GRAFTED TREES. 177 



produce a tree with plum roots and almond leaves. The 

 wood, however, of the stem will consist of four distinct 

 varieties, though formed from one continuous cambium la}'er. 

 Below the almond wood and bark we shall have perfect peach 

 wood and bark, then perfect apricot wood and bark, and at 

 the bottom perfect plum wood and bark. In this curious 

 instance we see the intimate correspondence between the 

 bark and the leaf, for if we should remove the • almond 

 branches we might cause the several sorts of wood to develop 

 buds and leafj twigs each of its own kind. Each section of 

 the compound stem has its seat of life in the cambium, and 

 the cambium of each reproduces cells of its own species out 

 of a common nutrient fluid. 



Thus there is seen to be a flow of crude sap upward in the 

 wood, and a flow of organizable material essential to the life 

 of the plant, proceeding from the leaf to the root through 

 the bark and cambium layer. From this perfected sap the 

 growth of the season is formed, and provision for the begin- 

 ning of the next season's growth is also stored up, commonly 

 in the root. As the fact of a rootward flow of elaborated sap 

 is very generally denied at the present time, it may be well 

 to quote a single line from the edition, published in 1870, of 

 the admirable text-book on botany by the late Professor 

 Henfrey, of London, which has been carefully revised by 

 Dr. Masters. In reference to this subject he says, "The 

 evidence of a descent of elaborated sap is overwhelming." 

 There is then a peculiar motion or circulation of the fluid 

 contents of every living cell, called cyclosis or rotation 

 of sap, and there is a general movement of fluids upward 

 and downward in the entire plant, which may be named cir- 

 culation of sap. The upward flow is vastly greater and more 

 rapid than the downward, but the motive power in all three 

 of the cases specified is unknown, except we rest satisfied 

 with the old-fashioned and, to some persons, unphilosophi- 

 cal, but nevertheless real and most wonderful power called 

 vital force, which in the living vegetable cell subordinates 

 all other forces. 



Numerous hypotheses have been advanced to account for 

 the circulation of sap through the operation of some merely 



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