In one of his essays Weismann quotes an old German saying with regard to comparative longevity, which asserts that 'a wren lives three years, a dog three times as long as a wren' and so on in a regularly ascending series: the life of a deer is estimated at three times that of a crow and an oak three times that of a deer, which means that, computed on this basis, an oak lives nearly 20,000 years(3)! This fanciful illustration of the relative longevity of an oak is the expression of a truth, namely the superiority of trees over animals in regard to the duration of life. As a seventeenth-century translator of Pliny's _Natural History_ writes, 'In old times trees were the very temples of the gods: and according to that antient manner, the plaine and simple peasants of the country, savouring still of antiquity, do at this day consecrate to one God or other, the goodliest and fairest trees that they can meet withal.' Oaks growing in Pliny's day in the Hercynian forest are said to have been there 'ever since the creation of the world(4).' Sir Joseph Hooker, in an account of some Palestine oaks, gives a drawing of a famous tree at Mamre, known as Abraham's Oak, which is supposed to mark the spot where the Patriarch pitched his tent(5). Examples such as these, though of no scientific value, serve to illustrate the well-founded belief in the extraordinary longevity of trees. In the absence of evidence to the contrary, it would be rash to deny the possibility that William the Conqueror's Oak in Windsor Forest, described by Loudon in his _Arboretum Britannicum_ and mentioned by later writers, may be a survival from the reign of the king whose name it bears. Although it is seldom possible to state with confidence the exact age of old oaks and yews famed for length of days, there can be no doubt as to the enormous antiquity of many of our trees whose years are 'sacred with many a mystery.' The section of a trunk of one of the mammoth trees of California (_Sequoia gigantea_) exhibited in the Natural History department of the British Museum, shows on its polished surface 1335 concentric rings denoting successive increments of wood produced by the activity of a cylinder of cells situated between the hard woody tissue and the bark. It is generally assumed that each year a tree produces a single ring, though, as is well known, an estimate of age calculated on this assumption cannot be regarded as more than an approximation to the truth. If this giant tree, which was felled in 1890, was then 1335 years old, it had already reached an age of over two centuries when Charlemagne was crowned Emperor at Rome. The concentric rings on a tree trunk owe their existence to certain structural differences between the wood formed in the spring and in the late summer. In Sequoia, as in other members of the great class of cone-bearing trees, the wood is composed of comparatively narrow elements which serve to carry water from the roots to the branches and leaves.