WOUNDS 259 



partly to the consequent negative pressure of the air in the 

 tree. 



When pruning is undertaken in spring or summer, the tar 

 altogether fails to enter the wood, and the thin superficial layer 

 does not prevent the cut surface from drying later, and forming 

 fissures into which water and fungi may gain an entrance. And 

 then, again, the separation of the crushed cortex from the 

 lower edge of the wound frustrates the object of tarring. 



From what has been said, it follows that dicotyledonous trees 

 may be best pruned in the months of October, November, and 

 December perhaps also in January and February and that a 

 good coat of coal-tar should at once be applied to the wounds. 



Hitherto pruning has usually been undertaken in summer, and 

 this explains why the operation has caused such enormous 

 damage to trees, especially the oak. It is, however, desirable 

 from every point of view that the subject be further investi- 

 gated with scientific accuracy. Several species of trees should 

 be taken in hand, because the trials which I conducted were 

 confined to the oak, and even in their case sufficient time has 

 not yet elapsed to make it possible to furnish conclusive 

 answers to all the questions that have just been raised. 1 



SHORTENING OF BRANCHES 



The shortening of the branches of plants from three to ten 

 or twelve feet in height differs from pruning proper only as 

 regards the size of the branches. Most of what has been said 

 in connection with pruning may be applied here. It therefore 

 follows that all shortening of branches is an evil which can only 

 be excused when important objects are to be gained. The 

 dressing of the younger classes of plants is most admissible at 

 the time of transplanting, when the number of the roots has been 

 considerably reduced. In the early part of the season when 

 foliage is scarce, and when^ transpiration of water proceeds but 

 slowly, the quantity of roots may suffice ; whereas in summer 

 the diminished mass of roots may be unable to provide sufficient 



1 It is very desirable that observations be continued on some 240 pruning 

 experiments that I carried out in 1875 in the woods attached to the Forest 

 School of Eberswalde. 



S 2 



