20 THE BUILDING UP OF THE 



ceeding from the bud at the summit of the vegetable cone, 

 continue the growth of the main axis or stem, whilst those 

 developed from the lateral buds give birth to branches. If 

 now these new growths be carefully examined, it will be 

 found that the new generation of leaves has constructed 

 them on precisely the same plan as the first year's shoot. 

 For these branches, and the addition which has been made to 

 the stem in height, consist of precisely the same parts, viz. : 

 a conical axis and leaves with buds in their axilla, and a 

 terminal bud at the apex. Each new axis or shoot which 

 has been superadded to the first year's shoot, must there* 

 fore be regarded as a simple repetition of the first year's 

 shoot. 



It is also plain that the branches are to the main axis or 

 stem, the second year, what the leaves were to it the first 

 year, performing precisely the same functions, only in a far 

 more energetic manner; because in this case it is not one but 

 several leaves which are engaged in elaborating the sap, 

 which, when duly prepared in the leaves, passes from them 

 into the main axis or stem of the tree through the common 

 axis of the shoot, and thus contributes to its nutrition. 



The tree has therefore a much greater amount of leaf-sur- 

 face at work in the air the second year than it had the first, 

 and its chances of life are consequently multiplied a 

 thousand fold. For with every addition to the number of 

 its leaves, the tree obtains a new instrument for extracting 

 nutriment from the atmosphere, and elaborating such food 

 as it attracts to itself from the soil. The amount of wood 

 and bark formed is therefore much greater the second year 

 than the first; it is, in fact, exactly proportionate to the in- 

 crease in the extent of leaf-surface and the vital activity of 

 the leaves themselves. 



The sap having been exposed to the air and light in these 

 additional leaf-surfaces, is again rendered nutritious, and 

 not only contributes to the elongation of the stem and 

 branches, but at the same time to the formation of a new 

 conical layer, or enveloping mantle of wood and bark, be- 

 tween the wood and bark of the previous year. Each shoot, 



