10 LINKS WITH THE PAST [ch. 



localisation of regions of cell-prodnction at the tips 

 of the elongating stem and root. These apical groups 

 of cells are, in fact, portions of the embryonic organism 

 Avhich persist so long as the plant lives. This con- 

 tinuity 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 genera- 

 tions suffice to carry our retrospect back to the days 

 when forests of oaks, birches, and other trees im- 

 peded 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 Avhich are as 

 sound as when first felled, recently discovered below 

 the foundations of parts of Winchester Cathedral con- 

 structed at the end of the twelfth or in the opening 

 years of the thirteenth century, are relics of Xorman 

 forests. In the course of some excavations at Brigg in 

 Lincolnshire in 188G 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 liaht induced the 



