IV.] VARIOUS THEORIES, &c. loi 



vessels, &c. and then to cut away the opposite side of 

 the stem down to the pith, thus making the exposed 

 parts translucent. His results coincide with those of 

 Vesque. 



In the Berichte der deutschen hotaniscken Gesell- 

 schaft for 1883, appeared a criticism by Zimmermann,^ 

 which must not be passed over. He points out that 

 in spite of the favourable features in the more gener- 

 ally approved theories, which explain the water- 

 movements as taking place in the cavities, and not 

 the walls of the elements, they still sin terribly against 

 the laws of physics. It is quite right, he says, to insist, 

 as Boehm and others do, on the importance of the 

 chapelet de Jamifz as a stable column, but the con- 

 ditions in the plant do not allow of capillarity being 

 employed as Boehm and Hartig employ it. 



For if we suppose that the intervening membranes 

 of superposed tracheides composing a column of 

 water and air-bubbles, present no resistance, then the 

 column simply resolves itself into a sinuous contin- 

 uous w^ater column, the axis of which turns aside at 

 the air-bubbles. Such a column is supported by the 

 upper meniscus, and can only be as high as accords 

 with the law of capillarity for the particular tube. 



^ " Zur Kritik der Bohm-Hartigschen Theorie der Wasserbeweerung 

 in der Pflanze." Ber, d. d. hot. ges. B. i. p. 183. 



