24 Henry H. Dixon. 



that the lumina of the tracheae convey the transpiration stream, in 

 face of the view, generally held at that period, that the walls of the 

 conducting tracts are the most efficient channels for the upward- 

 moving water. 



Seeing the fatal objections to which the gas-pressure theory is 

 open, several authors have striven to obtain assistance for this 

 hypotliesis by assuming the water in plants distributed in the form of 

 J a m i n 's chains. To start into motion a column of water interrupted 

 by air bubbles requires a much greater force than would be required 

 to move a continuous water column of the same length. Zimmer- 

 man^) came to the conclusion , in agreement with N a e g e 1 i , by 

 comparing the behaviour of various liquids, that this resistance is 

 most probably due to the surface viscosity of water. S t r a s b u r g e r -), 

 quoting Plateau, believes that the resistance is due to the imperfect 

 wetting of the tube. Owing to this resistance, however produced, a 

 broken column of water in a narrow vertical tube may stand at any 

 height — the weight of the individual portions of the column being 

 supported by the walls of the tube. But of course the resistance 

 which a Jamin's chain oifers to gravitation will be opposed to any 

 other force exerted upon it. Consequently it is quite illegitimate to 

 suppose that atmospheric pressure could raise a Jamin's chain in 

 the tissues of plants to a greater height than it could lift a continuous 

 column. This becomes evident when we remember that the weight 

 of each partial column exerts a downward force which, by hypo- 

 thesis, is less than the resistance opposed to motion. Hence it will 

 be easier for a pressure to lift the continuous column. 



The inadmissability of the application of the properties of the 

 Jamin's chain is evident for other reasons. It is clear that as soon 

 as the water is free to move round and pass the bubbles of a chain, 

 the walls will be relieved of the weight of the water and the water 

 will exert its full hydrostatic head. That this is the case with water 

 in woody tissues appears immediately from the 'drop experiment' and 

 from the observation that water may be pressed freely past the 

 bubbles. Also, it is evident, the oblique and transverse walls prevent 

 the compound column of water and bubbles moving as a whole. The 

 bubbles must be arrested while the water passes on with little 

 resistance. 



Thus so far from the assumption of the presence of Jamin's 

 chains in the wood of transpiring plants being an assistance to the 



^) A. Z i ra m e r m a u , Zur Kritik der Böhm-Hartig' sehen Theorie der Wasser- 

 bewegung-. Ber. d. Deutsch. Bot. Gesell., 1, 188.3, p. 183. Idem, Ueber die Jamin- 

 sche Kette. Ber. d. Deutsch. Bot. Gesell., 1. 1883, p. 384. 



^) E. Strasburger, Ueber den Bau und Verrichtungen der Leitungsbahnen 

 in den Pflanzen. Jena 1891, p. 816. 



