J 



TO SECONDARY CHANGES. 



here only be briefl}' called to the fact, that the anatomical conditions already 

 adduced point to the occurrence of somewhat complicated processes, and that 

 the expressions just used are not intended to prejudge any developmental theory 

 whatever. • 



As a last stage of the changes described, and one which leads to a result 

 opposite to the formation of heart-wood in the technical sense, a displacement 

 of the normal membranes (extending to their complete disappearance) by masses of 

 resin and balsam is stated to occur locally in the woods which produce these 

 substances; in other woods, which do not form resin, a transformation into dis- 

 organised masses of mucilage and gum takes place. The wood of Pinus Strobus 

 and Abies pectinata, which is infiltrated with balsam, dissolves away, according to 

 Wigand ', into a resinous mass, and as this goes on, the walls of the tracheides and 

 cells diminish in thickness, becoming lost eventually in the structureless mass of 

 resin. The canals, an inch in width, filled with balsam, which, according to 

 Karsten^ traverse the wood of species of Copaifera, and similar phenomena 

 reported in the case of the stem of Drybalanops aromatica^ can also, according 

 to the data before us, scarcely arise otherwise than by partial disorganisation and 

 solution of the Hgneous elements. 



The formation of cherry-gum by disorganisation of the wood of the Amygdalese, 

 as described by Wigand, which no doubt belongs to a great extent to the province 

 of pathology, starts sometimes from vessels, sometimes from groups of wood- 

 parenchyma, or medullary spots. Comp. Wigand, /. c. 



In addition to the organic infiltrated substances, considerable accumulations of 

 Silicic acid occur, as found by Criiger * in the old wood of plants which are charac- 

 terised by extensive silicification of almost all their parts, namely of the Chrysobalaneae, 

 Hirtella silicea, Petraea volubilis, P. arborea, and of Tectona grandis. They occur in 

 the lumina of the cells and the vessels (the latter exclusively in Teak wood) as 

 amorphous masses, filling up the space more or less completely. According to the 

 published statements they are not present in the alburnum. The data before us do 

 not allow of any decided judgment as to further differences between alburnum and 

 duramen, as regards the incombustible constituents which they contain. 



In the contents of the cells of the wood, both in the medullary rays and in 

 the ligneous bundles, and also of the thyloses where they occur, a further essential 

 change takes place on the formation of the heart-wood, in addition to those 

 described. This consists in the permanent disappearance of those constituents 

 which characterise the living cell, especially of the universally distributed starch, 

 and in their replacement by air or infiltrations ^ The disappearance of the starch 

 from the cells coincides fairly exactly, in the cases investigated, with the appearance 

 of the other characters of the heart-wood. 



* Pringsheim's Jahrb. III. p. 165. — On the other hand compare also Dippel, Botan. Zeitg. 1863, 

 p. 256. 



^ Botan. Zcitg. 1857, p. 316. 



^ Compare Fliickiger and Hanbury, Pharmacographia, p. 202. 



* Botan. Zeitg. 1857, p. 297. 



' Sanio, Starkefiihrende Zellen, p. 19 (1858). — Id. Botan. Zeitg. i860, p. 202.— A. Gris, Comptes 

 Rendus, 1866, torn. 70, p. 603. 



