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.
Fig. 16. A. Agathis robusta Muell. (much reduced). B. Agathis Moorei Lind. (1/2 nat. size).]
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.