Institute of Paper ^Chemistrv (9), the Connecticut Agricultural Experiment 

 Station, and Yale School of Forestry (7). liesults of these incomplete 

 tests are summarized in Table 2, uo specific correlation betvveen silica 

 content and marine borer resistance has been attempted inasmuch as samples 

 for chemical analysis ytere not necessarily obtained from the same logs nor 

 even from the same country of origin as v/ere the exposure specimens. In 

 a number of instances, chemical analyses we:^e conducted upon composite 

 samples of savfdust representing a mixture obtained from several different 

 sources. 



Total ash content v/hich generally am.ounts to less than 0.5 per cent of , 

 oven-dry weight for domestic v/oods is seen to range as high as 2 per cent 

 in some of these woods. In those woods for which spectrographic data on 

 silicon in the ash are available, this element is seen to vary from v;eak 

 to very strong, in the latter instances amounting to one-half to two-thirds 

 of the total ash v:hen expressed as silica (SiOp) as shown in the chemical 

 analysis. It should be borne in mind that the spectrographic technique used 

 here permits only of an estimation of the proporbi.onate amount ox silica 

 in the total ash content. A strong indication of silicon in the ash of a 

 species such as Greenheart, which is extremely low in ash, ?rould therefore 

 not be as significant as a strong line in a wood like Teak virhich is high 

 in total mineral content. 



In the chemical analyses, silica is expressed as a percentage of oven-dry 

 weight, ranging from 0<,000 to l,5l per cent among these species. Unfortu- 

 nately these studies are not yet complete and only limited data are presently 

 available. However, yhen allowance is made for variability ;7ithin a species 

 from one source' to. another, 'the evidence appears to confirm the reputed 

 influence of silica content unon marine borer resistance. Of several species 

 that consistently sho-n a silica content of 0.20 per cent or more in these 

 analyses including Angelique, Teak, and Black Kaiceralli, only Teak was found 

 not to have a favorable de -ree of resistance to borers. .'ise (9) cites 

 the work of Bromley and Rudge to indicate the wide variation in mineral 

 content of Teak. On the basis of analyses of ten samples of this species, 

 variation in total ash was found to range from 0.6ii to Ii.3 per cent Virith 

 a silica range of 0.03 to 3.0 per cent. 



Looking at the negative side of this relationship, however, a nimiber of 

 the resistant species such as Acapd, Determa, and the vell-knovm Greenheart 

 are extremely low in silica and therefore must owe their resistance to 

 other factors. Variability may be involved her;, too, A specific example 

 is that of Acapu (Vouacapoua americana ) which was found by Edmondson to 

 be lacking in marine borer resistance~in Hawaii (1|), In the case of Green- 

 heart, 'ise has suv-ested that resistance to Teredo may be due to the 

 appreciable amounts of alkaloidal material present in the wood (9). 



It would appear to be reasonable to anticipate favorable marine borer resis- 

 tance for woods characterized by high silica content, even though resistance 

 is not exclusively dependent u-on silica content. High density of a wood 

 is not an appreciable deterrent to marine borer activity as evidenced by 



T - 9 



