234 DISEASES OF TREES 



butes to the induration of the exposed mixture of resin and 

 turpentine. 



If a conifer be felled or a branch removed, either during 

 summer or winter, one very soon perceives an exudation of resin 

 from the alburnum (" sap-wood ") of the cut surface. But in 

 the case of the pine, spruce, and larch no resin exudes from the 

 older parts of the wood, although these parts are frequently 

 more resinous than the alburnum. I believe that this state of 

 things may be easily explained by the fact that not only are 

 the cell-walls of the alburnum completely saturated with water, 

 but the lumina of the tracheids are more than half full of water. 

 In spite of its volatility the turpentine contained in the resin- 

 ducts is unable to distribute itself throughout the wet wood, 

 and in the case of a wound is forced out of the canals. When 

 the wood, with advancing age, loses its power of conducting 

 water, and so becomes drier no matter whether this is accom- 

 panied by the formation of duramen (" heart-wood ") or not 

 there is nothing to .prevent the turpentine spreading throughout 

 the wood. Not only does it spread into the cell-walls and 

 impregnate them with resin, but it is also deposited in the form 

 of drops on the walls in the lumina of the tracheids, and in 

 fact the lumina are not unfrequently completely filled with tur- 

 pentine or resin. In this way old pine-wood is frequently so 

 saturated with resin that sections as thick as one's finger become 

 partially transparent. Should a section be made of old wood 

 that can no longer conduct water, there will be no exudation 

 of turpentine, for the reason that it has become a part of the 

 walls of the tracheids, or has been deposited in their lumina. 



This also explains why the alburnum becomes completely 

 impregnated with resin when, in consequence of a wound, its 

 outer layers are exposed and dry up. The water that is lost 

 by evaporation is at once replaced by turpentine, which is 

 conveyed in abundance from other parts by means of the resin- 

 canals. The resinous impregnation of these outer layers forms 

 a protection against further injury from the environment. 



The resinous saturation of the old stools of conifers, and the 

 distribution of the turpentine in trees whose wood is being 

 decomposed by parasitic fungi, are very peculiar. The 

 turpentine moves from the decomposed parts to the boundary 



