October 12, 191 i] 



NATURE 



505 



Hon of trees of a bygone age is supplied by the volcanic 

 strata of Lower Tertiary age exposed on the slopes of 

 Amethyst Mountain, in the Yellowstone Park district. At 

 different levels in the 2000 feet of strata as many as fifteen 

 ts are represented by erect and prostrate trunks of 

 p> trified trees. The microscopical examination of some of 

 trees shows that they bear a close resemblance to 

 S. sempervirens. In a photograph given to me by Dr. 

 Knowlton, of Washington, one sees living conifers of other 

 genera side by side with the lichen-covered and weathered 

 trunks of the fossil Sequoia, contiguous but separated in 

 time by millions of years. From Cretaceous rocks of 

 South Nevada, not very far from the present home of 

 Sequoia, petrified wood has been described possessing the 

 anatomical characters of the mammoth tree. While there 

 is little doubt that Sequoia formerly had its maximum 

 distribution in the northern hemisphere, there is some 

 evidence, though not conclusive, that the genus once 

 existed in Madagascar and in New Zealand. 



The Araucaria Family. 



Another and even more venerable section of the conifers 

 is represented by the Araucaria family, which includes 

 two genera, Araucaria and Agathis. The best known 

 species of Agathis, or Dammara as it is sometimes called, 

 is the Kauri pine, probably the finest forest tree in New 

 Zealand. The stems reach a height of 160 feet, termin- 

 ating in tiers of spreading branches bearing thick and 

 narrow leaves 2 to 3 inches long. The almost spherical 

 cones consist of a central axis bearing overlapping, broadly 

 triangular scales, each of which carries a single winged 

 seed. Other species of Agathis occur in the Malay Archi- 

 pelago, the Philippines, Queensland, and elsewhere. The 

 genus Araucaria, with the exception of the familiar 

 Monkey Puzzle (Araucaria imbricala) and a Brazilian 

 species, is confined within the geographical area occupied 

 by Agathis. In addition to the Monkey Puzzle, intro- 

 duced into England in 1796 from Chile, the Norfolk Island 

 pine {A. excelsa) is a commonly cultivated pot-plant in 

 this country ; it was introduced to Kew in 1793 by Sir 

 Joseph Banks soon after its discovery by Captain Cook. 



Before we consider the past history of the Araucaria 

 family, a word must be added in regard to the characters 

 which enable us to recognise Araucaria and Agathis in a 

 fossil state. The wood of these two genera differs in 

 certain minute structural features from that of other 

 conifers ; the examination of a radial longitudinal section 

 of a branch of one of the Araucarias under a microscope 

 shows on the walls of the elongated tubular elements of 

 which the wood consists small polygonal areas technically 

 known as bordered pits ; these occur in one or more rows, 

 and may be described as circles converted into polygons 

 by mutual pressure. In pines and other conifers these 

 bordered pits are circular or oval in form, and not, as a 

 rule, contiguous. The foliage shoots of Araucaria, though 

 fairly distinctive in the form and arrangement of the 

 leaves, may be confused with branches of other genera, 

 and are in themselves of secondary importance for diag- 

 nostic purposes. On the other hand, the seed-bearing j 

 scales of the large cones afford much more trustworthy 

 means of identification ; each scale bears a single seed 

 either immersed in the scale or lying in the middle of its 

 upper face. In other conifers two or more seeds occur on | 

 each scale. It is not possible as yet to give a definite, 

 answer to the question : How far into the past can we trace 1 

 the direct ancestors of existing species of Araucaria and 

 Agathis ? 



From Permian and Upper Carboniferous rocks foliage i 

 shoots have been obtained almost identical in form with 

 those of the Norfolk Island pine, and there is other 

 evidence of a more satisfactory kind pointing to the prob- 

 able existence in Palaeozoic floras of trees closely akin to 

 Araucaria. Araucarian types are recorded from Triassic 

 strain, but from rocks of Jurassic age Araucarian cones 

 and seed-bearing seeds, together with wood and foliage 

 shoots, have been found in greater abundance. Petrified 

 wood practically identical with that of the living species 

 is recorded from Lower Jurassic rocks at Whitby, and 

 there is reason to believe that some of the Whitby jet 

 owes its origin to Araucarian wood. 



