_Flora Vitiensis_, excluding the weeds and the plants introduced by man.
Horne’s collections would probably add another 300 species; and many
more remain to be discovered.
NOTE 2 (page 13)
THE LITTORAL PLANTS OF FIJI
In the following table are incorporated the results of an extensive
series of observations and experiments on the buoyancy of the seeds and
fruits of the shore plants made by the author during his sojourn of two
years in Fiji, and based not only on prolonged buoyancy-tests, but also
on systematic examination of the stranded and floating seed-drift, both
of sea and river. The details would occupy many chapters: and it is only
possible here to give the bare results. Since Professor Schimper went
over much the same ground in the Malayan region, one enjoys in many
cases the great advantage of his authority; but a fair proportion of the
results are new; and, besides, there are a number of plants included,
the buoyancy of whose seeds or fruits has long been well established. In
all cases the seed or fruit is taken as it presents itself for dispersal
by the currents. Many of the plants are discussed with some detail in
various parts of this book, as indicated in the reference column of the
table.
Since the Gramineæ and the Cyperaceæ contain very few species suited for
direct transport by the currents over wide areas of sea, this list may
be regarded as containing nearly all the littoral flowering plants
possessing seeds or seed-vessels with any buoyancy of importance.
Nearly all the Tahitian strictly littoral plants are represented in
Fiji, and the few that have not been found there yet, such as Sesbania
grandiflora, Heliotropium anomalum, &c., may exist, as in the
first-named species, in the neighbouring Tongan group, and may probably
even exist in Fiji. Two other Tahitian littoral plants, that are widely
spread in the Pacific, namely, Suriana maritima and Sesuvium
Portulacastrum, are found in Tonga, and are included in my list of
Fijian shore plants, though not yet recorded from that group, where,
however, they will, without a doubt, be found by some future observer.
TABLE SHOWING THE BUOYANCY OF THE SEEDS OR FRUITS OF THE LITTORAL PLANTS
OF FIJI, EXCLUDING THE GRASSES AND, WITH ONE EXCEPTION, THE SEDGES
The letters placed before the plant name indicate that the species is
also found in Hawaii (H), in Tahiti (T), and in the Marquesas (M). The
Marquesan locality is only given where the plant is not in Tahiti.
The abbreviations in the reference column are as follows:
S=Schimper; G=Guppy; P=Earlier authorities and particularly the list
given by Hemsley in the Introduction to the _Botany of the Challenger
Expedition_.
Column headings:
A. Buoyancy of seeds or fruits.
B. Float for months.
C. Sink at once or in a week or two.
D. Authorities.
E. Pages of further reference. See also Index.
+--------------------------------------+--------------+-------+-------+--------+
| | | A | | |
| Species. | Family. +---+---+ D | E |
| | | B | C | | |
+--------------------------------------+--------------+---+---+-------+--------+
|HT Calophyllum inophyllum |Guttiferæ. | + |...|S.G.P. | 18 |
| | | | | | |
|HT Hibiscus tiliaceus |Malvaceæ. | + |...|S.G.P. | 21 |
| | | | | | |
| Hibiscus diversifolius (Jacq.) |Malvaceæ. | + |...|G. | 21 |
| | | | | | |
|HT Thespesia populnea |Malvaceæ. | + |...|S.G.P. | Note 3 |
| | | | | | |
| H Gossypium tomentosum (Nutt.) |Malvaceæ. |...| + |G. | |
| | | | | | |
| Heritiera littoralis |Sterculiaceæ. | + |...|S.G.P. | 45, 48 |
| | | | | | |
| T Kleinhovia hospita |Sterculiaceæ. | + |...|G. | 21 |
| | | | | | |
| T Triumfetta rhomboidea |Tiliaceæ. |...| +?| | |
| | | | | | |
| T Triumfetta procumbens |Tiliaceæ. |...| + |G. | 45 |
| | | | | | |
| T Suriana maritima |Simarubeæ. | + |...|S.G. | |
| | | | | | |
| Carapa moluccensis |Meliaceæ. | + |...|S.G.P. | 45 |
| | | | | | |
| Carapa obovata |Meliaceæ. | + |...|S.G.P. | 45 |
| | | | | | |
| T Ximenia americana |Olacineæ. | + |...|S.G. | 113 |
| | | | | | |
| Smythea pacifica (Seem.) |Rhamneæ. | + |...|G.P. | 106 |
| | | | | | |
|HT Colubrina asiatica |Rhamneæ. | + |...|G. | 137 |
| | | | | | |
|HT Dodonæa viscosa |Sapindaceæ. | + |...|S.G. | |
| | | | | | |
|HT Tephrosia piscatoria |Papilionaceæ. |...| + |G. | 45 |
| | | | | | |
| M Desmodium umbellatum |Papilionaceæ. |...| + |G. | |
| | | | | | |
|HT Dioclea violacea |Papilionaceæ. | + |...|G.P. | 82 |
| | | | | | |
| T Canavalia obtusifolia |Papilionaceæ. | + |...|S.G.P. |Note 54 |
| | | | | | |
| T Canavalia sericea |Papilionaceæ. | + |...|G. |Note 54 |
| | | | | | |
| T Canavalia ensiformis, var. turgida.|Papilionaceæ. | + |...|S.G.P.?|Note 54 |
| | | | | | |
|HT Mucuna gigantea |Papilionaceæ. | + |...|S.G.P. | 81 |
| | | | | | |
| T Erythrina indica |Papilionaceæ. | + |...|S.G.P. | |
| | | | | | |
|HT Strongylodon lucidum |Papilionaceæ. | + |...|G. | 82 |
| | | | | | |
|HT Vigna lutea |Papilionaceæ. | + |...|S.G. | 139 |
| | | | | | |
| Dalbergia monosperma |Papilionaceæ. | + |...|S.G. | 106 |
| | | | | | |
| Derris uliginosa |Papilionaceæ. | + |...|S.G.P. | 111 |
| | | | | | |
| Pongamia glabra |Papilionaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Sophora tomentosa |Papilionaceæ. | + |...|S.G. |Note 56 |
| | | | | | |
| T Inocarpus edulis |Papilionaceæ. | +?|...|G.P. | |
| | | | | | |
|HT Cæsalpinia Bonducella |Cæsalpinieæ. | + |...|S.G.P. | 193 |
| | | | | | |
| T Cæsalpinia Bonduc |Cæsalpinieæ. | + |...|G.P. | 193 |
| | | | | | |
| Afzelia bijuga |Cæsalpinieæ. | + |...|G. | 173 |
| | | | | | |
| Cynometra sp. |Cæsalpinieæ. | +?|...|S.G. | |
| | | | | | |
| Entada scandens |Mimoseæ. | + |...|G.P. | 181 |
| | | | | | |
| Acacia laurifolia |Mimoseæ. |...| + |G. | 164 |
| | | | | | |
| T Leucæna Forsteri |Mimoseæ. |...| + |G. | |
| | | | | | |
| T Serianthes myriadenia |Mimoseæ. |...| + |G. | 424 |
| | | | | | |
| Parinarium laurinum |Rosaceæ. | + |...|G.P. | |
| | | | | | |
| Eugenia Richii |Myrtaceæ. |...| + |G. | |
| | | | | | |
| T Barringtonia speciosa |Myrtaceæ. | + |...|S.G.P. | |
| | | | | | |
| Barringtonia racemosa |Myrtaceæ. | + |...|G. | |
| | | | | | |
| Rhizophora mucronata |Rhizophoreæ. | + |...|S.G.P. | |
| | | | | | |
| Rhizophora mangle |Rhizophoreæ. | + |...|S.G.P. | |
| | | | | | |
| Bruguiera Rheedii |Rhizophoreæ. | + |...|G.P. | |
| | | | | | |
|HT Terminalia Katappa |Combretaceæ. | + |...|S.G.P. | |
| | | | | | |
| M Terminalia littoralis |Combretaceæ. | + |...|S.G.P. | |
| | | | | | |
| Lumnitzera coccinea |Combretaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Gyrocarpus Jacquini |Combretaceæ. | + |...|G. | 423 |
| | | | | | |
| T Pemphis acidula |Lythraceæ. | + |...|S.G. | |
| | | | | | |
| T Luffa insularum (Gray) |Cucurbitaceæ. | + |...|G. | 426 |
| | | | | | |
|HT Sesuvium Portulacastrum |Ficoideæ. |...| + |G. | |
| | | | | | |
|HT Morinda citrifolia |Rubiaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Guettarda speciosa |Rubiaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Wedelia biflora |Compositæ. | + |...|G. | |
| | | | | | |
|HT Scævola Koenigii |Goodeniaceæ. | + |...|S.G.P. | |
+--------------------------------------+--------------+---+---+-------+--------+
TABLE SHOWING THE BUOYANCY OF THE SEEDS OR FRUITS OF THE
LITTORAL PLANTS OF FIJI, EXCLUDING THE GRASSES, AND WITH
ONE EXCEPTION, THE SEDGES (_continued_)
Column headings:
