THE ARAUCARIA FAMILY
'And so the grandeur of the Forest-tree
Comes not by casting in a formal mould,
But from its own divine vitality.'
Wordsworth.
As an additional illustration of existing cone-bearing trees which form
links with the past we may briefly consider the genera Araucaria and
Agathis, the two members of the family Araucarieae. It is generally
agreed that the branches of the genealogical tree of this family
extended farther back into the past than in the case of the majority
of Conifers. By some authors the surviving representatives of the
Araucarian stock are considered to have a strong claim to be regarded
as the most primitive as well as the oldest of cone-bearing trees,
though this opinion, like many others, is not held by botanists as
a whole. This is not the place to discuss matters of controversy,
and I shall confine myself to a general consideration of Araucaria
and Agathis from the point of view of their present distribution
and the part they played in the vegetation of the Mesozoic and
Tertiary epochs. In 1741 a plant from Amboyna, one of the Moluccas,
was described under the name _Dammara alba_. For this tree, known
as the Amboyna Fine, the English botanist Salisbury instituted the
generic name Agathis, from a Greek word (αγαθις) meaning a ball of
string and probably suggested by the form of the cones, which is the
designation usually adopted in botanical literature instead of the
pre-Linnean term Dammara. The best known species of the genus is the
Kauri Pine, probably the finest forest tree in New Zealand where it
still flourishes from the North Cape to latitude 38° S., though the
occurrence of sub-fossil trunks and pieces of buried resin shows that
the Kauri forests are gradually dwindling. The stems of this species,
_Agathis australis_, rise like massive grey columns to a height of 160
ft., terminating in a succession of spreading branches given off in
tiers from the main trunk. The thick narrow lanceolate leaves, with
several parallel veins, reach a length of 2 to 3 inches. The female
shoots have the form of small and almost spherical cones consisting of
a central axis bearing overlapping spiral series of broadly triangular
scales (Fig. 16). Each scale carries a single seed with a large
wing attached to one side which facilitates disposal by wind. Other
species of Agathis occur in the Malay Archipelago, the Philippines,
in Queensland, in the New Hebrides, New Caledonia, the Fiji Islands,
and elsewhere. With the exception of the Australian Kauri (_Agathis
robusta_), with leaves larger and broader than those of the New Zealand
Kauri, the genus is essentially an island type. With the exception of
some species of the southern hemisphere genus Podocarpus, there are no
Conifers with foliage like that of Agathis. It is, however, the broad
and thin single-seeded scales and the spherical cones, in some species
six inches in length, which furnish the most trustworthy means of
identifying the genus.
[Illustration: Fig. 16. A. _Agathis robusta_ Muell. (much reduced). B.
_Agathis Moorei_ Lind. (1/2 nat. size).]
[Illustration: Fig. 17. _Araucaria excelsa._ The upper part of a small
tree in the Cambridge Botanic Garden. (Much reduced.)]
The allied genus Araucaria, with the exception of two South American
species, the familiar Monkey Puzzle, _Araucaria imbricata_, and
a Brazilian tree, _Araucaria brasiliana_, is confined within the
geographical area occupied by Agathis. The name Araucaria was first
used by de Jussieu in 1789 for a plant previously referred to the
genus Pinus and described as one of the most beautiful trees of Chili.
This species, _A. imbricata_, introduced into England in 1796, grows
on the southern slopes of the Andes and, as in the case of the Kauri
forests of New Zealand, buried stems point to a wider extension of
the forests in earlier days. The sharp and thick leaves of the Monkey
Puzzle distinguish it from all other Conifers; its large almost
spherical seed-bearing cones, more than half a foot in length, which
may occasionally be seen on well-grown British trees, are unlike those
of other genera. Each of the deep and narrow scales bears a single
seed embedded in the substance of the scale and terminates distally
in a narrow upturned process. Some species of Araucaria, differing
considerably in the form of the leaves and in the shape and structure
of the seed-scales from the Chilian species, are conveniently placed
in a distinct sub-division of the genus Araucaria. Of this type the
Norfolk Island Pine, _Araucaria excelsa_, is the best-known example
(Fig. 17). It was introduced to Kew by Sir Joseph Banks in 1793, soon
after its discovery by Captain Cook, who describes the stems of the
Norfolk Island trees as resembling basaltic columns, and relates how on
approaching the island everyone was satisfied that the columnar objects
were trees, 'except our Philosophers, who still maintained they were
basaltes.' The leaves are short, about half an inch long, laterally
compressed and slightly spreading and sickle-shaped--sometimes shorter
and broader and overlapping--arranged in crowded spirals. The scales
of the broadly oval cones are single-seeded, but differ from those
of _Araucaria imbricata_ in having the seed exposed on the surface
and in the greater breadth and thinner borders of the scales. In both
Araucaria and Agathis the nature of the seed-scales constitutes a
distinguishing feature. The leaves of _Araucaria imbricata_ differ in
form from those of other Conifers. The foliage shoots of _Araucaria
excelsa_ and other species, _e.g._ the very closely allied _A. Cookii_
of the New Hebrides and New Caledonia, though not unlike the branches
of a Japanese Conifer (_Cryptomeria japonica_), often cultivated in
England, afford fairly trustworthy characters for identification
purposes.
