168 



the wood exposed on the surface of the wound, it is important 

 to see that rain water is not allowed to lodge on the wound 

 and that air is excluded as far as possible. In Conifers the 

 wound is often well protected by a copious exudation of resin 

 and in many Dicotyledons gums, to a certain extent, serve 

 the same purpose, but it is always best to cover the cut 

 surface with wood tar, or some other substance, which will 

 not interfere with the process of occlusion and will prevent air, 

 water, and fungus spores obtaining access to the wound until 

 the healing is complete. In connection with artificial pruning 

 may be mentioned the case of the lower branches of trees 

 growing in a dense wood, which are killed by the heavy shade. 

 If such branches are .small their wood is usually soft, which 

 soon becomes quite rotten. Such branches in consequence 

 quickly fall or are broken off close to the stem and, the 

 wound soon healing, little harm is done. In the case of larger 

 branches, however, which often contain well marked heart-wood, 

 the dead stumps persist for several years and, as the stem in- 

 creases in thickness, these gradually become enclosed in the 

 wood of the stem. No intimate union being possible between 

 the dead stumps and the living tissues of the stem which 

 gradually envelop them, such stumps form knots in the wood 

 which may fall out after conversion and cause holes. In 

 addition to being a source of weakness such stumps are usually 

 more or less decayed and may cause wide-spreading decay in 

 the sound wood of the stem. 



Girdling or 147. Killing trees by girdling or 



Ringing. ringing is a common forest operation, e.g. in the case 

 of Teak in Burma. If a deep circular cut is made in a 

 Teak tree, down to, and into, the heart-wood, thus com- 

 pletely severing the connection between the layers of 

 cortical tissue and sap-wood situated respectively above 

 and below the wound, the tree will quickly die. This is due 

 to the fact that the heart-wood is incapable of water conduc- 

 tion, and hence the transpiring crown of the tree situated 

 above the girdle no longer receives, from the soil, the ne- 

 cessary supplies of water to replace that lost by transpiration 

 and the ultimate death and drying up of all parts above the 

 ring is consequently assured. This, generally speaking, holds 

 good for all trees which possess a well-marked heart-wood. 

 Trees, however, which possess no distinct heart-wood can also be 

 killed by girdling, e.g. the Himalayan Spruce and Silver Fir, but 

 in the case of such trees the effect of girdling is frequently very 

 slow, the trees often remaining alive for several years. In such 