A. Buoyancy of seeds or fruits.
B. Float for months.
C. Sink at once or in a week or two.
D. Authorities.
E. Pages of further reference. See also Index.
+--------------------------------------+--------------+-------+-------+--------+
| | | A | | |
| Species. | Family +---+---+ D | E |
| | | B | C | | |
+--------------------------------------+--------------+---+---+-------+--------+
| T Cerbera Odollam |Apocynaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Ochrosia parviflora |Apocynaceæ. | + |...|G.P. | |
| | | | | | |
|HT Cordia subcordata |Boraginaceæ. | + |...|S.G.P. | |
| | | | | | |
| T Tournefortia argentea |Boraginaceæ. | + |...|S.G.P. | |
| | | | | | |
|HT Ipomœa pes capræ |Convolvulaceæ.| + |...|S.G.P. | |
| | | | | | |
| H Ipomœa glaberrima (Boj.) |Convolvulaceæ.| + |...|G. | |
| | | | | | |
| Aniseia uniflora |Convolvulaceæ.| + |...|G. | |
| | | | | | |
| T Premna tahitensis |Verbenaceæ. | + |...|G. |Note 32 |
| | | | | | |
| Clerodendron inerme |Verbenaceæ. | + |...|S.G. | |
| | | | | | |
|HM Vitex trifolia |Verbenaceæ. | + |...|G. | |
| | | | | | |
|HT Cassytha filiformis |Lauraceæ. | + |...|G. | |
| | | | | | |
| T Hernandia peltata |Lauraceæ. | + |...|S.G. | |
| | | | | | |
|HT Wikstrœmia fœtida |Thymelæaceæ. |...| + |G. | |
| | | | | | |
| Drymispermum Burnettianum |Thymelæaceæ. |...| + |G. | |
| | | | | | |
| T Euphorbia Atoto |Euphorbiaceæ. |...| + |S.P.G. | |
| | | | | | |
| Excæcaria Agallocha |Euphorbiaceæ. | + |...|S.G. | |
| | | | | | |
| T Casuarina equisetifolia |Casuarineæ. |...| + |G. | |
| | | | | | |
|HT Tacca pinnatifida |Taccaceæ. | + |...|G. | 19 |
| | | | | | |
|HT Cocos nucifera |Palmeæ. | + |...|P. | |
| | | | | | |
|HT Pandanus odoratissimus |Pandaneæ. | + |...|S.G.P. | |
| | | | | | |
| Crinum asiaticum |Amaryllideæ. |...| + |G.P. | |
| | | | | | |
| Scirpodendron costatum |Cyperaceæ. | + |...|G. | 407 |
| | | | | | |
| Cycas circinalis |Cycadeæ. | + |...|G.P. | |
+--------------------------------------+--------------+---+---+-------+--------+
NOTE 3 (page 13)
RESULTS OF LONG FLOTATION EXPERIMENTS ON THE SEEDS OR SEED-VESSELS OF
TROPICAL LITTORAL PLANTS
At various times during the past twenty years I have made lengthened
experiments in England on the buoyancy in sea-water of the seeds or
seed-vessels of beach plants collected by me in the Solomon Islands, the
Fijis, Hawaii, Keeling Atoll, &c. In all the species enumerated below,
the floating powers were retained after twelve months’ immersion, the
seed-contents being to all appearance unharmed. In six species I
succeeded in getting the seeds to germinate after the experiment; and
there can be no doubt that the number of successful results would have
been largely increased, if I had not been obliged to resort to very
primitive methods in conducting the experiments. Some of the results are
referred to in a note to my paper on the flora of Keeling Atoll, dated
about 1889; and if I remember aright, Mr. Hemsley mentioned those
relating to Thespesia populnea and Ipomœa grandiflora in the _Annals of
Botany_, not long after. The others have not been previously published.
In one instance (Cæsalpinia bonducella) the flotation experiment was
prolonged to two and a half years, the seeds floating buoyantly and
being apparently quite sound at the end of the experiment.
As demonstrating that tropical seeds can be transported unharmed by
currents through cold latitudes, it should be noted that all these
experiments were conducted in England. In the cases of the Keeling Atoll
seeds the experiment was carried on through a very severe winter, the
vessel of sea-water being exposed to a degree of cold that kept
fresh-water frozen for three weeks on the same table. This did not
prevent the subsequent germination of the seeds of Thespesia populnea
and Ipomœa grandiflora. The same thing was established in a more natural
way by Lindman, who planted seeds of Entada scandens and Mucuna urens,
that had been stranded on the Norwegian coast, and found that they
retained their germinating capacity (see Sernander, p. 7).
The following are the seeds or seed-vessels that remained afloat after a
year’s flotation in sea-water, those that subsequently germinated being
preceded by G. In the other cases the germinating capacity was not
tested; but they were always sound in appearance when cut across at the
close of the experiment.
G Thespesia populnea (Malvaceæ)
Dioclea (violacea?) (Papilionaceæ)
G Mucuna gigantea, D C (Papilionaceæ)
G Mucuna urens, D C (Papilionaceæ)
Mucuna, sp. (Papilionaceæ)
Mucuna, sp. (Papilionaceæ)
G Strongylodon lucidum, Seem. (Papilionaceæ)
Sophora tomentosa, (Papilionaceæ)
G Cæsalpinia bonducella (Cæsalpinieæ)
Entada scandens (Mimoseæ)
Morinda citrifolia (Rubiaceæ)
Scævola Koenigii (Goodeniaceæ)
Cordia subcordata (Boragineæ)
Tournefortia argentea (Boragineæ)
G Ipomœa grandiflora, Lam. (Convolvulaceæ)
Tacca pinnatifida (Taccaceæ)
NOTE 4 (page 13)
TABLE ILLUSTRATING THE DEGREE OF BUOYANCY OF THE SEEDS AND FRUITS OF
INLAND FIJIAN PLANTS
(Unless otherwise indicated, the seeds or fruits sink at once or in a
day or two)
Abrus precatorius.
Acacia Richii.
Ageratum conyzoides.
Alphitonia excelsa.
Alpinia sp.
Alyxia (scandens?).
Artocarpus incisa.
Artocarpus integrifolia.
Barringtonia edulis (1 month)
Barringtonia sp.
Bauhinia sp.
Bischoffia javanica.
Cæsalpinia sp.
Calophyllum spectabile (2-4 weeks).
Calophyllum Burmanni (4-10 days).
Cananga odorata.
Canarium sp.
Canarium sp.
Canna indica.
Citrus aurantium (3-4 weeks).
Citrus decumana (1 month).
Citrus limonum (5 weeks).
Citrus vulgaris, R. (6-7 weeks).
Coix lachryma (2-7 days).
Commersonia platyphylla.
Cordyline sepiaria.
Couthovia corynocarpa (a few days).
Cucumis acidus (a few days).
Cucurbita sp. (several months).
Cupania sp.
Dammara vitiensis (7-10 days).
Dioscorea sativa (a few days).
Dioscorea sp.
Dracontomelon sylvestre.
Dracontomelon sp.
Elæocarpus sp.
Elæocarpus sp. (a few days).
Eranthemum sp.
Eugenia malaccensis (2-4 weeks).
Eugenia effusa? (4-7 days).
Eugenia confertiflora? (10-12 days).
Eugenia rariflora (a few days).
Eugenia corynocarpa (a few days).
Eugenia rivularis (a week).
Fagræa Berteriana (a few days).
Ficus Harveyi (7-10 days).
Ficus scabra (7-10 days).
Ficus sp. (7-10 days).
Gardenia vitiensis (4-5 weeks).
Geissois ternata.
Geophila reniformis.
Gnetum gnemon.
Grewia sp.
Guettarda sp. (a few weeks).
Hibiscus Abelmoschus (months).
Hibiscus seculentus.
Hydrocotyle asiatica (months).
Ipomœa batatas.
Ipomœa insularis (_nil_ or months).
Ipomœa peltata (weeks or months).
