IN THE MOTOR ORGANS OF LEAVES. 



121 



wr 



of propagation. Finally, Haberlandt has reverted to the older view with the modi ii cation 

 that, according to him, the stimulant fluctuations in liquid pressure do not normally 

 traverse the wood, but the system of large sieve-tubes in the soft bast which ho regard* 

 as constituting a specific " Reizleitende system.'' 1 His theory agrees with that of the older 

 ters in regarding fluctuations in liquid pressure as serving as mechanical stimuli to 

 the specific contractile apparatus in the motor organs, but affirms that such stimul sit 

 fluctuations are practically solely diffused by means of the sieve-tubes of the soft bast. 

 He does not question the existence of special irritable and contractile ti^ucs in the 

 motor organs, but merely modifies the older view in regard to the precise paths follow* i 

 by the agencies which are assumed to call these into activity. His theory is mainly 

 founded on the fact that he was able to demonstrate that the liquid which exudes from 

 the tissues when they are incised is not mero water, as it should bo if deri\ d solely 

 from the wood, but is in great part composed of materials which are evidently derived 

 from the sieve-tubes of the bast. No one can deny that he has successfully demonstrated 

 this, and has added greatly to our knowledge of the histological details of Mimosa pv lica, 

 but he has certainly not succeeded in proving that his "Reizleitende system" is ^pecin- 

 cally and essentially related to the phenomena of propagation of movement. His own 

 experimental results indeed force him to allow that propagation may occur in spite of 

 the entire absence of his conducting system throughout considerable areas of tissue, but 

 notwithstanding this, his desire to establish the presence of a specific mechanical nervous 



appai 



leads him to adhere to his theory. When he found that propa 



beyond areas which had been entirely denuded of his " Reizleitende system," and is forced 

 to allow that in such cases diffusion of impulses must have taken place through t ho wood, 

 it might have been expected that his views as to the specific value of the system of sieve 

 tubes would have undergone some modification; but apparently they were too firmly 

 subjectively established at the time at which he made the observation to be shaken by 

 any facts which conflicted with them. He had, of course (although he does not appear 



to recognise it) equally clearly demonstrated the fact that propagation could ^ occur 



part from the presence of any continuous system of turgid sieve-tubes, m the 

 experiments on which he founds his decisive rejection of the theory of propaga- 

 tion by means of continuity of living protoplasts. In these experiments he killed 

 the tissues of a certain area in the course of the petioles of leaves by means 

 of boiling them, and then determined the fact that "stimulation" applied at one side 

 of the dead area was followed by the occurrence of movements on the other side. 

 Now this, no doubt, very satisfactorily demonstrated that diffusion of movement could 

 not be essentially dependent on the propagation of impulses along continuous tracts of 

 living protoplasm, but it just as effectually proved that it was not necessarily owing to 

 any propagation of impulses along the course of continuous system of turgid sieve-tubes. 

 The boilino. of the petiolar tissue secured the interposition of an area of dead protoplasm, 

 but it just as certainly secured the interposition of an area devoid of turgidity, and in 

 addition to this of an area within which an abnormal leakage of water was present 

 He was evidently aware of the latter fact, as he specially alludes to the necessity winch 

 arises in such cases of taking special means to prevent the drying up of the parts 

 beyond the boiled area, but, in spite of this, he appears to assume that the tur- 

 gidity of the sieve-tubes remained intact. The position is an incomprehensible one ; he 

 demonstrates that the presence of a continuous system of turgid sieve-tubes, and even 



Ann. Boy. Bot. Gard. CALCTrrA Vol. VI. 