The minute structure of the wood of both Araucaria and Agathis
constitutes an important distinguishing feature and enables us to
recognise on microscopical examination even a fragment of wood of
either of these genera. The small elongated cells or water-conducting
elements of the wood of the Araucarieae are characterised by one or
two, and occasionally as many as three or four, contiguous rows
of pits on their radial walls, and these appear in surface view as
flattened circles or polygonal areas.
These details have been mentioned in order to show that Araucaria and
Agathis are sufficiently distinct in many respects from other Conifers
to render their identification in a fossil state comparatively easy, at
least much easier than the recognition of the majority of the members
of the Coniferae. It would be going too far to state definitely that
Araucarieae, as defined by reference to existing species, existed
during the Palaeozoic period; on the other hand it would seem in a
high degree probable that the vegetation of the Coal age and of the
succeeding Permian period included trees in which certain Araucarian
characters were clearly foreshadowed. The name Araucarioxylon was
formerly applied to petrified wood, obtained from Palaeozoic as well
as from later formations, which agrees anatomically with that of
Araucaria and Agathis. It has been shown in recent years that much of
the Palaeozoic wood of this type of structure belongs to the extinct
genus Cordaites, a tree which played a prominent part in the earlier
floras. Cordaites affords a good example of a generalised type: in its
wood-structure it resembles very closely the existing Araucarieae;
its long strap-like leaves are not unlike those of some species of
Agathis; its male flowers have often been compared with those of the
Maiden Hair tree, _Ginkgo biloba_, and certain anatomical features form
connecting links between this Palaeozoic genus and the Cycads.
It is noteworthy that in another Palaeozoic genus, Walchia, the
leaf-bearing branches are identical in appearance with those of the
Norfolk Island Pine (Fig. 17) and some other species of Araucaria.
Unfortunately our knowledge of the reproductive organs of Walchia is
insufficient to warrant any definite statement as to the degree of
consanguinity between this Permian and Upper Carboniferous plant and
the Araucarieae; it is probable that in Walchia we have a type not far
removed from the line of evolution which led to Araucaria. Petrified
wood, identified as that of Walchia, and exhibiting the Araucarian type
of structure, has been recorded from Permian rocks of the Vosges. Other
instances might be quoted in support of the view that the Palaeozoic
floras included a few plants with which the surviving Araucarieae may
fairly claim relationship. Professor Zeiller of Paris has recently
described some fossil shoots from Palaeozoic rocks in India under the
name _Araucarites Oldhami_ on the ground of the similarity of the
leaves to those of _Araucaria imbricata_. Similarly, from Triassic
rocks several fossils have been described as closely allied to
Araucaria, in some cases because of anatomical resemblances and in
others on the less satisfactory evidence furnished by a similarity in
the foliage shoots. Professor Jeffrey of Harvard has recently given an
account of a new type of stem (Woodworthia) from the petrified Triassic
forest of Arizona possessing some Araucarian characters, though
differing from existing species of Araucaria in certain structural
features, a combination of characters regarded by this Author as an
indication of relationship with the family of Conifers, which includes
the Pines, Firs, Larches and other well-known northern genera.
It is, however, from the records of Jurassic rocks that we obtain
the most satisfactory information as to the great antiquity and the
very wide geographical range of the ancestors of the recent genus.
The plant-beds of the Yorkshire coast afford clear evidence of the
occurrence of Araucarian trees in the woodlands of the Jurassic
period. Petrified wood has been found at Whitby, associated with jet,
showing the minute structural characteristics of the surviving species
of Araucarieae, and it is not improbable that some at least of the
Whitby jet has been formed from the wood of Araucarian plants. The
carbonised remains of leafy shoots preserved in the Jurassic shales
near Scarborough and on other parts of the Yorkshire coast include
twigs hardly distinguishable from those of _Araucaria excelsa_, though
the resemblance of external form alone, especially in the case of
foliage shoots, does not amount to proof of generic identity. We have,
however, the much more trustworthy evidence of cones and seed-bearing
scales in which the characteristic features of living species are
clearly shown. Seed-bearing scales almost identical with those of
_Araucaria excelsa_ and other recent species have long been known from
the Jurassic rocks of Yorkshire.
From other parts of England where samples of Jurassic floras are
preserved, as at Stonesfield in Oxfordshire, in Northamptonshire and
elsewhere, equally striking examples of undoubted Araucarias have been
found.
Fig. 18 represents part of a large cone described in 1866 by Mr
Carruthers from Jurassic rocks at Bruton in Somersetshire: this
specimen, now in the British Museum, consists of one side of a
spherical cone about 5 inches long and 5 inches broad; in size, as in
the form of the seed-scales, it shows a striking likeness to the cones
of the Australian species _Araucaria Bidwillii_, the Bunya Bunya of
Queensland. Other equally convincing examples of Jurassic Araucarian
cones and seeds may be seen in the museums of York and Northampton. On
the north-east coast of Sutherland there is a narrow strip of Jurassic
beds forming a low platform between the granitic and Old Red Sandstone
hills and the sea. From these rocks Hugh Miller described several
fossil plants in his _Testimony of the Rocks_, and an examination of a
large collection obtained from this district by the late Dr Marcus Gunn
shows that Miller was justified in speaking of Araucaria as a member of
this northern flora.