Ipomœa turpethum (_nil_ or weeks or months).
Ipomœa sp. (7-10 days).
Lindenia vitiensis (weeks or months).
Maba sp. (7-10 days).
Macaranga sp. (1-2 weeks).
Melastoma denticulatum.
Micromelum minutum.
Momordica Charantia (a few days).
Morinda Forsteri.
Mussænda frondosa.
Myristica sp. (3-7 days)
Myristica sp. (3-7 days)
Myrmecodia sp.
Nelitris vitiensis (a few days).
Nephelium pinnatum (a few days).
Ophiorrhiza leptantha.
Phyllanthus sp.
Phyllanthus sp.
Piper Macgillivrayi.
Pittosporum sp.
Pleiosmilax vitiensis.
Portulaca (lutea?).
Portulaca quadrifida.
Premna serratifolia.
Pritchardia pacifica.
Psychotria sp.
Psychotria sp.
Psychotria sp.
Psychotria sp.
Psychotria sp.
Ptychosperma sp.
Rhaphidophora vitiensis.
Sapota sp. (a few days)
Sapota sp. (a few days)
Scævola floribunda.
Spondias dulcis (a month).
Sterculia sp. (seeds _nil_, fruits months).
Stylocoryne sambucina (2 or 3 days).
Tabernæmontana (orientalis?) (a few days).
Tacca maculata (_nil_ or a few days).
Trichospermum Richii (a few days).
Urena lobata.
Veitchia Joannis.
Veitchia sp.
NOTE 5 (page 14).
THE INLAND FIJIAN PLANTS POSSESSING BUOYANT SEEDS OR FRUITS
They come under the following heads:
(a) Plants of the stream-border or the pond-side or of the inland swamp,
_e.g._, Lindenia vitiensis and Hydrocotyle asiatica. The extension of
the principle by which plants with buoyant seeds or fruits are located,
not only at the sea-side but at the water-side generally, is here
involved, as explained in Chapter III.
(b) Plants following the rule deduced by Schimper for Terminalia, that
when a genus comprises several species possessing buoyant fruits, only
those having fruits with the greatest floating power are found at the
coast, the least buoyant plants occurring inland; examples, Calophyllum
and Guettarda.
(c) Plants that like Ipomœa behave irregularly in respect to
seed-buoyancy, a difference in behaviour often associated with varying
stations both at the coast and inland.
(d) Plants with dehiscent buoyant capsular fruits, like Sterculia, where
dehiscence takes place on the tree and the seeds have no buoyancy.
Although the unopened fruit may float a long time, it does not in that
condition come under the influence of the currents.
(e) Plants like Citrus Decumana, Gardenia, sp., &c., that, although
apparently exceptions to the principle, do not offer much opposition to
it, since the first is most at home at the river-side and the second
often displays a decided inclination for a station at the coast.
(f) Genuine exceptions to the principle, such as Hibiscus Abelmoschus
(see page 21).
NOTE 6 (page 15)
TABLE SHOWING THE DEGREE OF BUOYANCY OF THE SEEDS AND FRUITS OF SOME
INLAND HAWAIIAN PLANTS
(Unless otherwise stated, the seeds or fruits sink at once or in a day
or two)
Acacia Koa.
Aleurites moluccana (1-2 weeks).
Alyxia olivæformis.
Argemone mexicana.
Argyreia tiliæfolia (_nil_ or months).
Bidens pilosa.
Campylotheca sp.
Canavalia galeata.
Capparis sandwicensis.
Cassia Gaudichaudii.
Cassia occidentalis.
Cheirodendron Gaudichaudii.
Colubrina oppositifolia (weeks).
Commelina nudiflora.
Coprosma ernodeoides.
Coprosma sp.
Coprosma sp.
Cyathodes Tameiameiæ (a few days).
Cyrtandra sp. (a few days).
Cyrtandra sp. (a few days).
Cyrtandra sp. (a few days).
Dianella odorata (a few days).
Dracæna aurea.
Eclipta alba (months).
Erythrina monosperma.
Gossypium tomentosum (a week).
Gossypium barbadense (a few days).
Gossypium sp. cultiv. (a few days).
Hibiscus Youngianus (weeks).
Hydrocotyle verticillata (weeks).
Ipomœa bona nox (_nil_ or months).
Ipomœa insularis.
Ipomœa pentaphylla.
Ipomœa reptans.
Ipomœa tuberculata.
Jacquemontia sandwicensis.
Jussiæa villosa (a few days).
Lobeliaceæ (Clermontia).
Maba sandwicensis.
Metrosideros polymorpha.
Mezoneuron kauaiense (pod, a week).
Mucuna urens (months).
Myoporum sandwicense.
Olea sandwicensis, see page 364.
Phyllostegia grandiflora.
Phyllostegia mollis.
Plectronia odorata.
Pritchardia Gaudichaudii (5 or 6 weeks).
Ricinus communis (7-10 days).
Rubus Macraei.
Scævola Chamissoniana.
Scævola Gaudichaudii.
Sida fallax.
Sisyrinchium acre.
Solanum aculeatissimum.
Sophora chrysophylla (pod, 1-2 weeks).
Viola Chamissoniana.
Waltheria americana.
NOTE 7 (page 15)
SOME INLAND HAWAIIAN PLANTS POSSESSING BUOYANT SEEDS OR FRUITS
Three of these, Eclipta alba, Hibiscus Youngianus, and Hydrocotyle
verticillata, frequent wet places, and come under the principle that
water-side plants generally have buoyant seeds or fruits. The buoyancy
of the seeds of Argyreia tiliæfolia and of Ipomœa bona nox varies with
station and may be explained as under Ipomœa in Note 5. The floating
power of the fruits of Colubrina oppositifolia may be akin to that of
inland species of Terminalia as indicated in Note 5, since another
species of the genus C. asiatica, which is a coast plant, has very
buoyant seeds. Mucuna urens was no doubt originally, as it now is in
tropical America, a littoral plant. The buoyant fruits of Pritchardia
Gaudichaudii offer a genuine exception to the principle (see page 330).
NOTE 8 (pages 18, 112)
THE PYRENES OF MORINDA
The pyrenes of the two Malayan inland species of Morinda (M. umbellata
and M. longiflora) examined by Professor Schimper do not possess the
bladder-like cavity to which those of M. citrifolia owe their floating
power, and it is to be inferred from his remarks (p. 183) that they have
little or no buoyancy. The pyrenes of a Fijian inland species, near M.
Grayi, had no floating power as tested by me, and they lacked the
bladder-like cavity.
NOTE 9 (page 18)
THE BUOYANCY OF THE FRUITS OF CALOPHYLLUM
Professor Schimper found that whilst the fruits of Calophyllum
inophyllum, the shore tree, remained afloat after 126 days, those of C.
amœnum, an inland species, sank in from three to fourteen days, both
possessing similar buoyant structures, but to a less degree in the case
of the inland species. This genus presents a parallel case to Terminalia
referred to on page 17; but the general discussion of the subject will
be found in Chapter XIII. According to the above authority C. Calaba, a
West Indian coast tree, has buoyant fruits. The same is also true of the
fruits of a large inland tree in the Solomon Islands experimented on by
me (_Solomon Islands_, p. 305). It would thus appear that the fruits of
the genus are as a rule buoyant, and that, as in Terminalia, the least
buoyant fruits belong to the inland species. Professor Schimper also
shows (p. 182) that the diminished floating power of the fruits of the
inland species is associated with diminution in thickness of the buoyant
seed-shell which is most developed in the buoyant fruits of the strand
species.
NOTE 10 (page 24)
THE BUOYANCY EXPERIMENTS ON BRITISH PLANTS
The experiments in all cases were made to test the floating power of the
seed or fruit in the condition in which it is detached from the plant.
It usually makes very little difference whether sea-water or fresh water
is employed, since in my numerous experiments there were but few
exceptions to the general rule that seeds or seed-vessels that sink in
fresh water sink also in sea-water. This subject is discussed in Chapter
X. However, it may be here observed that the chief effect of the
increased density of sea-water is merely to increase the proportion of
buoyant seeds or fruits in any particular species.
It is necessary in such experiments to imitate Nature as much as
possible. The seed or fruit, as the case may be, must be experimented
upon in the condition in which it falls from the plant, or in the
condition in which it would be ultimately found in river and pond drift.
The seed or fruit should be thoroughly wetted, and air-bubbles removed.
