1902] RISE OF THE TRANSPIRATION STREAM 269 



When Pfeffer (1892:258-267) attacked the problem of the 

 rise of sap, by the method of eliminating impossibilities, Stras- 

 burger had cut out the assistance of living cells as this last resort ; 

 though Pfeffer was so reluctant to be left without any that he 

 questioned the sufficiency of Strasburger's proof. As far as 

 Pfeffer reached any conclusion, it is this (260) : '* Ohne irgend 

 einc bestimmte Voraussetzung iiber die Mechanik der Wasser- 

 bewegung in den Leitbahnen, kommen wir also zu dem, librigens 

 auch schon aus anderen Argumentationen gezogenen Schlusse, 

 dass das Wasser anderweitig, d, h. durch in den Leitbahnen 

 entwickelte Krafte, in die Hohe geschafft und somit das in sol- 



cher ( ! ! ) VVeise auf hoheres Niveau gehobene Wasser den 

 aus den Gefassbiindeln schopfenden Zellen geboten wird." *' Wie 

 aber im Naheren der Betrieb zu Stande kommt, ist ganzlich 

 unaufgeklart." 



X. Of the various theories on the ascent of the sap we have 

 found no other to have so much in its favor, logically and 

 empirically, as that which says the ultimate cause of the upward 

 movement of water in the wood to replace the loss by transpira- 

 tion is the pressure of the atmosphere against the water absorbed 

 by the roots. To the sufficiency of this theory it is objected 

 that at most the atmospheric pressure can push water up only 

 10"", and this objection is not refuted, but rather better applied, 

 when it is pointed out that the downward pressure of water 

 actually occurring in transpiring trees of whatever height is never 

 such that one atmosphere cannot overcome it. The kernel of 

 the whole problem is, why is this atmospheric pressure exhausted 

 so slowly with the ascent of the tree that, whatever height is 

 reached, and however rapidly and forcibly water may be drawn 

 from the wood, some pressure always remains? 



Vesque (1884:195) proposes that in measuring the 10" 

 which the atmosphere can push up only the indices of water 

 between the bubbles should be counted, for the bubbles have no 

 effective weight. The suggestion is good as to water at rest ; 

 and would be valid and final as to the rising stream if the bub- 

 bles moved with the water ; then our problem would have been 



