84 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



The solid thick parts are necessary to prevent crush- 

 ing, and the thin places are always easily permeable 

 to water but not to air. As regards the parenchyma 

 cells of the wood, their protoplasmic contents point to 

 their having some other duty to perform, but they may 

 also be employed : so also with the medullary rays. 



On the whole Boehm's idea seems to be most in 

 accord with the facts so far, the easy permeability for 

 water and the resistance to the passage of air being 

 the chief factors. Nevertheless, one seems to see that 

 Elfving was too wide awake to the obvious physical 

 defects of Boehm's theory to give it his support further 

 than the foregoing implies. Here, again, however, I 

 leave further remarks and criticisms to develop 

 naturally in the course of the controversy. 



I may now take together two papers by Robert 

 Hartig 1 which appeared in 1882 and 1883 respectively. 

 The conflicting views then abroad led him to examine 

 the question of the distribution of air and water in 

 wood, and some interesting discoveries were made by 

 the way. In the first place he found that the 

 duramen always contains water, though it is incap- 



1 " Ueber die Vertheilung der organischen Substanz, des "Wassers 

 und Luftraumes in den Baumen, und fiber die Ursache der "Wasser- 

 bewegung in trans pirirenden Pflanzen." Unters. aus d. Forst. Bot. 

 Inst. zu Miinchen ii. and iii. 