Prolonged drying has but a slight effect on the great majority of seeds
and seed-vessels experimented on, and this is just as true of tropical
plants. Those that sink at once in the mature and fresh condition rarely
float more than a day or two even after drying for a year. The usual
effect is to increase the floating capacity of seeds and fruits already
buoyant, and not to develop the capacity.
The results given in the table refer only to sound seeds. In fresh-water
experiments, in nearly all cases, the seeds ultimately germinate in the
water, and this is the usual cause of the close of the experiment. In an
ordinary collection of floating seed drift from a pond or river,
germination will go on for years at each successive spring, the
postponement of germination being a very striking feature with a fair
proportion of seeds in river and pond-drift. This subject is dealt with
in detail in my paper published in the _Proceedings_ for 1897 of the
Royal Physical Society of Edinburgh.
THE TABLE OF RESULTS OF OBSERVATIONS AND EXPERIMENTS ON THE
BUOYANCY OF THE SEEDS OR SEED-VESSELS OF MORE THAN 300
BRITISH FLOWERING PLANTS
EXPLANATION OF TABLE.—The capacity of floating for months is thus
indicated, ++; of floating for 1 to 4 weeks, +; and where sinking occurs
at once or within a week there is no entry. When buoyancy continued in
my experiments after 6 and 12 months, it is indicated by Roman numerals
(VI and XII). A=an aquatic plant; M=a beach plant; R=a river-side or
pond-side plant; var.=variable in floating power.
+--------------------------------------+----+------+
|R Thalictrum flavum | | |
|A Ranunculus aquatilis | | |
|R Ranunculus hederaceus | | |
|R Ranunculus flammula | | |
| Ranunculus ficaria | | |
|R Ranunculus sceleratus VI | ++ | Var. |
| Ranunculus acris | | |
| Ranunculus repens XII | ++ | Var. |
|R Caltha palustris | + | |
| Berberis vulgaris | | |
|A Nymphæa alba | | |
|A Nuphar luteum | | |
| Papaver rhœas | | |
| Papaver dubium | | |
| Chelidonium majus | | |
| Rœmeria hybrida | | |
|M Glaucium luteum | | |
| Barbarea vulgaris | | |
|R Nasturtium officinale | | |
|R Nasturtium sylvestre | | |
|R Nasturtium amphibium | | |
| Arabis hirsuta | | |
| Arabis thaliana | | |
|R Cardamine pratensis | | |
| Cardamine hirsuta | | |
| Alliaria officinalis | | |
| Brassica campestris | | |
| Brassica alba | | |
|M Cochlearia officinalis | | |
|M Alyssum maritimum | | |
| Draba verna | | |
| Thlaspi arvense | | |
| Capsella bursa pastoris | | |
|M Cakile maritima | + | |
|M Crambe maritima | + | |
|M Raphanus maritimus | + | |
| Reseda luteola | | |
| Helianthemum vulgare | | |
|R Viola palustris | | |
| Viola canina | | |
| Viola tricolor | | |
| Polygala vulgaris | | |
| Silene cucubalus | | |
|M Silene maritima | | |
| Lychnis diurna | | |
| Sagina procumbens | | |
|M Arenaria peploides (Honckeneya) XII | ++ | |
| Mœnchia erecta | | |
| Cerastium vulgatum | | |
|R Stellaria aquatica | | |
| Stellaria media | | |
| Stellaria graminea | | |
| Stellaria holostea | | |
| Spergularia rubra | | |
|M Spergularia marina | | |
| Spergula arvensis | | |
|R Montia fontana | | |
|R Elatine hydropiper | | |
| Hypericum perforatum | | |
| Hypericum quadrangulum | | |
|R Hypericum elodes | | |
| Linum usitatissimum | | |
| Linum angustifolium | | |
| Malva rotundifolia | | |
| Malva sylvestris | | |
| Oxalis acetosella | | |
| Oxalis corniculata | | |
| Impatiens parviflora | | |
|R Impatiens fulva VI | ++ | |
| Acer campestre | | |
| Ilex aquifolium | | |
| Euonymus europæus | + | |
| Ulex europæus | | |
| Cytisus scoparius | | |
| Ononis arvensis | | |
| Medicago lupulina | | |
| Medicago denticulata | | |
| Trifolium incarnatum | | |
| Lotus corniculatus | | |
| Anthyllis vulneraria | | |
| Vicia sativa | | |
| Lathyrus pratensis | | |
|M Lathyrus maritimus | ++ | |
|R Spiræa ulmaria | + | |
| Fragaria vesca | | |
| Potentilla tormentilla | | |
| Potentilla sp. | | |
|R Potentilla comarum XII | ++ | |
| Alchemilla arvensis | | |
| Rosa arvensis | | |
| Cratægus oxyacantha | + | |
|R Epilobium hirsutum | | |
| Epilobium parviflorum | | |
|R Lythrum salicaria | | |
|R Peplis portula | | |
| Bryonia dioica | | |
| Cotyledon umbilicus | | |
| Saxifraga granulata | | |
| Saxifraga tridactylites | | |
|R Chrysosplenium alternifolium | | |
|R Chrysosplenium oppositifolium | | |
| Drosera rotundifolia | + | |
|A Myriophyllum spicatum | | |
|A Myriophyllum alternifolium | | |
|R Hydrocotyle vulgaris XII | ++ | |
|M Eryngium maritimum | | |
|R Cicuta virosa | ++ | |
|R Apium graveolens | | |
|R Apium nodiflorum | | |
|R Apium inundatum | | |
|R Sium latifolium | ++ | |
|R Sium angustifolium | ++ | |
|R Œnanthe crocata VI | ++ | |
|R Œnanthe phellandrium | + | |
| Æthusa cynapium | | |
|M Crithmum maritimum | ++ | |
|R Angelica sylvestris XII | ++ | |
|R Peucedanum palustre | ++ | |
| Pastinaca sativa | | |
| Chærophyllum sylvestre | | |
| Smyrnium olusatrum | | |
| Hedera helix | | |
| Viscum album | | |
| Sambucus nigra | | |
|R Galium palustre VI | ++ | |
| Galium mollugo | | |
| Galium aparine | | |
| Centranthus ruber | | |
| Valerianella olitoria | | |
| Eupatorium cannabinum | | |
|M Aster tripolium | | |
|R Bidens cernua VI | ++ | |
|R Bidens tripartita VI | ++ | |
| Chrysanthemum segetum | | |
| Chrysanthemum leucanthemum | | |
| Matricaria inodora | | |
|M Matricaria inodora, var. maritima | ++ | |
| Matricaria chamomilla | | |
| Achillea millefolium | | |
| Artemisia vulgaris | | |
| Artemisia absinthium | | |
| Tussilago farfara | | |
| Tussilago petasites | | |
| Senecio vulgaris | | |
|R Senecio aquaticus | | |
|R Senecio palustris | | |
| Carduus nutans | | |
| Carduus lanceolatus | | |
|R Carduus palustris | | |
| Carduus arvensis | | |
| Tragopogon pratensis | | |
| Tragopogon porrifolius | | |
| Tragopogon echioides | | |
| Leontodon autumnalis | | |
| Sonchus oleraceus | | |
| Taraxacum dens leonis | | |
| Crepis virens | | |
| Crepis fœtida | | |
| Lapsana communis | | |
|A Lobelia Dortmanna | | |
|R Hottonia palustris | | |
|R Lysimachia vulgaris | + | |
|R Lysimachia thyrsiflora | + | |
|M Glaux maritima | | |
| Anagallis arvensis | | |
|M Samolus valerandi | | |
| Pinguicula lusitanica | | |
| Ligustrum vulgare | | |
|R Menyanthes trifoliata | ++ | |
|R Limnanthemum nymphæoides | + | |
| Convolvulus arvensis | | |
| Convolvulus sepium XII | ++ | |
|M Convolvulus soldanella XII | ++ | |
| Cuscuta europæa | | |
| Lithospermum officinale | | |
|R Myosotis palustris | | |
| Myosotis arvensis | | |
| Myosotis versicolor | | |
| Lycopsis arvensis | | |
| Symphytum officinale | | |
| Borago officinalis | | |
| Datura stramonium | | |
| Solanum dulcamara | | |
| Solanum nigrum | | |
| Linaria vulgaris | | |
| Linaria cymbalaria | | |
| Scrophularia nodosa | | |
|R Scrophularia aquatica | | |
|R Veronica anagallis | | |
|R Veronica beccabunga | | |
| Veronica agrestis | | |
| Veronica arvensis | | |
| Bartsia odontites | | |
| Rhinanthus crista galli VI | ++ | Var. |
|R Pedicularis palustris | ++ | |
| Salvia verbenaca | | |
|R Lycopus europæus XII | ++ | |
|R Mentha aquatica VI | ++ | |
| Thymus sp. | | |
| Calamintha officinalis | | |
| Nepeta glechoma | | |
| Nepeta cataria | | |
| Prunella vulgaris | | |
|R Scutellaria galericulata XII | ++ | |
