THE REDWOOD AND MAMMOTH TREES OF CALIFORNIA
'Your sense is sealed, or you should hear them tell
The tale of their dim life, with all
Its compost of experience....'
W. E. Henley.
Since their introduction into England about the middle of the
nineteenth century, the two Californian species _Sequoia sempervirens_
(the Redwood) and _Sequoia gigantea_ (the Mammoth tree) have become
familiar as cultivated trees. The name Sequoia, said to be taken
from Sequoiah, the inventor of the Cherokee alphabet, was instituted
in 1847, while the name Wellingtonia, often used in horticulture
though discarded by botanists in favour of the older designation
Sequoia, was proposed in 1853. Both species are now confined to a
comparatively small area in California: their restricted geographical
range, considered as an isolated fact, might be regarded as a sign of
recent origin. The records of the rocks, however, afford ample proof
that rarity in this as in many other instances is the precursor of
extinction. The famous groves of Mariposa and Calaveras represent the
last resting-place of giant survivors of a race which formerly held its
own in Europe and in other parts of the world.
The Redwood, _Sequoia sempervirens_, occupies a narrow belt of country,
rarely more than 20 or 30 miles from the coast, three hundred miles
long from Monterey in the south to the frontiers of Oregon; it has
a stronger hold on existence than Sequoia gigantea. In Northern
California it still forms pure forests on the sides of ravines and on
the banks of streams. The tapering trunk, rising from a broad base to
over 300 ft., gives off short horizontal branches thickly set with
narrow spirally disposed leaves 1/4-1/2 inch in length arranged in
two ranks like the similar leaves of the Yew. The lower edge of each
leaf is decurrent, that is it runs a short distance down the axis of
the branch instead of terminating at the point of attachment. It is by
paying attention to such details as this as well as to more important
features, that we are able to connect fragmentary fossil twigs with
those of existing species. The female 'flowers' have the form of oblong
cones from 3/4 to 1 inch long: each consists of a central axis bearing
crowded wedge-shaped, woody appendages or cone-scales, which gradually
increase in breadth towards the exposed distal end characterised by its
four sloping sides and by a median transverse groove. Several small
seeds are borne on the upper surface of the cone-scales. The smaller
and short-lived male flowers need not be described.
[Illustration: Fig. 13, _Sequoia gigantea._ King's Co., California.
(From Prof. D. H. Campbell)]
The other and better known species _Sequoia gigantea_ (Fig. 13) has an
even more restricted range and is confined to groves on the western
slopes of the Sierra Nevada between 3000 to 9000 ft. above sea-level.
This tree is at once distinguished from the Redwood by its ovate,
sharply pointed and stiffer leaves which retain their spiral
disposition and closely surround the axis of the twigs like
obliquely-set needles. The cones are of the same type as those of
_Sequoia sempervirens_, but are broader and may attain a length of
3-1/2 inches (9·5 cm.) (Fig. 14).
Reference has already been made to Sequoia as a striking illustration
of longevity. It is also selected as an equally impressive example of
a type verging on extinction, which played a prominent part in the
vegetation of both west and east during the Cretaceous and Tertiary
periods.
[Illustration: Fig. 14. _Sequoia gigantea_ Torr. (7/8 nat. size.)]
Scraps of branches with leaves hardly distinguishable from those of
the existing Californian trees are frequently met with in Tertiary
and Mesozoic sediments, and with them occasionally occur cones too
imperfectly preserved to afford satisfactory evidence of more than
superficial agreement with those of the recent species. The task of
deciphering the past history of plants, particularly of the Conifers,
is accompanied by many difficulties and insidious temptations. It is
clear from a critical examination of many of the recorded instances
of fossil Sequoias that the generic name has been frequently used
by writers without adequate grounds. The fragmentary specimens
available to the botanical historian cannot as a rule be subjected
to microscopical investigation, and even a partial acquaintance with
the similarity of the foliage of different types of living Conifers
is sufficient to convince the student of the need of self-control in
the identification of the fossils. It is, however, easy to point out
obvious pitfalls, though difficult to maintain a judicial attitude in
the excitement of endeavouring to interpret documents which are too
incomplete to be identified with certainty. If we put on one side all
records of supposed fossil Sequoias not based on satisfactory data,
there remains a wealth of material testifying to the antiquity of the
surviving species.
It is by no means improbable that Conifers closely allied to the
Redwoods and Mammoth trees of California were represented in Jurassic
floras; but hitherto no proof has been obtained of the occurrence of
a Sequoia among the rich material afforded by the Jurassic plant-beds
of Yorkshire and by beds of the same age in other countries. A small
cone has recently been described from strata near Boulogne belonging
to the latest phase of the Jurassic period, which presents a strong
resemblance in shape and size and in the form of the cone-scales to
those of the recent species. This specimen, though not conclusive,
is the most satisfactory indication of a Jurassic Sequoia so far
discovered. From Lower Jurassic rocks in Madagascar similar cones
have been recorded in association with foliage-shoots like those of
_Sequoia gigantea_, but here too the evidence is not beyond suspicion.
