252 APPLICATION OF PBINCIPLES. 



regulation of the quantity and quality of the earth, 

 the quantity of water, and the management of the 

 plants with respect to sun and shade, recourse is had 

 to a great variety of mechanical contrivances, to pro- 

 duce the desired shape. The containing flower-pot 

 is so narrow, that the roots pushing out towards the 

 sides are pretty effectually cramped. No radicle can 

 descend ; consequently it is only those which run to- 

 wards the sides or upwards that can serve to convey 

 nourishment properly, and it is easy to regulate those 

 by cutting, burning, &c., so as to cramp the growth 

 at pleasure. Every succeeding formation of leaves 

 becomes more and more stunted, — the buds and 

 radicles become diminished in the same proportion,— 

 till at length that balance between roots and leaves 

 is obtained which suits the character of the dwarf re- 

 quired. In some trees this is accomplished in two or 

 three years, but in others it requires at least twenty 

 years." {Hort. Trans., iv. 229.) 



We have still to consider that peculiar kind of pru- 

 ning which is technically called ringing {fig. 32.) 

 This consists in removing from a branch one or more 

 rings of bark, by which the return of sap from the 

 extremities is obstructed, and it is compelled to accu- 

 mulate above the ring. Mr. Knight explains the 

 physiological nature of the operation so well, that I 

 cannot do better than quote his words. 



" The true sap of trees is wholly generated in their 

 leaves, from which it descends through their bark to 

 the extremities of their roots, depositing in its course 

 the matter which is successively added to the tree ; 



