338 E. M. Kindle — Fossilization of Palceozoic Tree-trunks. 



diameter. None of the trunks observed in the whetstone quarries, 

 whether large or small, showed any trace of woody tissue within the 

 bark, which was usually altered to coal. Similar sand-filled trunks 

 of Lepidode7idron and Sigillaria have been described by Dawson from 

 Joggins, Nova Scotia, and by various geologists from other localities. 

 The exact conditions under which the substitution of sand for woody 

 tissue within the bark occurred during the fossilization of the latter 

 have, so far as the writer is aware, never been illustrated by examples 

 from our present forests. Rational explanations of the obscure 

 phenomena of the past are often facilitated by means of the analogy 

 supplied by existing agencies. I may therefore venture to call 

 attention to the remarkable resistance to decay of the bark of the 

 common canoe-birch and the equally striking susceptibility to decay 

 of the wood of this tree. Consideration of the differential rate of 

 decay of the bark and the wood of the birch throws much light on 

 the process which has so often produced the kind of fossilization 

 represented by the sand-filled bark of the Lepidodendron. 



The decay of wood is essentially a biological process resulting 

 directly from the metabolism of the fungi and bacteria which gain 

 access to it. But since moisture and free oxygen are essential to the 

 life of these organisms, wood kept either in a very dry atmosphere or 

 under water is practically immune from decay. The protective agency 

 of water is illustrated by the fact that many of the oak piles in 

 a certain town in Wales which were used in the construction of 

 a dock five hundred years ago are still doing service. It seems clear 

 that the degree of resistance of various kinds of woods to decay 

 depends primarily not upon the texture of the woody tissue but upon 

 the presence or absence of substances in it which fail to support or 

 are directly harmful to the life of destructive fungi. Thus pitch and 

 resin in the soft wood of the conifers and tannin in the cells of the 

 oak are unfavourable to the growth of fungi. During life the bark 

 of all trees is highly resistant to colonization by either fungi or 

 bacteria, and until broken affords complete immunity from their 

 attacks on the enclosed wood. After the death of the tree, however, 

 the bark in many species loses the qualities which made it while the 

 vital processes were active immune to the vital activities of fungi 

 and micro-organisms, and decay may proceed in it much more rapidly 

 than in the wood. This is true in the case of the walnut, beech, 

 tulip, and many other trees whei'e the bark completely decays or 

 breaks up into small fragments while the wood is still in a good state 

 of preservation. In the case of the birch, however, the immunity to 

 decay which characterizes the bark of all living trees persists to 

 a remarkable degree after death. So great is this resistance in the 

 canoe-birch, Betula papyracea, that the wood may completely disappear 

 while the bark is still in a perfect state of preservation and retains 

 the original shape of the tree-trunk. 



The photograph (Text-figure) shows a section of the bark of 

 a birch-tree from Manitoba in which the wood had almost completely 

 decayed and disappeared. This bark shell which retained but a trace 

 of decomposed woody dust, however, is wholly untouched by decay, 

 and similar examples may be observed wherever birches flourish. 



