IX] ANNUAL GROWTH 71 



consequent on the replacement of the epidermis by cork, 

 the completion of its first year's wood, and other events 

 comprised in the gardener's phrase "ripening of the 

 wood," it is for many reasons useful to call the altered 

 shoot a twig ; later on the twig will become a branch, or, 

 when large and of timber size, a limb. 



The actual length attained in the annual growth by a 

 shoot varies from a few millimetres to more than a metre, 

 according to the species, the environment good or bad 

 soil, exposure to light, amount of water, temperature, &c. 

 and the age of the tree or shrub. 



This is well shown by the leader, as the terminal shoot 

 of the stem is called, of several of our trees. The rule is 

 that the leader grows rapidly in its earlier years, and 

 more and more slowly i.e. adds a diminishing increment 

 of length annually as the tree reaches its maximum 

 height. Measurements have shown that the leading shoot 

 of the Larch during its second year may extend a foot or 

 more, and in its third year one and a half feet, and so on 

 for several years, rapidly growing up to its maximum 

 height ; while the leader of the Silver Fir will grow only 

 one to three centimetres in the same period, and must be 

 regarded as a slow grower. 



The leader of a Spruce in my garden, in February, 1904, 

 when the tree was twelve years old, was just over 70 cm. 

 long i.e. it had elongated to that extent during the 

 past wet summer; while that of an Oak of about the 

 same age had not extended more than 20 cm. or so, 

 and that of a Beech less than 12 cm. during the same 

 season. 



It is stated that the rapidity of growth during early 

 youth is related to the capacity of the tree to endure 

 shade, and that the extensive growth of the Birch, Alder, 

 Aspen, Ash and Scots Pine all plants which endure shade 



