DISCOLOURATION. 



143 



that the sapwood immediately inside the cambium is not 

 killed by the frost, but its vitality is so impaired that it 

 cannot form thyloses, nor is its contained starch converted 

 fully into tannin, as in ordinary oak heartwood. Such wood 

 is therefore internal sapwood, differentiated from normal 

 heartwood by its light colour and by the presence in it of 

 starch ; its vessels also are without thyloses, so that it absorbs 

 antiseptics which normal oak heartwood will not absorb. 

 Hence if a solution of sulphate of copper be poured on the 

 transverse section of the wood and the wood dried, the 

 internal sapwood has a bluish tint, while the normal heart- 

 wood retains its natural colour. Henry, Professor of Natural 

 History at Nancy, showed 

 that both external and inter- 

 nal sapwood contains only 

 up to 2 per cent, of tannin, 

 while heartwood contains 

 6 to 7 per cent., the quantity 

 diminishing as true sapwood 

 is approached. 



Mer examined numerous 

 specimens of oakwood at 

 Nancy and found that the 

 most recent ring- shake in 

 them dated from 1879, a 

 severe frost-year, after which 

 for several years narrow annual zones of normal heartwood 

 were produced, followed by zones of heartwood of ordinary 

 width. The zones for several years anterior to 1879 were of 

 ordinary width, but were not converted into heartwood, and 

 formed the belt of internal sapwood. Mer found many cases 

 of internal sapwood dating from frost-years earlier than 1879, 

 such as the severe winters of 1829, 1794 and 1789 ; those of 

 1879 were quite sound, but those of 1829 were red, showing a 

 commencement of decay, and those of 1794 and 1789 were 

 brow r n and decayed, emitting a fetid odour not found in wood 

 suffering from red-rot and said by Mathey to be caused by a 

 decomposing ferment produced by Amylobacter. Fig. 60 shows 

 internal sapwood, (a) sound and (b) unsound, though it is not 



Fi;_r. (it), hitcniiil 

 a Pale, h K.-.I. (After Boppe.) 



