24: L£!SSOJ\S WITS PLANTS 



represent sections of dead or live branches ; and each 

 one records an event in the history of the tree. 



23. A limb was sawn from a tree. Several years 

 afterwards a drawing was made of the stub (Fig. 

 21). The limb had not yet healed in. The reason 

 is apparent: the stub had been left so long that 

 the tissue had not yet been able to pile up over 

 it, and, having no life in itself, the branch could 

 not make healing tissue of its own. The stub is 

 now a monument to the man who pruned the tree. 

 Fig. 22 shows how another limb was cut, and 

 although the wound is not nearly so old as the 

 other, it is being rapidly closed in. There are most 

 important practical lessons, then, to be learned from 

 the study of knot-holes, — two of which are that 

 nature is a most heroic pruner, and that limbs must 

 be sawn off close to the parent branch if the 

 wounds are to heal well. 



Suggestions. — The pupil should determine whether cross-sections 

 of large branches (as in Figs. 21 and 22) really ever heal up (as 

 wounds heal in human flesh), or whether they are simply her- 

 metically sealed by a covering of tissue which arises from the 

 sides of the wounds. In other words, does the end of the stub or 

 wound ever become vitally connected with the healing tissue, or 

 does this old wood remain lifeless and inert under the healing tissue 

 as some foreign body (as a nail) might ? Let the pupil procure a 

 healed -over wound and split it lengthwise, and then answer these 

 questions. The student should also observe the healing of wounds 

 upon street trees and in orchards as related to the length at which 

 the stub is left. Examine the knots in the floor and the wood-work. 