| Stachys betonica | | |
| Stachys sylvatica | | |
|R Stachys palustris | ++ | |
| Stachys arvensis | | |
| Galeopsis tetrahit | | |
| Ballota nigra | | |
| Lamium purpureum | | |
| Lamium album | | |
| Lamium galeobdolon | | |
| Teucrium scorodonia | | |
| Ajuga reptans | | |
| Verbena officinalis | | |
|M Armeria vulgaris | | |
| Plantago major | | |
| Plantago media | | |
| Plantago lanceolata | | |
|M Plantago maritima | | |
|M Salicornia herbacea | | |
|M Salsola kali | + | |
|M Suæda fruticosa | | |
|M Suæda maritima | | |
| Chenopodium album | | |
|M Beta maritima | | |
| Atriplex patula VI | ++ | |
|R Rumex aquaticus | + | |
| Rumex crispus | ++ | |
| Rumex obtusifolius | | |
|R Rumex hydrolapathum XII | ++ | |
|R Rumex conglomeratus XII | ++ | |
| Polygonum aviculare | | |
|M Polygonum maritimum | | |
| Polygonum convolvulus | | |
|R Polygonum amphibium | | |
|R Polygonum persicaria | | |
| Polygonum lapathifolium | | |
|R Polygonum hydropiper | | |
| Euphorbia helioscopia | | |
| Euphorbia segetalis | | |
|M Euphorbia paralias | ++ | |
| Euphorbia peplus (?) | | |
| Euphorbia amygdaloides | | |
|A Ceratophyllum demersum | | |
|A Callitriche aquatica | | |
| Urtica dioica | | |
| Ulmus campestris | | |
|R Alnus glutinosa XII | ++ | |
| Betula alba | | |
| Corylus avellana | + | |
| Quercus robur | + | |
| Pinus sylvestris | + | |
| Taxus baccata | | |
|R Typha latifolia | | |
|R Typha angustifolia | | |
|R Sparganium ramosum XII | ++ | |
|R Sparganium simplex VI | ++ | Var. |
|R Sparganium minimum | ++ | |
| Arum maculatum | | |
|R Calla palustris XII | ++ | |
|A Lemna minor | ++ | |
|A Lemna gibba | | |
|A Naias marina | | |
|A Zannichellia palustris | | |
|A Ruppia maritima | | |
|A Potamogeton natans XII | ++ | |
|A Potamogeton oblongus VI | ++ | |
|A Potamogeton lucens VI | ++ | |
|A Potamogeton perfoliatus | ++ | |
|A Potamogeton crispus | | |
|A Potamogeton densus | | |
|A Potamogeton obtusifolius | | |
|A Potamogeton pusillus | | |
|R Butomus umbellatus | | |
|R Sagittaria sagittifolia VI | ++ | Var. |
|R Alisma plantago VI | ++ | Var. |
|R Alisma ranunculoides | | |
|A Alisma natans | | |
|R Damasonium stellatum | | |
|R Scheuchzeria palustris | ++ | |
|R Triglochin palustre | | |
|R Triglochin maritimum | | |
|A Hydrocharis morsus ranæ | | |
|R Iris pseudacorus XII | ++ | |
| Iris fœtidissima | | |
| Tamus communis | | |
| Fritillaria meleagris | ++ | |
| Scilla nutans | | |
| Narthecium ossifragum | | |
|R Juncus communis | | |
| Juncus glaucus | | |
|R Juncus articulatus | | |
| Juncus squarrosus | | |
|R Juncus bufonius | | |
|M Juncus maritimus | | |
| Luzula campestris | | |
|R Cladium mariscus | ++ | |
|R Blysmus rufus | ++ | |
|R Scirpus palustris | | |
|A Scirpus fluitans | | |
| Scirpus setaceus | | |
| Scirpus holoschœnus | | |
|R Scirpus lacustris | | |
|M Scirpus maritimus | + | |
| Scirpus sylvaticus | | |
| Eriophorum alpinum | | |
| Eriophorum vaginatum | | |
| Eriophorum polystachion | | |
|R Carex leporina | ++ | |
| Carex stellulata XII | ++ | |
|R Carex canescens | ++ | |
| Carex remota XII | ++ | |
|R Carex paniculata XII | ++ | |
|R Carex vulpina XII | ++ | |
|R Carex acuta VI | ++ | |
| Carex hirta | | |
|R Carex flava VI | ++ | Var. |
| Carex distans | | |
| Carex panicea | | |
|R Carex pseudocyperus VI | ++ | |
|R Carex ampullacea | + | |
|R Carex paludosa XII | ++ | |
| Carex sp. | | |
| Carex sp. | | |
|R Leersia oryzoides | | |
|R Alopecurus geniculatus | | |
| Agrostis sp. | | |
| Agrostis sp. | | |
|R Poa aquatica | | |
|R Poa fluitans | | |
| Melica nutans | | |
|R Arundo phragmites | +? | |
+--------------------------------------+----+------+
Total of the original list: 320 species belonging to 192 genera and 65
families. Of these, about 260 were tested by the author, the data for
the remaining species being mainly derived from the writings of Thuret,
Kolpin-Ravn, and Sernander, with a few from those of Darwin and Martins.
NOTE.—Whilst this work has been going through the press, the author has
added thirteen species, seven genera, and two families to the list above
given; but the general inferences are not affected by the additions. The
corrected total would, therefore, be 333 species, 199 genera, and 67
families.
_On the effect of drying on the buoyancy of seeds and seed-vessels_
It has been already observed that this is as a rule but slight, and that
in the great majority of cases the effect of prolonged drying for many
months, or even for years, is at the most to give a seed or fruit
originally non-buoyant a floating power of a few days’ duration. This is
a subject to which I have paid especial attention in my experiments,
since, of course, much depends on it in the way of dispersal by
currents. It is obvious that a seed or fruit possessing impermeable
coverings at the time of its separation from the parent can scarcely be
compared with one where the coverings only attain their water-proof
capacity by drying. Most gardeners know that seeds which dry easily take
up moisture easily, and the principle applies in a varying degree to the
great majority of seeds and fruits.
Darwin was inclined to attach importance to adventitious buoyancy
acquired by drying; and in the _Origin of Species_ he refers to
instances offered by the fruits of the Hazel (Corylus), the Asparagus,
and Heliosciadium. In Note 48 I have referred to the cases of the Oak
and the Hazel; and, indeed, we have only to examine the beach-drift in
various parts of the world, and to look at their respective stations, to
learn that this is not an effective mode of dispersal. Buoyancy of seed
or fruit is only one of many other qualities that is concerned with
distribution by currents. Nature does not act in this way in
seed-distribution, and there can be little doubt that the author of the
_Origin of Species_ would have been the first to abandon this view, if
his researches had been continued. It should be especially noted that
plants of the sea-beach, where the floating power happens to be _nil_,
or limited only to a week or two, would have derived great advantage
from the drying of their seeds or fruits if it was really effective in
aiding dispersal by currents. However, with plants like Cakile maritima,
Eryngium maritimum, Glaucium luteum, &c., the effect of drying is very
small.
NOTE 11 (page 25)
THE EFFECT OF SEA-WATER IMMERSION ON THE GERMINATING CAPACITY OF SEEDS
AND SEED-VESSELS
Berkeley, Darwin, Martins, and others, long ago established the capacity
of seeds to germinate after prolonged immersion in sea-water. The reader
will find a _resumé_ of their results in the appendix to Mr Hemsley’s
volume on the _Botany of the Challenger Expedition_. The subject is well
illustrated in the original papers of those authors, and in my later
papers on the flora of Keeling Atoll, and on the seed-drift of the
Thames.
I may here remark that the earlier observers often pay more attention to
the retention of the germinating capacity after sea-water immersion than
to the degree of buoyancy. For this reason I have not been able to make
great use of the buoyancy results of Martins, since he frequently does
not distinguish between temporary and long-sustained buoyancy, an
objection also pointed out by Thuret and Hemsley.
