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 (eticw- 
litermes sp.). 
Among the most resistant woods which were tested are teak 
(Tectona grandis) and sal (Shorea robusta) of India; cypress-pine 
(Callitris robusta) and camphor wood (Cinnamomum camphora) of 
the Orient; greenheart (Vectandra rodiaei) of South America; red- 
wood (Sequoia sempervirens) (Pl. I, figs. 3, 4); western red cedar 
or giant arborvitae (Thuja plicata);* incense cedar (Livocedrus 
decurrens); Port Orford cedar (Chamaecyparis lawsoniana) ; yel- 
low cypress (Chamaecyparis nootkatensis), 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 “fatwood ” 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 Red cedar poles are seriously damaged by termites (Kalotermes) in California. 
a. = |. 