A good example of a cone agreeing closely in structure. 

 as in size, with the cones of some species of Araucaria 

 NO. 2189, VOL. 87] 



was described in 1S66 by Mr. Carruthers from Jurassic 

 rocks at Bruton, in Somersetshire. Cone-scales exhibiting 

 the characteristic features of Araucaria have been found in 



1 the Middle Jurassic rocks of Yorkshire, in Jurassic rocks 

 of north-east Scotland, Cape Colony, Australia, India, and 

 in the eastern States of North America. In a collection 

 of Jurassic plants obtained a few years ago by members 

 of a Swedish Antarctic expedition in Graham's Land, Dr. 

 Nathorst has recognised some seed-scales of the Araucarian 



I type. As we ascend the geological series and pass into 

 Cretaceous strata, evidence of the wide distribution of the 

 Araucarieae is still abundant. Araucarian wood has been 

 discovered in Cretaceous rocks in Egypt, East Africa, 

 Dakota, and elsewhere ; and from beds of this age in New 

 Jersey Prof. Jeffrey and Dr. Hollich have recently described 

 several different types of fossils represented by petrified 

 leafy shoots and cone-seeds, some of which are closely 

 allied to Araucaria, while others are nearer to Agathis. 



In Tertiary floras undoubted Araucarian species are less 

 common ; it is not improbable that some foliage shoots 

 from the plant-beds of Bournemouth, described by Mr. 

 Starkie Gardner as Araucaria, may belong to a species 

 nearly related to the Norfolk Island pine. From the 

 extreme south of South America Araucarian wood and 

 branches have recently been recorded, and, at the other 

 end of the world, Tertiary rocks on the west coast of 

 Greenland have yielded fragments which, with some 

 hesitation, may be classed as Araucarian. 



One conclusion, which seems almost unavoidable, is 

 that the species of Araucaria and Agathis which survive 

 in South America and in the islands of the Pacific have 

 in the course of successive ages wandered from the other 

 end of the world. We can only speculate as to the causes 

 which have contributed to the changes in the fortunes of 

 the family ; but one thing is certain, namely,- that few 

 existing plants are better entitled to veneration as survivors 

 from the past than are the Monkey Puzzle and other 

 species of Araucaria. 



The Maiden-hair Tree. 

 In recent years the maiden-hair tree of China and Japan, 

 introduced into Europe early in the eighteenth century, has 

 become fairly well known in English gardens. There is 

 probably no other existing tree with so strong a claim to 

 be styled a " living fossil," to use one of Darwin's terms. 

 In 1712 the traveller Kaempfer proposed for this plant 

 the generic name Ginkgo, and Linnaeus adopted this 

 designation, adding the specific name biloba to denote the 

 characteristic bisection of the wedge-shaped lamina of the 

 leaf into two divergent segments. In 1777 the English 

 botanist Sir J. E. Smith expressed his disapproval of what 

 he called the uncouth name Ginkgo by substituting the 

 title Salisburia adiantifolia ; but the correct botanical name 

 is Ginkgo biloba. In its pyramidal habit Ginkgo agrees 

 generally with the larch and other conifers ; its leaves, 

 which are shed every year, are similar in form and vena- 

 tion to the large leaflets of some maiden-hair ferns. The 

 seeds, borne on fairly long stalks, are enclosed in a thick 

 green flesh, and in appearance resemble small plums. 

 For many years Ginkgo has been recognised by botanists 

 as an isolated and probably ancient type. It used to be 

 placed near the yew among the conifers ; but in 1896 a 

 Japanese botanist, Hirase, made the important discovery 

 that the male reproductive cells of the maiden-hair tree are 

 characterised by the possession of innumerable cilia which 

 enable them to swim in fluid like the male cells of ferns 

 and many other plants. In the true conifers the male 

 cells have entirely lost the power of independent move- 

 ment. Without going into details, the important point is 

 that Hirase's discovery confirmed suspicions based on 

 other characters, that Ginkgo was not a true member of 

 the conifers, and supplied a cogent reason for promoting 

 ft to a class of its own, the Ginkgoales. 



Though some travellers in China have spoken of Ginkgo 

 trees in a wild state, the balance of opinion is in favour 

 of regarding the genus as represented at the present day 

 solely by cultivated specimens. China was, no doubt, its 

 last stronghold ; in that country, as in Japan, it is re- 

 garded as a sacred tree, and planted in the groves of 

 temples, and it would seem that the fact of its being held 

 in veneration by the priests has saved it from extinction. 



As in many other cases, so in regard to Ginkgo we 