NOTE 12 (page 27)
THE BUOYANCY OF THE FRUITS OF GALIUM APARINE
Norman and Sernander (see p. 172) attribute considerable buoyancy to
these fruits on account of the hollow cavity in each. I used to find
them in England in floating river-drift in autumn; and Norman observed
them on the Scandinavian beaches. They do not, however, float long, as
the cavity is open; and in two sets of my experiments they sank within a
few days.
NOTE 13 (page 29)
THE BUOYANCY OF THE SEEDS OF CONVOLVULUS SEPIUM
This plant seeded freely in 1893 in the Lower Thames Valley, as at
Molesey. I kept some of the seeds afloat for thirty-three months, of
which the first nine months were spent in sea-water and the rest in
fresh-water. One seed, at the end of the period, germinated healthily in
the fresh-water.
NOTE 14 (page 26)
OTHER LONG FLOTATION EXPERIMENTS
Whilst keeping my collections of Thames seed-drift in water from year to
year, I obtained a number of records of long “flotations.” Thus in
several cases, as with Bidens cernua and different species of Carex,
germination of the floating fruit took place in the water after a period
of two years. The same is also true of the seeds of Iris pseudacorus and
of the drupes of Sparganium ramosum. The last-named remained afloat in
the vessels, with the seed still sound, after four years; and the fruits
of Carex paludosa germinated afloat after three years in water. Many
drift fruits and seeds did not germinate freely in the vessels until the
second spring, that is, after a lapse of eighteen months; and in those
cases where the experiments were still further prolonged, a few
germinated in the vessels in the third and sometimes even in the fourth
year.
NOTE 15 (pages 33, 280)
THE OCCURRENCE INLAND OF SILENE MARITIMA
Prof. Schimper appeared to be in doubt as to the inclusion of this
littoral plant amongst those found in elevated mountain districts.
However, an interesting note on the occurrence of this plant on the
summit of one of the inland Norwegian mountains is given by Sernander
(p. 405), and is referred to by me on page 280 of this work.
NOTE 16 (page 34)
THE BUOYANCY OF THE SEEDS OR FRUITS OF THE BRITISH BEACH-PLANTS THAT
ALSO OCCUR INLAND
My experiments in the case of Armeria vulgaris, Artemisia, Cochlearia
officinalis, Plantago, the maritime forms of Spergularia rubra with and
without winged seeds, and Silene maritima disclose little or no floating
capacity even after prolonged drying. Thuret obtained similar results
for the Spergularia. It is unlikely that other plants of the group
possess any floating power worth speaking of. As indicated in Note 71,
the fruits of Raphanus maritimus float only for 7 to 10 days.
Nature disperses the fruits of Armeria vulgaris inclosed in the
persistent calyx; but in this condition they float only for 2 to 4 days
in sea-water, and the buoyancy of the capsule and seed is still more
limited. They are sufficiently light to be blown some distance by strong
winds, and the stiff hairs would cause them to adhere to a bird’s
plumage in the case of gulls nesting where the plants grow.
Reference to Matricaria inodora is made under Note 18.
NOTE 17 (page 35)
THE BUOYANCY OF THE SEEDS OR FRUITS OF THE GROUP OF BRITISH LITTORAL
PLANTS THAT FREQUENT SALT MARSHES AND MUDDY SHORES
_Aster tripolium._ The achenes, with or without the pappus, sink in
fresh and salt water in a day or two even after a year’s drying.
_Glaux maritima_ }
_Plantago maritima_ } The small seeds, or the seed-like nucules as
_Samolus valerandi_ } in Suæda, have but little floating power
_Suæda fruticosa_ } even after prolonged drying.
_Suæda maritima_ }
_Salicornia herbacea._ Would be dispersed probably by floating portions
of the plant, which, however, soon break down and the liberated seeds
sink. The floating seedling thrives in sea-water and could be carried
great distances (see Note 19).
_Salsola kali._ I experimented on this plant, both on the coast of
Devonshire and in Chile, with the same results in both localities
whether in the fresh state or after drying for weeks. The fruit sinks,
but when the plant dries the fruit is often detached inclosed in the
perianth, and floats in that condition in sea-water for a few days.
Portions of the plant of various sizes bearing mature fruits all sank
within ten days. It would seem at first sight, from the observations of
Prof. Martins, that the fruits float for several weeks; but his
experiments were mainly directed to testing the powers of germination
after sea-water _immersion_; and it is often not at all clear whether
_flotation_ is implied or even to be correctly inferred. There is a
slight suspicion of germination on the plant. Sea-birds doubtless aid in
the dispersion of this plant; the dry crisp portions of the plant
carrying fruits catch readily in one’s clothes on account of the
prickly-pointed leaves.
_Scirpus maritimus._ The fresh fruits float a few weeks in sea-water in
most cases, but 10 per cent. remain afloat after two months. After
drying for some months 30 per cent. remain floating after two months’
immersion.
} The fruits float a few days or a week. Drying
_Triglochin maritimum_ } somewhat increases the buoyancy. Sir W.
_Triglochin palustre_ } Buller in New Zealand found in the gullet
} of Anas superciliosa, the Grey Duck, numbers
} of the fruits of Triglochin triandrum.
NOTE 18 (page 35)
THE BUOYANCY OF THE SEEDS OR FRUITS OF THE BRITISH LITTORAL PLANTS THAT
ARE CONFINED TO THE BEACH
_Arenaria (Honckeneya) peploides._ The seeds float for many months in
sea-water unharmed, 75 per cent. floating after a year. They never
germinate in sea-water; but on being transferred to fresh water after
many months in sea-water they germinate healthily in a few days. These
seeds only float a few days in fresh water, all sinking within 10 days,
and even after a year’s drying they sink in a week or two. Precisely the
same results were produced in my experiments in 1892 on Cornish seeds,
and in 1904 on Devonshire seeds. In the great contrast between their
floating capacity in sea-water and in fresh water the seeds of this
plant defy the general rule that seeds that float a long time in
sea-water float also a long time in fresh-water. According also to
Sernander the seeds float a long time in the sea. He says that the
capsules float, but since they ultimately dehisce this could scarcely be
efficacious in dispersal. Floating portions of the plant also aid in its
dispersal, according to the same authority (p. 174). The plant forms
great extended masses on the pebbly shores of Spitzbergen (Ekstam, p.
28).
_Beta maritima._ Thuret found that the dried fruits of this plant
floated only two or three days in sea-water; whilst in my sea-water
experiments the freshly gathered fruits floated only one or two days.
Sernander speaks of them as fitted for dispersal from shore to shore;
but this could only be to a limited extent. Martins and Thuret
established by experiment the capacity of the germination of seeds of
other species of Beta after long immersion in sea-water; and the first
seems to imply that those of Beta vulgaris float for many weeks; but I
am inclined to think an error lies here.
_Cakile maritima._ The fruits, even after long drying, float, as a rule,
only a week and sink within ten days, the same results being afforded in
my sea-water experiments in 1893 on fruits from Cornwall, and in 1904 on
fruits from Devonshire. The fruits are common in the stranded drift on
the north coast of Devonshire and may often be seen germinating there.
They are also frequent in the beach drift of the Scandinavian coasts
(Sernander, p. 156).
_Crambe maritima._ The fruits were kept floating by Sernander more than
13 days (p. 165). Martins implies that they floated for 45 days. Darwin
says that they germinated after 37 days’ immersion in sea-water, but
does not specify that they floated all the time.
_Crithmum maritimum._ The ripe fruits readily separate into the two
carpels, which are very buoyant and float in sea-water for months. In my
experiments, 95 per cent. remained afloat after 10 months. It is
remarkable that whilst in sea-water the spongy covering of the carpels
retains its vitality, in fresh-water it becomes sickly and decays and
the carpels lose their floating power, so that they float weeks instead
of months as in the sea-water. The carpels are extremely light, being
washed up in the spray and blown up by the wind amongst the lightest of
the stranded drift of the Devonshire beaches. In a moderate gale they
are often blown off the beach and up the cliff-faces.
_Convolvulus soldanella._ From 40 to 50 per cent. of the seeds float
after six months in sea-water, and about 30 per cent. float after
eighteen months, retaining up to the end their germinating capacity.
Sernander implies that the plant is not found on the Scandinavian coast
to the north of Nissum Fjord in Denmark. It is known, however, to occur
in the south of Scotland. (I am indebted to Mr. Millett for his
extremely kind assistance in experimenting on this plant about ten years
since.)
