i8o BOTANICAL GAZETTE [September 



the movement of water, Naegeli's micellar hypothesis being 

 generally accepted, and accounting satisfactorily for the great 

 force with which the water had to be, and is, held. As I under- 

 stand the micellar hypothesis, it regards the water as held 

 between the micellae by its surface tension ; at any rate, it would 

 say that imbibition and surface tension have a common mechan- 

 ical explanation. This is not altered in the least by the fact 

 that the presence of the spaces is dependent on that of the 



w 



water. Since the spaces are indefinitely small, the tension is 

 indefinitely great. In the evaporating surface these spaces 

 become still smaller as they lose water, unless it is immediately 

 replaced from behind, and the meniscuses formed in them are 

 of such ultra-microscopical minuteness that it is easy to suppose 

 they can draw water higher than any tree reaches. Assuming 

 always that the walls were the path of the water, the imbibition 

 theory was thus complete, and not in open discord with contem- 

 porary physical science. As this was not true of any other 

 theory it was but natural that this one was generally accepted, 

 and by a sort of reflex action this strengthened the faith in its 

 premise as to the path. 



The identity of imbibition and capillarity was postulated by 

 DeLuc (1791: 12), but on evidence — the imbibition of alcohol 

 and ether — which has not been found generally sound. Hof- 

 mcister (1862:100) and Unger (1868), who were forerunners in 

 the modern development of the theory, treated them as the 

 same, as did Pfeffer in his unqualified acceptance of this theory 

 in the first edition of his Physiology. Naegeli and Schwendener 

 (Mikroskop. second ed. 380) say it is indifferent what the force 

 is called, though formulae based on measurements of tubes 01 

 appreciable size need not apply in these invisible interstices. 

 In 1865 (Handbuch, 213) Sachs entertained no doubt that 

 capillarity and imbibition were related. In 1S79 (Por. d. H.), 

 however, he regarded the phenomena as distinct, and afterward 

 became most insistent on the difference. This robbed the im- 

 bibition theory of its foundation in established physics, and it 

 is very doubtful if it ever could have obtained general credence 



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