!02 THE ART OF CULTURE. 



i;i the -roots, but in the woody substance of the stem. The 

 quantity of sugar in the sap augments until it reaches a certain 

 height in the stem of the plant, above which point it remains 

 stationary. 



Just as germinating barley produces a substance which, in 

 contact with starch, causes it to lose its insolubility and to become 

 sugar, so in the roots of the maple, at the commencement of vege- 

 tation, a substance must be formed, which, being dissolved in 

 water, permeates the wood of the trunk, and converts into sugar 

 the starch, or whatever it may be, which it finds deposited there. 

 It is certain, that when a hole is bored into the trunk of a maple- 

 tree, just above its roots, filled with sugar, and then closed again, 

 the sugar is dissolved by the ascending sap. It is further possi- 

 ble that this sugar may be disposed of in the same manner as 

 that formed in the trunk; at all events, it is certain that the' 

 introduction of it does not prevent the action of the juice upon 

 the starch ; and since the quantity of the sugar present is now 

 greater than can be exhausted by the leaves and buds, it is ex- 

 creted from the surface of the leaves or bark. Certain diseases 

 of trees, for example that called honey-dew, evidently depend on 

 the want of the due proportion between the quantity of the azo- 

 tized and that of the unazotized substances which are applied to 

 them as nutriment. 



If now we direct our attention to the particular organs of a 

 plant, we find every fibre and every particle of wood surrounded 

 by a juice containing an azotized matter ; while the starch, 

 granules, and sugar, are enclosed in cells formed of a substance 

 containing nitrogen. Indeed everywhere, in all the juices of the 

 fruits and blossoms, we find a substance destitute of nitrogen, 

 accompanied by one containing that element. 



The wood of the stem cannot be formed, qua wood, in the 

 leaves, but another substance must be produced which is capable 

 of being transformed into wood. This substance must be in a 

 state of solution, and accompanied by a compound containing 

 nitrogen ; it is very probable that the wood and the vegetable 

 gluten, the starch granules and the cells containing them, are 

 formed simultaneously, and in this case a certain fixed propor- 



