ii6 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



discovered by Von Hohnel ; but which he thinks 

 prove not that air-bubbles under low pressure exist 

 in the transpiring plant, but the existence of a partial 

 vacuum or space filled with aqueous vapour. 



Dufour's experiments are severely criticised. The 

 author agrees with Russow that the lumina of the 

 bent shoots were not completely closed, and asks, 

 with Hartig, how it could have been expected they 

 should be, seeing that so many of the elements have 

 comparatively prominent networks and thickenings 

 projecting into the lumina. As regards the sawn 

 branches, the water passes laterally between the two 

 cuts, traversing the bordered pits. 



Scheit also insists that Dufour failed to press water 

 through his branches, because the air got in, and found 

 that it was by no means difficult to press liquids 

 through if the cuts were made under water. 



He also offered an improvement on Elfving's ex- 

 periments, stating that two objections have been made 

 to them. In the first place Elfving removed his 

 branches from the tree, and ran the risk of air enter- 

 ng, and secondly the danger of greasing the cell-walls 

 by the cacao-butter rendered the method objectionable. 

 To obviate the latter of these disadvantages Scheit 

 used gelatine coloured with eosin, and completely 

 confirmed Elfving's results. 



