130 THE ART OF CULTURE. 



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 vegetation, 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 ascend- 

 ing sap. It is further possible, that this sugar may 

 be disposed of in the same manner as that formed 

 in the trunks ; 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 sugar present is now greater than can be ex- 

 hausted by the leaves and buds, it is excreted from 

 the surface of the leaves or bark. Certain diseases 

 of trees, for example that called honey-dew, evi- 

 dently depend on the want of the due proportion 

 between the quantity of the azotised and that of 

 the unazotised substances which are supplied to 

 them as nutriment. 



In whatever form, therefore, we supply plants 

 with those substances which are the products of 

 their own action, in no instance do they appear to 



