STRUCTURE OF WOOD. 



337 



the wood. To this end we must enter somewhat more in detail into the structure 



and the physical properties of wood. In order to avoid unnecessary complications 



we will confine our consideration in the meantime to the wood of Conifers, 



such as the Pine, Yew, and Fir, because these woods possess no vessels, but 



consist only of trachei'des, and are there- 

 fore relatively simple and homogeneous 



in structure. We must state, in the first 



place, the very important fact (shown by 



Theodore Hartig 20-30 years ago, but 



denied later by all phytotomists) that 



the histological elements of the wood are 



nof in open communication one with 



another, and that the bordered pits of the 



wood-cells (and vessels of foliage-trees) 



are not actually perforated, but closed by 



fine membranes. Thence follows that the 



woody body by no means represents a sys- 

 tem of continuous capillary tubes, but is 



formed of chambers distinctly shut off on all 



sides from one another. The purely micro- 

 scopical and anatomical confirmation of 



this fact would, for our purpose, still leave 



room for much doubt, if the closure of 



the bordered pits in the wood were not 



established with absolute certainty in 



other ways. This is done most simply 



by means of the apparatus here figured. 



A piece of the stem of a Fir, or other 



Conifer, several centimetres long, and some 



2-3 centimetres thick, and still provided 

 with the cortex, is cut smooth at both sec- 

 tions, and the one end fastened by means 

 of caoutchouc to a long glass tube which 

 is connected above with a wide vessel : the 

 tube and vessel are now filled with an 

 emulsion of cinnabar which has previously 

 passed through several layers of filter- 

 paper and therefore contains only cinnabar 

 particles of the most extreme minuteness, 

 which even with the strongest magnifica- 

 tion appear merely as dots, and exhibit the 

 so-called Brownian motion. By means of 



the hydrostatic pressure in the apparatus figured the fluid now filters through the 

 wood : the water running off below appears quite clear and free from cinnabar, for 

 the latter remains in the uppermost portion of the wood, not penetrating deeper 

 than some 1-5 to 2 millimetres. The microscopic examination of this piece after 



J 



Fig. 199. — Apparatus for the filtration of water or emulsion 

 of zinnabar through pine wood. The fresh piece of wood ft is 

 fastened by means of india-rubber tubing d to the wide glass 

 tube ci c is connected with the narrow glass tube b (about 

 60 cm. long) by means of a cork. This tube is fastened above 

 to the vessel a, which contains water or emulsion of cinnabar «. 

 The water filtered through the wood passes through the 

 funnel e, and is collected in the graduated vessel y^ 



