[11] Hartig finds the specific gravity of the wood in a tree is increased from 0-60 to 0.74 when the surrounding wood has been cut down.--_Bot. Central_, vol. xxx, p. 220. If one realizes all these dangers from insects, animals, and storms, the height to which some trees grow and the age to which they live become matters for astonishment and surprise. The tallest trees in the world are probably certain Eucalyptus of Australia, which have obtained a height of 495 feet above the ground. They are by no means the _longest_ plants, for there are certain _rattans_ or canes, climbing plants belonging to the Palm family, which may be 900 feet long, although their diameter is not more than two inches.[12] There are also certain Seaweeds in the Southern Ocean, off the coast of Chile, which attain a prodigious length of 600 feet (_Macrocystis pyriferus_, or "Kelp"). That is not so remarkable, for their weight is supported by other plants in the case of the rattans, and as regards the seaweeds, by the water in which they float. [12] Bonnier, _Cours de Botanique_. The next in order to the Eucalyptus are those well-known Mammoth or Big trees of California (_Sequoia gigantea_). They grow only in certain valleys in the Sierra Nevada, at an altitude of 5000-8000 feet. Their height is usually given as from 250-400 feet, and the diameter sometimes exceeds thirty-five feet. Since they have become a centre of the tourist-industry in the United States, various methods have been adopted to make their size more easily realized. Thus a coach with four horses and covered by passengers is (or used to be) driven through a gateway made in one of them. The trunk of another has been cut off some feet from the ground, and a dancing-saloon has been made on the stump. It is at least doubtful if dancing would be very agreeable upon such a cross-grained sort of floor! A complete section of one of them was carried across the United States to make a dining-room table for an American millionaire. The age of one of these trees has been estimated at 3300 years. That is to say that it was a seedling in 1400 B.C., and has been peacefully growing in a Californian valley during all the time when Greece, Rome, Spain, France, Britain, and of course the United States, developed their civilizations. The specimen of the Mammoth tree in the Natural History Museum in London was 1335 years old.