1 82 BOTANICAL GAZETTE [September 



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to the abnormal direct atmospheric pressure against cut surfaces; 

 but without reason, as Van Tieghem (1870:278 seq>) found 

 decoctions absorbed by sound seedlings of Leguminosae confined 

 to the lumina of the vessels. Owcc the imbibition theory was 

 undermined, older objections to it, some of which Bohm had 

 been constantly raising, were granted recognition. It was incon- 

 testable that lamina of at least a part of the conducting elements 

 contained water; the imbibition theory could offer no explana- 

 tion at all of its presence (Bohm, 1878:225; Sachs, 1887:247). 

 The absence of a parallel between transpiration and absorption 

 (McNab, 1874:356; Vesque, 1878) was therefore unintelligible 

 to imbibitionists. The excessive difference in the facility of 

 transverse and longitudinal movement of water was not intelli- 

 gible on the basis of the distribution of the water of imbibi- 

 tion, the difference in other physical properties of the wood 

 walls being relatively small. The drying out of dead branches 

 of living trees would seem impossible according to the imbibi- 

 tion theory. And there are other minor objections to it which 

 need not be touched upon here. 



Our permanent debt to the founders and supporters of the 

 imbibition theory is for placing great emphasis on the easy pas 

 age of water through the wood, 3 and for suggesting a physical 

 means for this passage. The water cannot escape passing through 

 occasional walls as it rises. And the work of Errera and or 

 Dixon and Joly, already cited, testifies that some water, though 

 far from enough to satisfy the demands of transpiration, can 

 travel in the walls for a considerable distance. 



VII. An active role in the elevation of the water has been 

 ascribed by many writers to capillarity in the lumina of the ele- 

 ments of the wood.* At the same time it has been recognized 



3 Even this is disputed by Janse. 



-* Recognizing of course that capillarity is not an ultimate source of energy tor 

 the rise, but that this is furnished when the water is evaporated. It would indeed e 

 a careless attempt at an explanation which should seek in capillarity the energy 

 keep a stream moving upward; still, I cannot agree with Kamerling that this wou 

 be a ** logical error," since the law of the conservation of energy does not itself res 



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on logic. 



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