[Illustration: Fig. 18. _Araucarites sphaerocarpus_ Carr. From Jurassic
rocks at Bruton, Somersetshire. (British Museum, 2/3 nat. size.)]
There is abundant evidence pointing to the existence in Britain during
the Jurassic period, and in the early days of the Cretaceous epoch, of
Araucarian trees which differed but slightly from the modern species
confined to the southern hemisphere. In several localities in France,
Germany, and other parts of the continent, Araucarian fossils have
been recognised in Jurassic rocks. It is almost certain that some
foliage shoots and imperfectly preserved cones described by Dr Nathorst
from Upper Jurassic rocks in Spitzbergen were borne by a species of
Araucaria. Cone-scales very similar to those from Yorkshire have been
discovered in Wealden beds in Cape Colony, and Araucarian wood of
Jurassic and Cretaceous age has been found in Madagascar. From Jurassic
strata in India and Victoria (Australia), as well as from Upper
Jurassic and Lower Cretaceous rocks in Virginia and elsewhere in the
eastern United States, well preserved Araucarian fossils are recorded.
In a collection of Jurassic plants, obtained a few years ago by the
members of a Swedish Antarctic Expedition in Graham's Land, Dr Nathorst
has recognised some cone-scales of Araucaria, which demonstrate a
former extension of the family beyond the southern limits of South
America.
It is interesting to find that when we ascend higher in the
geological series and pass beyond the Wealden strata to the Middle
and Upper sub-divisions of the Cretaceous period, evidence of the
wide geographical distribution of the Araucarieae is still abundant.
Araucarian wood has been obtained in rocks classed as Upper Cretaceous
in Egypt, in East Africa, in Dakota, and elsewhere. In the sedimentary
rocks of the Tertiary period undoubted examples of Araucaria are less
common, though there can be no doubt that the genus was much more
widely spread then than it is at the present day. The well-known
Tertiary plant-beds of Bournemouth have afforded specimens of foliage
shoots which have been described as a species of Araucaria, though in
the absence of well-preserved cones or petrified wood we must admit
that the data are inconclusive. It is, however, legitimate to regard
the striking similarity of the Bournemouth twigs to those of _Araucaria
excelsa_ and _A. Cookii_ as constituting a fairly strong case in
favour of the persistence of Araucaria in Western Europe up to the
earlier stage of the Tertiary period. Araucarian wood of Tertiary age
is recorded from India, while branches with broad leaves like those
of _Araucaria imbricata_ have been found in Seymour Island and the
Magellan Straits, and specimens of Tertiary wood are described from
Patagonia. At the other end of the world. Tertiary rocks on the west
coast of Greenland have yielded fragments which may be referred with
some hesitation to the genus Araucaria.
A few words must be added in regard to the recent discovery by
Professor Jeffrey and Dr Hollick of some very interesting Cretaceous
specimens in New Jersey of well-preserved cone-scales and foliage
shoots of extinct plants closely related to the existing species of
Agathis(51). The American fossils are particularly valuable because
their preservation admits of microscopical examination of the tissues.
In Cretaceous rocks of Staten Island and in other localities on the
eastern border of the northern United States, kite-shaped seed-bearing
scales almost identical in form with those of recent species of Agathis
are fairly common fossils. Similar specimens have long been known
from Tertiary rocks in western Greenland. In the case of some of the
American examples each scale bore three seeds instead of a single seed
in living species: on account of this difference Prof. Jeffrey and Dr
Hollick have adopted a distinct generic name, _Protodammara_.
The foregoing sketch is necessarily far from complete, but it may serve
as an illustration of the light which is thrown on the past history of
recent plants by the investigation of the relics of ancient floras.
The family Araucarieae now represented by a small number of species
which, with the exception of the Andian and Brazilian Araucarias, are
restricted to a small region in the southern hemisphere, was one of
the most widely spread sections of the seed-bearing plants during the
Mesozoic era. Ancestors of Araucaria must have been common trees in the
European vegetation in Jurassic and Lower Cretaceous periods, and even
as late as the Tertiary period there is evidence that representatives
of the family still lingered in the north. One conclusion which seems
almost unavoidable is that the species of Araucaria and Agathis that
survive, in some cases only in one or two small islands in the South
Pacific, have in the course of successive ages wandered from the other
end of the world. Their migrations can be partially traced by the
fragments embedded in Jurassic and later sediments, but we can only
speculate as to the causes which have contributed to the changes in the
fortunes of the family; how much influence may have been exerted by
changes in physical conditions in the environment, and to what extent
the production of more successful types may have been the dominant
cause of the decline, it is impossible to say. One thing at least is
certain, that few existing plants are better entitled to veneration as
survivals from the past than are the living species of Araucaria.