464 
He assumes that the air, arriving to the top of the tracheal 
system, will ,,escape" through the stomata. — It is unknown in 
physics that rarefied air ,,escapes" to the atmosphere. 
He assumes that the bordered pits between two tracheids, one 
above the other, in the wood of the Coniferae act like artificial 
valves opening upwards, only very much better; while the pits be- 
tween tracheids on the same level are assumed to act in quite 2 
different way. — As there is no difference in the strueture of all 
these pits, there can evidently be no difference in their mode of 
action, and since the two sides of a bordered pit are identical, it 
must be impossible that the pits should act like valves opening 
towards one side only. [ 
VI. " The origin and fate of the gas i the tracheae is a very 
dark point in our knowledge concerning the ascent of sap. It ought 
to be investigated and can be investigated through rather simple 
methods, briefly set forth in the Danish paper. 
30. December 1902. 
