26 



VITAL ACTIONS. 



over the wood {fig. 2. b), and form a coating, below 

 which new liber and alburnum may be generated. 

 In cuttings, the " callus," 2 



which forms at the end pla- 

 ced in the ground, is the 

 cellular horizontal system, 

 preparing for the reception 

 of the perpendicular sys- 

 tem, which is to pass down- 

 wards in the form of roots. 

 Many plants will endure 

 extensive lacerations of 

 their surface, and close up 

 such .wounds with great 

 facility. The well known 

 fact of large inscriptions 

 cut in trees below the bark 

 (which inscriptions were 

 effected by removing very 

 broad spaces of the bark and wood) being covered 

 over in time by new bark and wood, so as to be 

 no longer visible from the outside, sufficiently proves 

 this. In such cases, however, the reparation of the 

 injury takes place chiefly, if not exclusively, by the 

 annual addition of new matter to the lips only of the 

 wound, the effect of which is to reduce the circle 

 annually to a less diameter, till at last the centre is 

 closed up. 



48. In the bark of trees and shrubs two distinct 

 parts are found : the one external and cellular ; and 

 the other internal, resting upon the wood, and con- 



