INTRODUCTION 



no explanation ; it is currently employed by those who handle 

 woods, who naturally speak of a " porous " and not of a " vas- 

 cular " wood. The "analogy on the one hand is to the blood- 

 vessels of the body, on the other to the " pores " of the skin, 

 between which there is little to choose, while to the lay mind 

 the word " vessel " calls up images of many familiar objects which 

 present no analogy whatever to the pores of the wood. May 

 the critics pardon an excusable bias in favour of simple 

 language. 



The Pores are narrow tubes running vertically up the stem, and 

 having the function of conveying air and fluids for the service 

 of the plant. It is not known how long these minute tubes may 

 be. I have blown bubbles through an apparently solid stick 

 of Norwegian Birch four feet long, and I have pumped air through 

 the whole length of a pole nf feet long, and further I have 

 pumped water in a continuous stream through a piece of Ameri- 

 can Birch ten inches long by one inch diameter, from which it 

 ran as fast as it would have done from an open tube of inch 

 bore. I see no reason why these limits should not be exceeded 

 with proper apparatus, especially if straight, well grown, un- 

 injured poles of Oak are used. 



In all but the very young wood the pores contain either air 

 or the accumulations of by-products of the vital activity of the 

 leaves, chiefly gums and resins, and sometimes a curious tissue 

 like a mass of bubbles, which arises as follows. The walls of the 

 cells and pores, when examined under a high power of magnifica- 

 tion, are seen to be " pitted " all over with spots where the 

 tissue is extremely thin. In fact these " pits " are holes closed 

 by an excessively thin membrane, and are usually opposite to 

 similar perforations in the next adjoining cells or pores. If 

 one of the latter becomes empty, this membrane is forced out 

 into the cavity accompanied by some of the living contents, 

 which subsequently divide and multiply after the manner of 

 the Cambium (already spoken of as lying under the bark). 

 There is, however, this difference, that instead of wood-cells, 

 they give rise to this bubble-like transparent mass of tissue 

 called " Thyloses." This will frequently be met with in pores 

 of large diameter where the wood has not- the property of filling 

 its pores with gum or resin. Another kind of filling occurs 

 in certain tropical woods, especially Teak, and appears to be 

 of a mineral nature. According to Sir F. Abel it is " Apatite " 

 and may be seen as white lines on the surface of Teak planks. 

 It is very hard and rapidly dulls the edge of cutting tools. 

 In a certain species of wood from British Guiana (Suradanni) 

 I have seen accumulations of this substance accompanying 

 decomposition, practically replacing the inner rings of " the 



xxii 



