360 Scientific Proceedings, Royal Dublin Society. 



Measurements of the Cross-section of the Elements of tlie Wood of Conifers. 



To obtain an accurate measure of the cross-section of the cells in the wood 

 the following method (3) was adopted : a camera lucida drawing, or a 

 micro-photograph, was prepared of a transverse section of the wood under 

 investigation. This drawing or photographic print was then carefully cut 

 out, the walls, the lumina of the vessels, of the tracheids and of the cells being 

 kept apart and weighed. From these weights the percentages of the total 

 cross-section occupied by the walls and the lumina of the various elements 

 were deduced. 



To estimate the rate of leakage backwards, which must be overcome by 

 the action of the cells before any of the water elevated is available for the 

 transpiration stream, we proceeded as follows : — Pieces of tiie stems of the 

 trees investigated about 10 cm. x 2 cm. were stripped of their bark, and 

 supported in a vertical position ; the upper end of each was kept flooded 

 with water, and the weight of water transmitted thus under unit head in a 

 given time was determined. The water was supplied drop by drop to the 

 upper surface, so that the head did not vary appreciably. The water 

 collecting on the lower surface was drained away by a piece of bibulous 

 paper, so that the discontinuity of drop-formation did not cause an error in 

 weighing. To prevent water passing down on the outside of the woody 

 cylinders a band of vaseline about 2 cm. wide was smeared round the upper 

 end(l). 



The comparative simplicity of the structure of the wood of the conifers 

 adapts them peculiarly to Janse's sclieme, and tlie application of his theory 

 to them is more I'cadily comprehended than it is to other trees. Indeed, as 

 was the case of Grodlewski's theory (6), it seems doubtful whether the theory 

 under discussion presents any advantages over Westermaier's hypothesis 

 (12 and 13) when it is applied to dicotyledonous trees. 



For this reason the measurements mentioned above were first carried out in 

 Finns silvestris (3). A camera lucida drawing was made of a cross-section of the 

 wood of this conifer,and then the luminaof each of the elements, viz., medullary 

 ray cells and tracheids, were cut out of the drawing with a sharp knife. The 

 network composed of the woody walls remained over. The weights of the 

 tracings gave the following percentage areas for each category : — 



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



„ „ tracheids, . . . 61'2 „ 



Walls of tracheids and cells, . . 31'9 ,, 



