THE FUNCTIONS OF THE WOOD 



209 



were in some cases very variable, it was deemed advisable 

 to make a number of photographs of each type of wood, 

 and to cut them up as before described. The portions 

 representing the lumina of the water-conducting elements 

 and of the living cells were preserved separately, as were 

 also those occupied by the cell walls. The relative areas 

 of each were then found by weighing the pieces of paper, 

 and expressing the individual values as percentages of the 

 total. In this manner the following tables were obtained, 

 illustrating the composition of the wood of dicotyledonous 

 trees. A preliminary experiment upon the wood of a 

 conifer, Pinus silvestris, gave the figures here recorded:* 



Lumina of medullary ray-cells . . . . 6-9 per cent. 



tracheids 61-2 



Walls of tracheids and cells .. .. 31-9 



TABLE UV. 



Ilex aquifolium : AREAS OF THE ELEMENTS OF THE WOOD IN 

 CROSS -SECTIONS. 



The results obtained with Ilex may be taken as illus- 

 trating the variations met with in the individual deter- 

 minations. In trees, such as Acer, in which the medullary 

 rays are very large, a wider divergence is found between 

 separate measurements. 



In Table LV. are given the mean values for the wood 



* These were obtained by cutting up a camera lucida drawing instead 

 of a photomicrograph. 



14 



