122 THE CAUSES OP FLUCTUATIONS IN TUEGESCENCE 



that the presence of sieve-tubes at all, is unnecessary for the occurrence of propaga- 

 tion of movement, and yet maintains that the presence of such a system is specifically 



related to the phenomenon. 



The results which may be obtained where areas in the course of entire axes in 

 place of petioles are killed by means of the local application of heat are even more 

 convincing. Areas of a quarter of an inch in length in the course of axes may be 

 readily killed by boiling, or more conveniently by thoroughly searing them with heated 

 forceps. It is easy to kill several successive areas at intervals along the course of a single 

 axis, and yet propagation of movement will take place from points on the proximal side 

 of the lowest dead area to points situated ,on the distal side of the highest one. For 

 example, taking a small plant and searing the axis in two points so that one or more 

 leaves are situated below the lowest seared area, one leaf between the two seared areas, 

 and several beyond the distal seared area, it will be found that, when external conditions 

 are such as to favour the occurrence of propagation of movements, the application of 

 heat to the base of the axis is followed by action in all the leaves alike, whether beneath, 

 between, or beyond the seared areas (vide Appendix G). It is easy to determine in 

 such cases, by means of sections carried through the entire thickness of the axis, that 



the tissues have been completely killed throughout (Plate V, Fig 7). This, of course, 



demonstrates that any continuity of living protoplasm is unnecessary, and on Haberlandt's 

 theory forces us to assume that the initial impulses originating in his specific conducting 

 system undergo a primary transfer to the wood, a return to the specific conducting 

 system, a renewed transfer to the wood, and a renewed transfer to the specific conduct- 

 ing system, ere they tell on any leaves situated beyond the distal seared area. Surely 

 the specificity of the " Reizleitende system" is, under such circumstances, hard to recognise. 



But it is not only by such experiments that the groundlessness of Haberlandt's 

 assumption may be demonstrated. The phenomena, which have been already described 

 as following the local application of heat to points in mature, hard axes are equally 

 conclusively opposed to it. In such cases, if the diffusion of movement were essentially 

 dependent on the propagation of fluctuations in pressure along a system of tubes filled 

 with liquid, it ought assuredly to take place in both directions alike. But this it most 

 certainly does not do ; for, whilst granting that external conditions are favourable to the 

 occurrence of movements, centrifugal diffusion normally occurs with the greatest certainty 

 and to an indefinite extent, centripetal diffusion is normally entirely absent, and, in the 

 exceptional cases in which it does occur, is entirely limited to the very immediate neigh- 

 bourhood of the site at which heat is applied. In any continuous system of tubes filled 

 •with liquid, the local application of heat to any particular point in its course must 



tably g 



in pressure which must be propagated in both d 



and, if increase in pressure throughout the system were an essential factor in 



determining the 



of movements, movements would certainly manifest them 



in both directions, alike. But as a matter of fact, the rise in pressure is propagated in 

 both directions, whilst movements occur only in one. 



Haberlandt is unquestionably right in maintaining that much of the liquid which 



des from the 



of Mimos% pudica on incision is derived from the highly turgid 

 tissues of the soft bast, but the latter do not hold any truly specific relation to the 



occurr 



of propagation of movement. They provide an apparatus facilitating th 

 dden escape of liquid from the tissues, and hence an apparatus facilitating sudden 



