14 BULLETIN 1231, U. S. DEPARTMENT OF AGRICULTURE. 



inch thick. These experiments were begun on April 10, 1913. The 

 blocks were examined twice each year. Similar test blocks were sent 

 to the Tropics (Brazil, Ecuador, and Cuba) for test under more 

 severe conditions. 



In the experiments untreated woods and certain treated woods 

 failed after 6 months' exposure to the attacks of termites. This is 

 a very severe test for finished forest products, since in use they 

 would not be placed in the ground. 



After a three-year test, it was found that tropical woods, such as 

 teak, mahogany, and peroba, while resistant to termite attack, are 

 not wholly immune; they stand in the order named in comparative 

 immunity. 



The woods from the northeastern part of the United States, un- 

 treated, are very susceptible to attack. Treatment with paraffin 

 accomplished nothing, as the woods were readily attacked and also 

 suffered decay. Treated with chlorinated naphthalene, the woods 

 from the Northeastern States were attacked but little, comparing 

 favorably with untreated teak and mahogany. (Table 5.) 



Many preservative treatments for furniture and cabinet woods are 

 objectionable, since they discolor or will not permit fine finishes. 

 In these cases the hidden, interior parts may be so treated and then 

 be covered by veneers of cabinet woods which are resistant to attack 

 by termites. 



TERMITE-RESISTANT WOODS. 



The results of tests conducted from 1913 to 1922 at Falls Church, 

 Va., and inspections in the field by the writer, appear to warrant 

 the statement that there is no species of tree the wood of which is 

 absolutely immune to attack by termites. Nevertheless, the heart- 

 wood of certain trees is very resistant to attack by termites (Reticu- 

 litermes sp.). 



Among the most resistant woods which were tested are teak 

 (Tectona grandis) and sal (Shorea robusta) of India; cypress-pine 

 (CaUitris robusta) and camphor wood (Cinnamomum camphora) of 

 the Orient ; greenheart {Nectandra rodiaei) of South America ; red- 

 wood (Sequoia sempervirens) (PL II, figs. 3, 4) ; western red cedar 

 or giant arborvitae (Thuja plicata); 2 incense cedar (LObocedrus 

 decurrens) ; Port Orford cedar (Ghamaecyparis la/wsonicma) ; yel- 

 low cypress (Ghamaecyparis rvoothatensis) , and species of Junipers 

 (Juniperus spp.) of the United States. 



Certain other South American and Philippine woods were tested 

 on too small a scale to warrent definite statements as to their relative 

 resistance to attack by termites. Many of these woods may prove to 

 be very resistant. Further tests should be made. 



It is the presence of certain chemical constituents of the wood 

 which renders it resistant. Stakes of longleaf pine (Pinus palustris) 

 of Texas, cut from butt logs containing a large resin content (locally 

 called "f atwood " or " lightwood ") remained unattacked by termites 

 after being set in the ground exposed to their attacks from 1913 to 

 1922, whereas normal pine wood is very susceptible to attack by 

 termites. 



2 Bed cedar poles are seriously damaged by termites (Kalotermes) in California. 



