96 MISSOURI BOTANICAL GARDEN BULLETIN 
If the cavity is long it is advisable to cut the metal into two 
or three sections, one lapping the other about 2 inches. The 
metal is painted over on the outside. Sheet zinc, copper, 
galvanized iron, and sheet iron are all used for the purpose, 
tin being used least of all, the term “tinning” being generic. 
The best of the materials is zine, gauge No. 9. 
Where appearances do not count, when trees are badly 
damaged or have irregular cavities difficult to fill, the “open 
system” may be used. This consists simply of excavating 
and painting the entire cavity. This method is advan- 
tageous because it permits constant observation of the inside 
of the cavity, while fillings do not, it is quite cheap, less 
sound wood is cut, and it keeps out the fungi and insects 
quite as effectively as a filling. It has the disadvantage of 
not having any strength and of marring the beauty of the 
tree, but is finding many advocates. 
Bracing is one of the essentials in tree surgery, particu- 
larly in preventing of wounds and consequent decay. Limbs 
require bracing when they are likely to get wrenched from 
the trunk, when they are decayed, when the wood is brittle, 
and when a tree is forked. The old style of bracing con- 
sisted of placing an iron band around the limb and con- 
necting it with a chain to a similar band around the main 
trunk. The bands cut into the wood and killed the cam- 
bium, thus defeating the very purpose for which they were 
used. For best results an eye-bolt should be run through 
the limb and connected to another eye-bolt inserted in the 
trunk, by means of cable rope or iron rods. The cable is 
rather difficult to work, but after it is up, is the most satis- 
factory of any’ braces. In bracing small limbs several 
strands of galvanized wire should be run through the two 
eye-bolts, then bound together with a wire, and tightened by 
screwing on the nut of the eye-bolt. The eye-bolts will 
very from %g—%4 inches, depending upon the size of the 
limb. The braces should be placed as high as possible, for 
according to the physical law of lever and fulcrum the fur- 
ther from the crotch is the support the less strength is re- 
quired. Small trees may have their limbs braced by means 
of large screw eyes and fence wire, or the wire may be run 
through an opening in the limb double its diameter, and 
back again. A groove should be made at the back of the 
limb and a nail inserted under the wire to prevent it from 
slipping out. 
_ Many modifications of these methods are employed. For 
limbs overloaded with fruit a stick with an iron peg at the 
end is inserted into a hole on the under side of the limb. 
