TREE-FORM OUT OP ITS UNIT. 21 



with its system of leaves, contributes its part to the newly- 

 formed layer, and the growth of the stem, in length and 

 thickness, thus takes place at the same time. 



Toward the close of the growing season, the sap is again 

 diverted from the leaves to the buds forming in their axilla; 

 and the protective leaves of winter having been fully ma- 

 tured, the second generation of nutritive leaves wither and 

 fall from the stem and branches as before. Our tree, when 

 defoliated, now shows a number of shoots associated together, 

 and developing from a common axis or stem, all of which 

 have been built up by leaves constructed on precisely the 

 same pattern as the first year's shoot, and prepared for 

 winter in exactly the same manner. 



The Third Year the tree presents the same general vegeta- 

 tive appearances. The terminal bud continues the growth 

 of the stem or main axis as before, the buds on the branches 

 develope into branchlets, and contribute to the further ex- 

 tension of the branches and to the growth of the shoots 

 forming at their summit; and the whole system of shoots 

 thus put forth, with their leaves, co-operate in the formation 

 of the sap into another enveloping mantle of bark and 

 wood, which covers the stem and branches of the previous 

 year. 



In precisely the same manner does the tree continue to 

 vegetate, every year increasing in size and strength, adding 

 to the number of its leafy operatives, and the amount of 

 labor done, until it attains its greatest elevation. 



A peculiar alteration in its habit now becomes noticeable. 

 For the sap is no longer expended in the extension of its stem 

 and branches, but in the formation of its flowers and fruit 

 The period of puberty has arrived, the tree is in the full 

 prime and vigor of life, and the growth of its stem and 

 branches is gradually retarded, the vegetative efforts of 

 each season being absorbed by the reproductive. The tree, 

 therefore, now preserves pretty much the same landscape 

 character and appearance year after year. 



Our readers will now understand that the laborers en- 

 gaged in building up the tree are its leaves; that these 



