increase the supporting power of the tree and enable it to sustain the added burden of the annual increase in the weight and extent of its spreading branches. It is the persistence of permanently juvenile tissue in certain regions of a tree, together with the remarkable power of repairing injuries and shedding effete parts, that constitute some of the most striking contrasts between the higher animals and plants. The embryo oak in the earlier stages of development consists entirely of actively growing cells; by degrees differentiation of the embryonic tissues results in the localisation of regions of cell-production at the tips of the elongating stem and root. These apical groups of cells are, in fact, portions of the embryonic organism which persist so long as the plant lives. This continuity between the growing tip of an old oak stem and the cells of the undifferentiated embryo affords one of the most remarkable examples in nature of a link between the past and the present. If we pass beyond the stretch of time represented by the life of a single tree, a few successive generations suffice to carry our retrospect back to the days when forests of oaks, birches, and other trees impeded the progress of the Roman invaders, and, a stage farther back, to the age of Neolithic man whose remains are occasionally found in our heaths and moors and in the submerged forests round our coast. The blocks of oak and beech, some of which are as sound as when first felled, recently discovered below the foundations of parts of Winchester Cathedral constructed at the end of the twelfth or in the opening years of the thirteenth century, are relics of Norman forests. In the course of some excavations at Brigg in Lincolnshire in 1886 a dug-out boat was found nearly 50 feet long and from 4 to 5 feet in breadth. The stem of the oak from which the canoe had been fashioned shows no sign of branching for a length of over 40 feet, a fact which points to the growth of the tree in a forest where the race for light induced the development of clean columnar stems. The Brigg 'dug-out,' now in the Hull Museum, was discovered in an old alluvial valley of the Ancholme river, formerly connected with the Humber, and it may be that it was used by Neolithic man as a ferry for river-service(7).