36 CLIMATIC CYCLES AND TREE-GROWTH 



borers for greater depth in the tree will probably have to be made in 

 single pieces of tubing. 



The tubular borer — This borer was designed especially for the 

 dried and sometimes very hard logs in the prehistoric ruins. It will 

 work on pine trees and junipers. It gives a core 1 inch in diameter, 

 which means a better chance of finding obscure rings than in the 

 increment-borer cores. The borer is a 1-inch steel tube with small 

 sawteeth at one end and a projection at the other for insertion in a 

 common brace. Collections to date include some 30 or 40 very valuable 

 cores made with this instrument. In actual operation the core has 

 been broken off and drawn out about every 3 inches in order to help 

 get rid of sawdust. This extraction is done by a i-inch steel rod 

 with a wedge at one end for breaking the core off and a screw at the 

 other end to catch the core fragment and draw it out. 



There are two chief problems with a borer of this sort — sawdust 

 and the labor in pressing the borer into the tree or log. For the former 

 a 1-inch auger hole carried below the borer hole and a little in 

 advance has been used advantageously, but frequent breaking of the 

 core is more certain. For the latter a chain-drill attachment was tried 

 unsuccessfully, as it cracked the borer. An auger guide for limited 

 depths is working extremely well in some cases. This guide is a hollow 

 cylinder 4 inches long and 2 inches diameter, with thick walls. Length- 

 wise down these walls i-inch holes are placed fairly close to each 

 other. This guide is screwed to the tree or log with the guide-holes 

 pointing toward the center of the tree. Then a small auger bores into 

 the tree through the holes in succession. The guide is then removed 

 and the tubular borer quickly frees the core. In this arrangement 

 the auger holes take care of the sawdust and the auger itself needs no 

 pressure for forcing it into the wood. The core is not so presentable 

 in appearance, but is easily rounded to a desirable form. This makes 

 a very good form for use on prehistoric beams, but does not solve the 

 problem of deep boring in living trees. A device using the principle 

 of the chain-drill attachment is now under test. There is no doubt 

 that a suitable depth borer can be developed. An effective length of 

 28 or 30 inches would be enough for the yellow pines. A borer to go 

 12 feet into big sequoias would probably have to be designed for use 

 with an engine or motor. One would have to be sure beforehand that 

 living trees would supply data worth the trouble. 



Injury to living trees — It has been an invariable custom to plug 

 the holes made in living trees so as to keep out any possible infection. 

 This is easily done with a small branch from the same tree, cutting 

 the bark entirely away, so that only healthy sapwood goes into the 

 hole. This amounts to grafting a young branch onto the trunk. Even 

 without this precaution it is not probable that any harm results, as the 

 holes quickly fill with sap or pitch. 



