96 TIMBER AND SOME OF ITS DISEASES [CHAP. 



times of the year, which gave him the data for the 

 generalisation as to the distribution and condition of 

 the air as we ascend the tree ; from the tables he 

 constructed curve-diagrams, finally evolving his hypo- 

 thesis as sketched above. 



The next paper of importance is one by Dufour, 1 

 and consists in a deliberate attempt to vindicate 

 Sachs' imbibition theory against the criticisms to 

 which it had been subjected. 



The author maintains that although various move- 

 ments of water occur from lumen to lumen of the ele- 

 ments of the wood, and by filtration through the pits, 

 these have nothing to do with the transpiration cur- 

 rent : it is as water of imbibition in the walls that the 

 rapid flow concerned in transpiration occurs. He 

 considers that Elfving's experiments in no way over- 

 throw the theory, because they only prove filtration 

 under pressure, which is not denied : pressures of this 

 kind, however, cannot affect the equable distribution 

 of imbibed molecules in the cell-walls. Sachs had 

 already insisted that the water is in a peculiar condi- 

 tion infinitely mobile, but removed from the influence 

 of gravitation or of ordinary pressures. 



In regard to R. Hartig's criticisms, (i) that the 



1 " Ueber den Transpirationstrom in Holzpflanzen. " Art. dcs hot. 

 Inst. in Wiirzburg, 1883. 



