MOVEMENTS DUE TO SWELLING, ETC. 417 



smoothed out again when water is reabsorbed ; then only does a closing move- 

 ment of the lips of the anther take place. 



It must be admitted that the mechanism of the anther has not as yet been 

 so completely explained on the basis of the cohesion hypothesis as that of the fern 

 sporangium. Indeed, this explanation has been combated by Schwendener 

 <I902). It appears to us, however, that the cohesion hypothesis has more to 

 be said for it than any other of the numerous explanations hitherto given, but 

 into the discussion of which we cannot enter (compare Steinbrinck, Ber. d. 

 bot. Gesell., 1898-1903). It has been shown also, both by Kamerling (1898) 

 and Steinbrinck (1899 b), that cohesion and not imbibition may play an impor- 

 tant part in many other phenomena of movement, such as those seen in the 

 sporangia and elaters of Hepaticae, in water-tissues, and in the pappus of certain 

 Compositae. Into the discussion of all these examples, however, we cannot enter 

 here, but we must point out in conclusion that the cohesion of water of imbibi- 

 tion may possibly co-operate with processes connected with absorption, so that 

 the contrast between these two sets of phenomena may not be so striking as 

 would at first sight appear. Here we come once more to a point which we 

 previously (p. 409) only hinted at. We saw that, according to Butschli, a 

 body capable of swelling has an alveolar structure, that the alveoli were filled 

 with water when the body was in the swollen state, and that the walls of the 

 alveoli collapsed when the body became desiccated. The forces which lead 

 to the deformation of the alveolar walls we have now no difficulty in recognizing 

 as those due to cohesion-tension in the evaporating liquid of the alveoli, and 

 we might compare a single alveolus with the fibrous cell of the anther-waU. 



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