_Eryngium maritimum._ The fruits float in sea-water, as a rule, only 3
or 4 days and all sink within a week. After drying for three months, the
floating period is only increased by a day or two. Though not at all
suited for transport for any distance by the currents, the carpels, on
account of their long prickly calyx teeth, would readily become
entangled in a bird’s plumage, and doubtless they are dispersed usually
in that fashion.
_Euphorbia paralias._ The seeds float a long time unharmed in the sea.
In my experiments at least 90 per cent. remained afloat after six weeks
in sea-water. On account of their small size they are liable to be
overlooked in beach drift; but they are to be found stranded on the
sands of our southern coasts, and they came under my notice in abundance
in the seed-drift of the Sicilian beaches.
_Glaucium luteum._—The seeds have no proper buoyancy even after
prolonged drying. On account of their oiliness they will float at first
on still water; but they can be made to sink at once or in a day by
dropping water upon them. The mode of dispersal is problematical.
_Lathyrus maritimus._—The seeds are evidently able to float a long time.
They were, according to Sernander (p. 178), found in quantities by J.
Schmidt cast up on some sand-islets near Falster in Denmark; and the
plant is regarded by Norman as distributed over the coasts of Arctic
Norway through the agency of the currents. They have, as observed by
Schmidt, considerable floating powers. Some small leguminous seeds,
seemingly of this species, which I found in the beach drift of
Woollacombe Sands, Devonshire, floated uninjured for many weeks in
sea-water.
_Matricaria maritima,_ maritime variety of M. inodora. The fruits
floated in my experiments unharmed after eight months in sea-water. In
an experiment made some years since on the fruits of the inland form I
noted that they had little or no buoyancy; but it is necessary to repeat
the observation. Sernander (p. 181) supports Norman’s view that these
plants are spread by the currents in Arctic Norway. The fruits occur in
the Baltic sea-drift and also in fresh-water drift. M. inodora is found
on sandy beaches in Nova Zembla. I am inclined to regard the maritime
form from the dispersal standpoint as a distinct species.
_Polygonum maritimum._—I have made observations on this plant in
Devonshire, the Lipari Islands, and the coast of Chile. As in the case
of several other species of Polygonum tested by me the fruits have
little or no buoyancy, but inclosed in the perianth they float three or
four days. The entire plant floats; but portions placed in sea-water
sank within five or six days. Shore-birds can alone explain the wide
distribution of this species.
The structural characters of some of these fruits or seeds are in their
relation to buoyancy discussed on page 115. It may be here observed that
the valuable results obtained by Prof. Martins in testing the
germinating capacity of the fruits and seeds of several of the
shore-plants above mentioned, after long immersion in sea-water, are at
times not to be depended on for the flotation indications, the
persistence of the seed’s vitality being the special purpose of his
research. His negative results as regards germination are not, however,
always conclusive, since the period employed from April to June was
quite insufficient. In many of my experiments seeds after long flotation
in sea-water did not germinate for a year or more afterwards. If his
investigation had been extended, the opinion that the Ranunculaceæ, the
Malvaceæ, and the Convolvulaceæ are apparently least able to resist the
action of sea-water would never have been formed. A very large amount of
evidence now shows that most seeds or fruits that are at all well
protected will germinate after long immersion in sea-water. But all
experiments must be well safeguarded and extended over a year or two.
The necessity of this was long since shown by Thuret. By employing
double sets of seeds he ascertained that in a third of the species
germination failed not only in the case of the seeds immersed in
sea-water, but also in those that had not been placed in sea-water at
all. Future investigators may, however, regard the buoyant qualities of
seeds or fruits with their associated structural characters as offering
now the true line of research. Observers beginning with Berkeley and
Darwin down to the present time have quite established the fact that
seeds as a rule germinate freely after long sea-water immersion.
NOTE 19 (page 35)
ON GERMINATION IN SEA-WATER
During my experiments on the buoyancy of about 270 British plants, about
a fourth of them (including most of those with buoyant seeds or fruits)
were subjected to prolonged immersion in sea-water from periods varying
from six to thirty-three months. If we except plants like Aster
tripolium, Salicornia herbacea, Triglochin maritimum, &c., that live
normally in salt marshes, or on the muddy banks of estuaries, only one
of the whole number, namely, Ranunculus sceleratus, displayed the
capacity of germination in sea-water. Amongst the plants that failed may
be mentioned the following that are confined to the sea-beach—Arenaria
peploides, Cakile maritima, Convolvulus soldanella, Eryngium maritimum,
Euphorbia paralias, Glaucium luteum, and we may here include Crithmum
maritimum of the rocky coasts. Of the beach-plants that also grow
inland, Silene maritima and Spergularia rubra (excepting the form found
on muddy coast flats) likewise failed. Amongst the plants of
miscellaneous inland stations that failed were Atriplex patula, Bidens
cernua, B. tripartita, Calla palustris, several species of Carex both
from dry and wet situations, Convolvulus arvensis, C. sepium,
Hydrocotyle vulgaris, Iris pseudacorus, several species of Juncus,
Lycopus europæus, Mentha aquatica, Ranunculus repens, Rhinanthus crista
galli, several species of Rumex, Scutellaria galericulata, Sparganium
ramosum, &c.
In nearly all the plants that failed to germinate in sea-water the
capacity of readily germinating in fresh water was displayed. The
restraining power of immersion in sea-water was illustrated over and
over again in my experiments. During the course of an experiment seeds
removed from the sea-water vessel and placed directly in a vessel of
fresh water kept beside the other germinated in a few days, whilst those
left in the sea-water never germinated, though often kept there for
months after. It was also noticeable that a previous sea-water immersion
favoured early germination in fresh water. It may be added that most of
the experiments were on floating seeds and seedvessels, though
germination also occurred in the sunken state.
It was ascertained in the exceptional case of Ranunculus sceleratus,
that although germination took place in sea-water, it was only after a
prolonged soaking of months had prepared the way. Of a number of its
seed-like fruits placed in fresh water and in sea-water in April and
kept under the same conditions, those in fresh water germinated freely
in a week or two, whilst those in sea-water did not begin to germinate
until the following October. Whilst the floating seedlings produced by
germination in fresh water grew vigorously and developed roots, those
resulting from germination in sea-water and left in the vessel only
attained a length of four millimetres in two months, developed no roots,
and showed only the first leaf. The sea-water seedlings were pale green,
and in their stout fleshy appearance contrasted greatly with the slender
fresh-water seedlings.
With regard to the germination in sea-water of the plants of the salt
marsh and of the mud-flats of estuaries, the following observations may
be made. With Aster tripolium the seeds germinate readily in sea-water
even when its density is raised by evaporation to 1·040; and I think
that by a carefully graduated series of experiments they could be
induced to germinate in brine. The seeds of Salicornia herbacea
germinate in sea-water more readily than in fresh water; and the
sea-water seedling is much the more vigorous and healthy of the two. I
kept the floating seedlings in sea-water for about ten weeks from the
date of germination, when they had developed the second joint and were
throwing out rootlets. After that, unless placed in salt-mud, they
became sickly and died. The floating seedling can evidently disperse the
species. I found with Spergularia marina, the maritime form of S. rubra,
that seeds of the plants growing on a sandy beach did not germinate in
sea-water, only those from plants growing on muddy coast-flats doing so.
But the sea-water seedlings, unlike those of Salicornia herbacea, but
like those of Ranunculus sceleratus, when left in sea-water did not
thrive. The seeds of Triglochin maritimum, as well as those of T.
palustre, behave very similarly in sea-water, germinating readily, the
liberated seedlings thriving afloat and producing the plumule. The
ultimate test of the capacity for germinating in sea-water seems to lie
in the behaviour of the seedling when left in the sea-water. Unless it
belongs to a characteristic plant of the salt marsh or of the estuary,
like Salicornia, it makes but little attempt at growth whilst afloat in
sea-water, showing no rootlets, though at times developing the plumule.
The germination of seeds in sea-water also attracted the notice of
Darwin; but his results in some respects are scarcely those I should
have looked for (_Gardener’s Chronicle_, May, 1855, and _Journ. Linn.