In plant-bearing strata of Wealden age, such as are exposed in the
cliff near Hastings and in deposits of the same age in North Germany,
Portugal, and elsewhere, twigs and cones have been found which may be
those of trees nearly allied to the genus Sequoia.
[Illustration: Fig. 15. _Sequoia Couttsiae_ Heer. Twigs (A) and
cone-scales (B) from Bovey Tracey. (× 3.) (Photographs by Mr and Mrs
Clement Reid.)]
It is, however, in the sedimentary rocks of Cretaceous age, rather
higher in the series than those in the Hastings cliffs, and in the
succeeding Tertiary rocks, that undoubted Sequoias are met with in
abundance. At Bovey Tracey in Devonshire there is a basin-shaped
depression in the granitic rocks of Dartmoor filled with clay, gravel
and sand--the flood-deposits of a Tertiary lake containing waifs
and strays of the vegetation on the surrounding hills. Among the
commonest plants is one to which the late Oswald Heer gave the name
_Sequoia Couttsiae_, and his reference of the specimens to the genus
Sequoia has been confirmed by the recent researches of Air and Mrs
Clement Reid(50). This Tertiary (Oligocene) species is represented by
slender twigs almost identical with those of _Sequoia gigantea_ and by
well-preserved cone-scales and seeds (Fig. 15). Moreover, it has been
possible to examine microscopically the structure of the carbonised
outer skin of the leaves and to demonstrate its agreement with that
of the superficial tissue in the leaves of the Mammoth tree. With the
Bovey Tracey Sequoia are associated fragments of Magnolia, Vitis, and
_Taxodium distichum_, the swamp Cypress of North America, together
with other types which have long ceased to exist in Western Europe.
Other British examples of Sequoia have been described from Tertiary
beds at Bournemouth, the Isle of Wight, Sheppey, and Antrim, but the
material from these localities is inferior in preservation and cannot
be identified with the same degree of certainty as in the case of the
Devonshire specimens. The occurrence of twigs and cones of several
species of Sequoia in both Cretaceous and Tertiary rocks in Austria,
Germany, Italy, France, and elsewhere, shows that the ancestors of the
Californian trees were common in the European region.
The exploration of Cretaceous and Tertiary rocks in Arctic Europe
has revealed the former existence in Greenland, Spitzbergen, and
other more or less ice-covered lands of plants which clearly denote
a mild climate. Cones and branches of Sequoias have been found in
abundance in Lower Tertiary beds on Disco Island off the west coast
of Greenland, and similar evidence of the northern extension of the
genus has been obtained from Spitzbergen. Dr Nathorst of Stockholm
speaks of twigs of Sequoia in the Tertiary clays of Ellesmere Land
almost as perfect as herbarium specimens. In Tertiary beds on the banks
of the Mackenzie River, in Alaska, Saghalien Island and Vancouver
Island, and in Upper Cretaceous rocks in the Queen Charlotte Islands,
remains of Sequoia have been discovered. One of the most remarkable
instances of the preservation of trees of a bygone age is supplied
by the volcanic deposits of Lower Tertiary age exposed on the slopes
of Amethyst mountain in the Yellowstone Park district. At different
levels in the volcanic and sedimentary material, which is piled up to
a height of over 2000 ft. above the valley, as many as fifteen forests
are represented by erect and prostrate limbs of petrified trees (Fig.
6). The microscopical examination of some of these trees has shown
that they bear a striking resemblance to _Sequoia sempervirens_. In a
photograph of these petrified forests by the U.S. Geological Survey
(36, 2) one sees living Conifers side by side with the lichen-covered
and weathered trunks of the fossil species (_Sequoia magnifica_),
living and extinct being at a distance hardly distinguishable.
(Frontispiece.)
In concluding this brief survey of the fossil records of Sequoia,
reference may be made to the discovery of petrified wood in Cretaceous
rocks in South Nevada, possessing the anatomical features of _Sequoia
gigantea_, which shows that close to the present home of the big trees
their ancestors flourished during a period of the earth's history too
remote to be measured by human reckoning.
The distribution of the Tertiary and Cretaceous Sequoias would appear
to have been mainly in the northern hemisphere, extending well within
the Arctic circle. It is, however, by no means improbable that the
ancestors of Sequoia flourished far south of the equator. Reference has
been made to Jurassic fossils from Madagascar which have been compared
with the existing species, and from Lower Tertiary beds in New Zealand
the late Baron Ettingshausen described some cones and twigs as _Sequoia
novae zeelandicae_ which bear a close resemblance to the existing
type. The available evidence would seem to point to a northern origin
of the genus, though allowance must be made for erroneous conclusions
based on negative evidence. Further research may well extend the past
distribution of Sequoia in southern lands, but the data to hand point
to the conclusion that the Californian trees represent the survivors
of a type which flourished in the Cretaceous and Tertiary periods over
a wide area in North America and in what we now call the Continent of
Europe.