5o8 SECONDARY CHANGES. 



undergoes, according to Nordlinger, no change, at least as regards the outward 

 appearance and coarser physical characteristics of the wood. These are termed 

 alburnum trees by Nordlinger \ In most woods changes of the chemical ^ and 

 physical character, and in a less degree of the structure also, take place sooner 

 or later with the increasing age of the successive zones. These changes represent 

 the beginning of that process of degradation which ends with decomposition, and 

 as they proceed the wood ceases to be available for its original physiological work', 

 with the exception of the purely mechanical function in the case of those woods 

 which become harder. Externally a darker colour appears, which varies in the 

 different kinds of wood, and may become deep black, as in the Ebony woods, dark- 

 green as in Guaiacum wood, or red and violet as in the dye-woods of the Csesalpiniae, 

 Pterocarpus, Haematoxylon, &c. With these changes is very often connected an 

 increase of the specific weight and hardness, and a diminution of the contained 

 water*; in a word the technical value of the wood is created or enhanced by these 

 changes. In this case especially the terms ' ripe-wood ' and ' heart-wood ' are used ; — 

 the two names being applied rather arbitrarily to the particular cases, or used for 

 successive stages. 



The formation of hard and lasting duramen is however only a special case of 

 the incipient process of degradation. The latter may also lead quickly to the 

 opposite result. According to Nordlinger ^ if I understand him rightly, ' many soft 

 woods, e.g. Canadian poplar, and several kinds of Willow,' have a brown heart-wood, 

 which is not distinguished from the alburnum either by higher specific gravity, or by 

 hardness and durability, but, on the other hand, shows a tendency to rapid decom- 

 position, accompanied by the growth of mould. The complete disorganization 

 of the wood, which in many cases takes place in old living trees, is an allied 

 phenomenon which will be discussed below. 



Apart from these changes, anatomical investigation does not demonstrate any 

 alteration in the original structure and the original thickness of wall of the cells and 

 tubes, on the formation of the heart-wood, but merely changes in the material 

 properties of the walls, and in the contents. The membranes are infiltrated by 

 heterogeneous organic bodies, and the latter often appear in the interior of the 

 elements, which they fill up more or less completely, as w^ell as in any cracks and 

 crevices that may be present. The colours of heart-woods are those of the in- 

 filtrated substances. 



Qualitatively, the latter' are usually combustible organic compounds, showing 

 extreme variety in detail, if all the cases be taken into consideration. While referring 

 to the technical literature ", it is here sufficient to call to mind the dyeing substances 

 and chromogenetic bodies of the dye woods, and the infiltrations of resin in the 

 wood of many Coniferae, Guaiacum, &c. As regards these substances, it is by no 



^ Technische Eigensch. d. Hoher, p. 28, &c. 



^ Compare the summary in Hofmeister, Pflanzenzelle, p. 247, and the technical literature. 



^ Rossmassler, Tharander Jahrb. IV. p. 186 (according to Nordlinger). 



* On these subjects, which do not concern us further, compare Nordlinger, /. c, and Wiesner, 

 Rohstoffe, cap. 13. 



5 /. c. p. 36. 



* Compare the summary in Wiesner, /. c. 



