SAP-WOOD AND HEART-WOOD 685 



coloured heart-wood takes no part whatever in conduction or storage ; 

 its functions are purely mechanical. All the cell-cavities in this 

 central region are filled with various peculiar organic compounds, 

 which likewise often impregnate the cell-walls. Among these 

 substances special mention may be made of the pigments of dye-woods 

 such as the haematoxylin of Log-wood {Haematoxylon camjieckianum), 

 the brick-red brasilin of Brazil-wood (Caesalpinia Sappan), the 

 dark-red santalin of Sandal-wood (Pterocarpus santalinus), the morin of 

 Madura aurantiaca, etc. ; resinous and gummy bodies are also 

 frequently present, while in a variety of deciduous trees (Ailanthus, 

 Primus, Xanthoxylon, GleditscMa, Sorbus) Sanio found certain (at any 

 rate originally) colourless substances, which are distinguished by their 

 resistance to all ordinary solvents. According to Gaunersdorfer, 

 tannins are often included among the substances with which heart- 

 wood is impregnated. 



In addition to these various organic substances, certain inorganic 

 compounds are also not infrequently deposited in heart-wood. Accord- 

 ing to Criiger, for example, considerable quantities of amorphous 

 silica accumulate in the cavities of the cells and vessels in Hirtella 

 silicca, Petraea volubilis and P. arborca, and, in the vessels alone, in 

 Tectona grandis. Molisch has demonstrated the occurrence of con- 

 siderable deposits of calcium carbonate in the duramen and especially 

 in the old vessels of a number of deciduous trees {Ulmus campesteis, 

 Crftis orientalis, Sorbus torminalis, Fagus sylvatica). The deposit of 

 lime " is usually so heavy that, when the wood is burnt, the ash 

 contains solid casts which reproduce not only the shapes of the vessel- 

 cavities, but also every detail in the sculpturing of their walls." Molisch 

 attributes the accumulation of calcium carbonate to the enfeebled 

 conducting capacity of the heart-wood. 



The changes above described naturally cannot fail to affect the 

 physical properties of the wood. Heart-wood is, in fact, denser, 

 harder and, as a rule, also tougher than the sap-wood of the same 

 tree. These properties, which are, of course, responsible for the technical 

 value of heart-wood, are also mechanically advantageous so far as the 

 plant itself is concerned. From the ecological point of view, therefore, 

 one cannot agree with De Bary that " the formation of hard and 

 durable heart-wood is merely an episode of the early stages of 

 degeneration." We must, on the contrary, regard the production of 

 typical duramen, which is both mechanically superior to alburnum and 

 better protected against decay and disintegration, owing to its being 

 impregnated with the above-mentioned peculiar substances, as a per- 

 fectly normal and advantageous modification of the older wood. The 

 complete loss of function, in respect of nutritive metabolism, is 



