PREVENTIVE AND COMBATIVE MEASURES. 77" 



■wound must remain open till completion of occlusion.'' If we followed 

 this view, then numerous wounds would be left freely open as entrances, 

 for wound-parasites, and serious loss would result. It is just the numerous 

 smaller wounds (e.g. those produced by hail), which are the principal places 

 of infection for species of Nectria, Cucurhitaria, Hymenomycetes, etc., in 

 fact, they form very convenient places whence a tree may be easily infected 

 artificially. 



The following points in regard to treatment of branches may 

 be conveniently summarized here. Trees in closed plantations 

 are naturally stripped of their branches by these dying in con- 

 sequence of deficient illumination ; they then break off, and 

 the short stumps are soon occluded or grown over. During 

 this process there is always a risk of infection by fungi, and 

 " snag-pruning " ^ is employed to shorten the period of occlusion 

 as much as possible. This at the same time prevents the in- 

 clusion of long branch-stumps in the timber, and reduces the 

 number of knots in sawn boards. Such dead snags or stumps 

 are deficient in nutritive materials and very dry, so that they 

 are less suited for the entrance of wound-fungi than wounds on 

 the living branch. 



The usual process of forest-pruning is necessary to produce 

 clean boles, to increase the illumination for undergrowth, or 

 to utilize the branches so removed. In the operation, all 

 branches should be cut off close to the shaft, no snags should 

 be left, nor must injury be inflicted on neighbouring bark. 

 The operation is best carried out in autumn or winter when 

 the bark is most adherent to the wood, occlusion then begins 

 with the renewal of vegetative activity in spring and is well 

 advanced by the time the greatest dispersal of fungus-spores takes 

 place. Infection by fungi will, however, be rendered quite 

 impossible if wounds are immediately painted over with tar, or, 

 in the case of smaller wounds on garden stock, with tree-wax ;. 

 these reagents, if applied in winter, will easily penetrate into the 

 wood, and even replace the formation of protective wound-wood. 

 Hartig says on this subject : ^ " tarring produces satisfactory 

 results only when pruning has been done in late autumn or 

 in winter, because it is only then that the tar is absorbed by 

 the surface of the wound. It would appear that the absorption 

 of tar is due partly to the diminished amount of water in the 



1 Trockenastung. ^ Hartig, Diseases of Trees. English Edit. p. 258-59. 



