1 84 BOTANICAL GAZETTE [September 



offered by a long series of bubbles to longitudinal pressure has 

 given the Jamin's chain a place in some theories (Westermaier, 

 18S3; also Hartig, 1882; Vesque, 1S84), as an arrangement to 

 hold the water up, forces of a different nature being invoked to 



elevate it. Statements as to this resistance of the *' chain m 

 glass tubes are very discrepant (Janse, Naegeli, Plateau — as 

 cited by Strasburger, 1891 '.815 — Zimmerman, 1883); accord- 

 ing to the experimental results of Schwendener (1886: 569) and 

 Strasburger (1891 :8i9) the resistance to the movement of the 

 chain as a whole is not usually very great in tracheae. 



If the pressure against the upper end of such a column of 

 air and of water were diminished or removed, the result would 

 obviously be* an elongation of the bubbles, lifting the water sup- 

 ported by them. This would operate most at the top, and 

 would cease at a point down the column where the resistance to 

 the bubble's expansion was equal to its excess of tension. In this 

 way Schwendener (1893) thinks it likely that the diminished ten- 

 sion in the vessels might be able to lift some water as much as 

 15°" instead of the 10°^ to which a pressure of one atmosphere 

 could lift an unbroken column. Under certain imaginary condi- 

 tions, which as Schwendener showed do not really occur m 

 plants, a much greater height would be possible ; Schwendener 

 (1892:934) suggests such a case in which the bubbles should 

 be 10°''^ long, in which Steinbrinck (1894 : 127) showed that the 

 top of the column might be lifted 142"^. As to the actual length 

 of the bubbles, Schwendener puts the average in Fagus at 0.33"°*^ 

 that of the supported water being 0.14°'°'. Both Schw^endener and 

 Steinbrinck seem to assume in their calculations that a meniscus 

 will retain its full effectiveness in a vacuum, which, as has just 

 been pointed out, is not at all the case. Moreover, such a mech- 

 anism, in lifting water, would accumulate air at the top, and so 

 destroy itself, and therefore (Askenasy, 1895), even if it could 

 lift water once, it could not raise a constant stream. 



During the last decade surface tension has been playing a 

 very prominent part in still another form in explanations of the 

 ascent of sap. The cohesive power of pure w^ater was demon- 



it? 





