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.
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 31/2 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.