Soc._, vol. i., p. 130, 1857). Out of the seeds of 87 plants placed in
sea-water to test their capacity of germination when afterwards planted,
in three cases, those of Tussilago farfara, Convolvulus tricolor, and
the garden Orache (Atriplex), the seeds germinated under the water, the
freed seedlings, as with the two first named plants, living in the
sea-water for some time after. Darwin was evidently himself surprised at
these results, and I am quite unable to understand them. In England and
in the tropics I have carried on prolonged sea-water experiments on the
seeds of at least fifteen species of Convolvulus and Ipomœa (including
the beach plants C. soldanella and I. pes capræ) and have never obtained
such a result. The seeds will nearly always germinate well in fresh
water; but in sea-water the process begins, as indicated by the swollen
seed, and then aborts, the embryo dying (see page 83). The seeds of
Atriplex patula, though a long time in sea-water in my experiments, made
no attempt to germinate there. Neither Prof. Martins, who experimented
upon the effects of sea-water immersion on the seeds of nearly 100
plants, including many coast species, nor M. Thuret, who experimented in
sea-water on the seeds of 251 plants, the experiments being in some
cases prolonged for more than a year, make any reference, as far as I
could gather from their writings, to any cases of germination in
sea-water. Darwin’s results, however, are always significant in matters
of dispersal; and perhaps one of my readers will be able to experiment
again on his three plants.
When in Hawaii, I made some observations on the germination of Batis
maritima in sea-water, a plan with which I was also familiar in its home
in the salt-water pools of the coast of Peru. The mature fruits, on
being freed from the parent plant in sea-water, float away, and in from
one to two weeks they break down from decay, setting free the seeds. The
seeds float in sea-water indefinitely, their buoyancy only terminating
with their germination, the first seeds germinating afloat about six
weeks after the breaking down of the fruit, whilst the rest continue to
float in the sea-water during the next three months, some of them
germinating at intervals, and all of them doing so eventually. Strange
to say, although the seedlings remained healthy whilst afloat in the
sea-water, they made no effort either to separate the cotyledons or to
produce a plumule.
NOTE 20 (page 42).
ON THE MAXIMUM HEIGHTS REACHED BY SOME SHORE PLANTS IN THEIR EXTENSION
INLAND IN VANUA LEVU, FIJI
Since they occupy the “talasinga” districts described in the following
note, these shore plants would be expected to extend as high as those
districts extend, namely, to about 1,500 feet above the sea. This indeed
represents their limit excepting in one instance; but many fall
considerably short of this elevation.
_Canavalia obtusifolia_, variety, 700 feet, rare.
_Cassytha filiformis_, 950 feet.
_Cerbera Odollam_, 1,200 feet: 2,600 feet in one exceptional case on
the slopes of Mbatini.
_Colubrina asiatica_, 400 feet.
_Cycas circinalis_, 1,100 feet.
_Derris uliginosa_, 1,000 feet, rare.
_Ipomœa pes capræ_, 1,300 feet.
_Morinda citrifolia_, 700 feet.
_Scævola Kœnigii_, not common inland, and rarely over 100 feet above
the sea; but it may occur miles from the beach, as near Vatu Levoni,
where a few stunted plants were growing five miles from the coast.
_Vitex trifolia_, 1,300 feet, usually more or less unifoliolate and
procumbent.
Unless otherwise stated all the plants above named are common inland, as
also are _Premna tahitensis_, _Tacca pinnatifida_, _Tephrosia
piscatoria_, _Hibiscus tiliaceus_, &c.; but I have made no note of
_Thespesia populnea_ occurring far off the beach.
NOTE 21 (pages 42, 43)
ON THE DWARFING OF SHORE PLANTS WHEN EXTENDING INLAND INTO THE
“TALASINGA” PLAINS IN VANUA LEVU.
_Premna tahitensis_, 9 or 10 feet high at the coast, may here be only 3
feet high. Other trees like _Morinda citrifolia_ become also stunted.
_Cerbera Odollam_, a moderate-sized tree at the coast, may in the
“talasinga” plains be only 4 to 6 feet high, but it here displays
distinct varietal characters. Whilst the shore trees of Cerbera Odollam
have broad leaves (length 3 times the breadth) with obtuse points, and
short, stout flower-peduncles (1-1/2 - 2 inches), the inland or
“talasinga” species has long lanceolate leaves (length 7 or 8 times the
breadth), and long, slender flower peduncles (3 inches). However,
intermediate forms are common, the broad-leaved coast tree approaching
the inland plant and _vice versâ_.
NOTE 22 (page 43)
THE “TALASINGA” PLAINS OF VANUA LEVU, FIJI
Amongst the most conspicuous features of the north and north-west or lee
sides of the large islands of Vanua Levu and Viti Levu are the extensive
rolling plains that extend from the sea-border for some miles inland to
the foot of the mountains. It is to those of the first-named island that
the following remarks strictly apply; but no doubt they will serve
equally well for those of the other island. In the first volume on the
geology of Vanua Levu, reference is frequently made to this subject, and
the reader may profitably look at the remarks there made.
Here the mountain-forests more or less abruptly cease, and we have an
undulating region of grass, reeds, and ferns dotted over with
Casuarinas, Pandanus trees, Cycads, Acacias, and shrubby growths. Though
the list of plants characteristic of these plains is not small, they are
not, as a rule, numerous in any one locality, and the general appearance
is one of aridity. A dry, crumbling soil, often deeply stained by
iron-oxide, is plentifully exposed; and blocks of basic volcanic rocks
in all stages of disintegration are strewn over the surface in many
localities. Rivers, fed by the heavy rainfall of the forested slopes of
the mountains, traverse these regions, but, as a rule, receive no
tributaries; and the districts have, in fact, well earned the name given
to them by the natives of the “talasinga,” or sun-burnt, lands.
The vegetation, though sparse and scanty in comparison with that of the
forests, is sufficiently varied when it comes to be more closely
examined. In one locality we may have extensive tracts covered with
Gleichenia, Pteris, and other ferns of the bracken habit. In another,
tall reeds (Eulalia) and grasses cover large areas. Here, more than one
species of Tacca (T. pinnatifida and T. maculata) thrive. There, the
Turmeric (Curcuma longa) abounds. Trailing over the soil in one place we
notice Ipomœa pes capræ, in another the Yaka (Pachyrrhizus trilobus),
and in another the procumbent unifoliolate form of Vitex trifolia.
Amongst the shrubs and small trees we observe in different localities
the Sama (Commersonia echinata), the Mbulei (Alstonia plumosa—one of the
rubber plants), Mussænda frondosa, Melastoma denticulatum, and Nelitris
vitiensis, the Nunga-nunga. Dodonæa viscosa, found in similar regions in
Australia and New Zealand, abounds in places; and here and there may be
seen species of Hibbertia, another Australian genus. Fagræa Berteriana,
the Mbua tree, grows abundantly in certain districts, as in the Mbua
plains, and Gardenias are at times abundant. One or two characteristic
beach-plants have been already mentioned, and amongst others
particularly frequent in these plains are Cassytha filiformis, Cerbera
Odollam, Morinda citrifolia, and Premna tahitensis.
When these talasinga districts approach the forests, patches of wood
occur at intervals, and we observe here the Candle-nut Tree (Aleurites
moluccana), the Vunga (Metrosideros polymorpha), and the Thau-kuro
(Casuarina nodiflora). Such are some of the botanical features of these
districts; but the reader will acquire a sufficiently correct general
notion of the floral physiognomy of these regions if he bears in mind
their most conspicuous characters, those of an undulating region more or
less covered with ferns, tall reeds, and grass, and dotted over, either
separately or in clumps, with Casuarinas (C. equisetifolia), Screw-pines
(Pandanus odoratissimus), Cycads (C. circinalis), and Acacias (A.
Richii, &c.).
However, the peculiar vegetation of these plains often ascends the lower
slopes of the mountains, reaching to various elevations. In Vanua Levu
it often ceases at 900 or 1,000 feet, but it may only reach to 400 or
500 feet, and, on the other hand, not uncommonly it ascends to as much
as 1,500 feet, the greatest elevation recorded by me being 1,600-1,700
feet in the Sealevu district. It extends miles inland, and where
conditions are suitable it may reach the heart of the island.
Different explanations have been offered of the origin of the peculiar
vegetation of the leeward slopes of these islands. It is, however, a
phenomenon that is presented over much of the globe by islands lying in
the track of regular winds, the weather, or wet, side being densely
wooded, whilst the lee, or dry, side is covered with grass, ferns, and
similar vegetation. The predisposing cause must be climatic; and
although Mr. Horne’s explanation attributing it to the effect of fires
and to a faulty system of native cultivation (pp. 80, 132) may be
doubtless true in certain localities, the influences at work here must
be the same as are at work in other islands and on continental coasts in
other parts of the world.