No. 4.] 



TREE SURGERY. 



453 



AVhen we remove a limb, we cut across the grain of the 

 wood where the branch leaves the tree. Every portion 

 of the wood surface which is thus exposed dies. We know 

 how readily water enters the " sawed-off " end of a dead 

 log, and how wood rot follows. A similar process now takes 

 place in the wound ; a dark 

 stain first penetrates the wood, 

 steadily spreading inward 

 from the surface. This works 

 down toward the heart of the 

 tree, and is followed by wound 

 rot. If a living green branch 

 has been removed, the surface 

 of the wound dies and cracks, 

 leaving open channels for the 

 entrance of water and the 

 spores of parasitic fungi. If 

 the branch cut off be already ^ ,- t> ■ * ^ • ' f. 



•^ Fig. 17. — Beginuing of decay in centre 

 dead, decay may have been of wound (allowed by delaying amputa- 

 , 1 . ,1 . tion too long). 



communicated to the tree 



trunk. Such decay begins or is preceded by a discoloration 

 in the first annual ring, close to the heart or " pith" of the 

 branch. This discoloration may extend many feet down and 

 into the trunk, so that when the Imib is removed the wound 

 may present an appearance like Fig. 17. 



Now, if in either case the wound is very small, it may 

 heal soon enough to prevent serious decay of the trunk, but 

 a large wound certainly will not. The only safe treatment 

 is to cover all wounds on deciduous trees, and the larger 

 ones on coniferous trees, with some fluid substance which in 

 drvino; and hardenino^ will close the ends of the channels 

 in the wood, and prevent decay until the tree can cover 



which push their way through the i^its into the cavity, and may there divide 

 and grow further), which both prevent the entrance of rain water and the 

 evaporation of any water that may be present in these organs. In the second 

 place, gums are formed in abundance in the neighborhood of the wounded 

 surface, and these fill up and close the lumiua of the organs, especially the 

 vessels, thereby protecting them, to a certain extent, against prejudicial influ- 

 ences of the environment. . . . The foregoing protective agencies are, however, 

 insuflScient to afford absolute security to the exposed wood against decomposi- 

 tion and decay." (" Diseases of trees," by Prof. R. Hartig.) 



